CA1114984A - Manufacture of styrene polymers which have been modified to improve their impact strength - Google Patents
Manufacture of styrene polymers which have been modified to improve their impact strengthInfo
- Publication number
- CA1114984A CA1114984A CA273,939A CA273939A CA1114984A CA 1114984 A CA1114984 A CA 1114984A CA 273939 A CA273939 A CA 273939A CA 1114984 A CA1114984 A CA 1114984A
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- Canada
- Prior art keywords
- styrene
- rubber
- polymerization
- weight
- shearing
- Prior art date
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F279/00—Macromolecular compounds obtained by polymerising monomers on to polymers of monomers having two or more carbon-to-carbon double bonds as defined in group C08F36/00
- C08F279/02—Macromolecular compounds obtained by polymerising monomers on to polymers of monomers having two or more carbon-to-carbon double bonds as defined in group C08F36/00 on to polymers of conjugated dienes
Abstract
ABSTRACT OF THE DISCLOSURE
The invention is concerned with a process for the manufacture of a styrene polymer modified with rubber to improve its impact strength, by polymerizing styrene in the presence of 1 to 20% by weight, based on styrene, of rubber in at least two stages, wherein, in a first stage, the styrene, which contains the rubber in solution, is prepolymerized at from 50 to 150°C
in the presence or absence of inert diluents, while breaking up the disperse soft-component phase which forms during the polymerization by shearing the polymerization mixture until the quantity of styrene converted, based on the starting solution to be polymerized, corresponds to from 3 to 10 times the amount of elastomer constituent of the total amount of rubber employed and the particles of the disperse soft component phase thus formed have a mean diameter of less than 6 µm, and thereafter, in one or more further stages, the polymerization is completed by taking it to the desired conversion with reduced shearing or entirely without shearing, in mass, in solution or in aqueous suspension. The process of the invention is characterized in that the shearing during prepolymerization is carried out in such a way that the particles have a weight-average mean diameter of less than 1 µm and a narrow particle-size distribution, and the disperse soft-component phase contains, during the prepolymeriza-tion, from 35 to 65% by weight of free or chemically bonded polystyrene segments being incorporated into the rubber component in a chemically bonded form as a polymer block or a grafted branch, the segments having a number-average molecular weight of at least 30,000. The styrene polymers obtained exhibit not only high impact strength but also improved transparency, and may be used for packaging purposes.
The invention is concerned with a process for the manufacture of a styrene polymer modified with rubber to improve its impact strength, by polymerizing styrene in the presence of 1 to 20% by weight, based on styrene, of rubber in at least two stages, wherein, in a first stage, the styrene, which contains the rubber in solution, is prepolymerized at from 50 to 150°C
in the presence or absence of inert diluents, while breaking up the disperse soft-component phase which forms during the polymerization by shearing the polymerization mixture until the quantity of styrene converted, based on the starting solution to be polymerized, corresponds to from 3 to 10 times the amount of elastomer constituent of the total amount of rubber employed and the particles of the disperse soft component phase thus formed have a mean diameter of less than 6 µm, and thereafter, in one or more further stages, the polymerization is completed by taking it to the desired conversion with reduced shearing or entirely without shearing, in mass, in solution or in aqueous suspension. The process of the invention is characterized in that the shearing during prepolymerization is carried out in such a way that the particles have a weight-average mean diameter of less than 1 µm and a narrow particle-size distribution, and the disperse soft-component phase contains, during the prepolymeriza-tion, from 35 to 65% by weight of free or chemically bonded polystyrene segments being incorporated into the rubber component in a chemically bonded form as a polymer block or a grafted branch, the segments having a number-average molecular weight of at least 30,000. The styrene polymers obtained exhibit not only high impact strength but also improved transparency, and may be used for packaging purposes.
Description
i4C~
O.Z. 31,926 MANUFACTURE OF STYRENE POLYMERS WHICH HAVE BEEN MODIFIED TO IMPROVE
THEIR IMPACT STRENGTH
The present lnvention relates to a process for the manufacture Or styrene polymers which have been modified with rubber to improve their impact strength, and which are fairly transparent in thin layers.
It has been disclosed that the impact strength of polystyrene can be improved by incorporating a rubbery material into it. To achieve this, the two components can be mixed mechanically or, advantageously, the polymerization of the styrene is carried out ln the presence of the rubber.
In the case of the last-mentioned method, the procedure is, ln general, to dissolve the rubber in the monomeric styrene and then to polymerize this starting solution, continuously or batch-wise, in mass, in solution or in a combined mass/suspension poly-merization process. Immediately after the start of the polymeriza-tion reaction, the solution, to be subjected to polymerization, of the rubber in the monomeric styrene separates into two phases of whlch one, namely a solution of the rubber in monomeric styrene, lnitlally forms the oontinuous phase whllst the other, namely e .~
.
., ' . ~
lg~4~
0. z . 31,926 solutlon of the resulting polystyrene in its own monomer, remains suspended as droplets in the said phase. With increasing conversion, the amount Or the second phase increases at the expense Or the first, as the monomer is consumed; as soon as the amount of polystyrene formed exceeds the amount of rubber employed, a change in phase continuity takes place. When this phaseinversion o~curs, drops of rubber solution are formed in the polystyrene solution; however, these drops of rubber solution, for their part, firmly enclose smaller droplets of what has now become the continuous polystyrene phase. At the same time, a grafting of the rubber by polystyrene chains takes place during this polymerization. As a rule, the poly-merization is carried out in several stages. In the first polymeri-zation stage, i.e. the prepolymerization, the solution of rubber in styrene is polymerized, whllst exposed to shear, until a conver-sion beyond the phase inversion point is reached, and thereafter polymerization is continued, to the desired conversion of styrene, under reduced shear or entirely without shear. Continuous mass poly-merlzation or solution polymerization is described, for example, in U.S. Patents 2,694,692, 3,243,481 and 3,658,946. Batchwise combined mass/suspension polymerization is disclosed, for example, in U.S. Patent 3,428,712.
In all these polymerization processes, shearing the reaction mixture in the first process stage, ie. during the prepolymerizationJ
ls of particular importance~ As is known, for example, from U.S. Patent 3,243,481 and British Patent 1,005,681, the particle size of the disperse soft-component phase is brought to a suitable value, during this prepolymerization, by means of the field of shear forces generated by suitable stirring devices; this particle size is a factor of the greatest importance to the mechanical pro-perties of the resulting polystyrene of improved impact strength.
Since the distribution of the disperse soft-component phase can only take place after the phase inversion, the shearing of the poly-merization mixture immediately after phase inversion is a deciding ~ ~c3~ ~ O.Z. 31,926 factor in ad~u~ting the particle size of the disperse soft-component phase. For this reason, the prepolymerization is as a rule taken to a styrene conversion equivalent to from 1.2 to 2 times the amount o~ rubber employed. Shearing far beyond the phase inverslon, ie. up to a conversion corresponding to more than twice the amount of rubber employed, has no significant influence on the particle size of the disperse soft-component phase and is therefore generally not customaryO In addition, the properties of the styrene polymers of improved impact strength can be influenced and varied during the polymerization, for example by using molecular weight regulators or special catalystsO
The styrene polymers, modified to improve their impact strength, which have been manufactured by these conventional processes thus consist of two phases, namely a homogeneous continuous phase (matrix) of the styrene polymer, in which rubbery particles of the soft component are embedded as the disperse phase. The soft com-ponent consists of styrene-grafted rubber particles which contain a greater or lesser amount of occluded matrix material. In the case o~ styrene polymers of high impact strength which have been optimized in respect of mechanical properties, the scatter in particle size of the disperse soft-component phase, expressed in terms of the diameter, in accordance ~lth Appl.Polymer Symposia 15 (1970) page 74 (d), is from 1 to 5/um, and the mean value, ie. the optimum diameter, is thus 3/um.
Because of the incompatibility of the rubber phase with the matrix material and because of the size of the rubber particles ln the disperse soft-component phase, the styrene polymers of high impact strength, and utensils manufactured therefrom, are cloudy and opaque, so that they are unsuitable, or only partially suitable, ~or use in certain fields where a certain degree of transparency is desired, for example the packaglng field. It is, therefore, of interest to provide styrene polymers of high impact strength which, in addition to the conventional good mechanical properties, exhibit .4~ 0.z. ~1,926 a certaln transparency, ie. are at least translucent.
It has been disclosed that the transparency of thermoplastlc polymers which have been modified to improve their impact strength can be improved by matching the refractive lndlces of the hard component and soft component, for example by copolymerizatlon wlth sultable monomers, eg. methyl methacrylate. However, thls measure fundamentally alters the pattern of properties of such molding compositions, eg. the solvent resistance, the melt flow, the soften-ing range or the mechanical properties. This method of lmprovlng the transparency is therefore unsultable ln cases where the fleld of use demands a certain pattern of properties of the styrene poly-mers whlch have been modlfled to lmprove their lmpact strength, for example the comblnation of rigldity and toughness requlred for use ln the packaglng field.
It has also been dlsclosed that the transparency of two-phase systems can be lmproved by lowerlng the partlcle slze of the dls-perse phase to below the wavelength of vlsible llght. However, by merely reduclng the diameter of the rubber partlcles of the dlsperse soft component phase by appropriate technologlcal methods ln the conventlonal processes for the manufacture of polystyrene of high lmpact strength lt ls again not possible to lmprove the transparency wlthout greatly detracting from the mechanlcal propertles.
It ls an object of the present invention to provide a process which permits the manufacture of styrene polymers which have been modified wlth rubber to improve thelr impact strength, and whlch exhlblt not only good mechanical properties but also lmproved transparency. The mechanlcal propertles of the products should sub-stantlally correspond to the styrene polymers of high lmpact strength manufactured by conventlonal processes, and the products should be at least translucent ln thln layers.
We have found, suprlsingly, that this object ls achleved and that such products are obtained if, during the polymerizatlon of styrene ln the presence of the rubber, the shearlng during the prepolymerizatioll is carried ollL in a specific manner and the disperse soft-component phase llas a particular defined composition after phasc inversion at a particular conversion.
Accordingly, the present invention relates to a process for the manufacture of a styrene polymer modified with ~rubber to improve its impact strength, by polymerizing styrene in the presence of 1 to 20~ by weight, based on styrene, of rubber in at least two stages, wherein, in a first stage, the styrene, which contains the rubber in solution, is prepolymerized at from 50 to 150C in the presence or absence of inert diluents, while breaking up the disperse soft-component phase which forms during the polymerization by shearing the polymerization mixture until the quantity of styrene converted, based on the starting solution to be polymerized, corresponds to from 3 to 10 times the amount of elastomer constituent of the total amount of rubber employed and the particles of the disperse soft component phase thus formed have a mean diameter of less than 6 ,um, and thereafter, in one or more further stages, the polymerization is completed by tak~ng it to the desired conversion with reduced shearing or entirely with~out shearing, in mass, in solution or in aqueous suspension. The process of the invention is characterized in that the shearing during prepolymerization is carried out in : such a way that the particles have a weight-average mean diameter of less than 1 ym and a narrow particle-size distribution, and the disperse soft-component phase contains, during the prepolymer-ization, from 35 to 65~ by weight of free or chemically bonded polystyrene segments being incorporated into the rubber component in a chemically bonded form as a polymer block or a grafted branch, the segments having a number-average molecular weight of at least 30,000.
Rubbers which can be employed in the process according to the invention are the natural or synthetic rubbers conventionally used for modifying styrene polymers to improve '~.
1~~
their impact strenc3th. Suitable rubbers are not only natural rubber but also, for example, polybutadiene, polyisoprene and copolymers of butadiene and isoprene with one another or with styrene and/or other comonomers, these copolymers preferably having a glass transition temperature below -20C. The rubbery copolymers of butadiene and/or isoprene may contain the monomers either in random distribution or as blocks. Further suitable rubber components for the process according to the invention for the manufacture of styrene polymers which have been modified to improve their impact strength are rubbery ethylene-propylene copolymers and ethylene-propylene-diene terpolymers.
The elastomer constituent of a rubber is to be understood as the total amount of the rubber minus any chemically bonded constituent comprising a glassy thermoplastic, eg. poly-styrene, in, for example, the form of blocks or grafted branches.
The elastomer content of a styrene-butadiene block copolymer containing 30% of polystyrene blocks is accordingly 70~. This - applies even if, over and above the 30~ of polystyrene blocks, the polybutadiene constituent contains further styrene units in random distribution.
The preferred rubber to use is a homopolymer of a conjugated diene of 4 to 6 carbon atoms, especially polybutadiene.
Elastomeric styrene-diene block copolymers or styrene-diene graft copolymers are equally suitable. The graft copolymers contain polystyrene side branches grafted onto a polydiene, preferably polybutadiene, as the substrate. In the block copolymers, the transition between the individual blocks may be sharp or blurred;
in particular, block copolymers of the general formula A-B or A-B-A may be used. In these formulae, A is a homopolystyrene block and B a homopolymer C~
0,Z. 31,926 block of a con~ugated dlene of 4 to 6 carbon atoms, especlally butadiene, or a copolymer block of a con~ugated dlene, especially butadlene~ with styrene, with random distributlon of the monomers.
The rubbers may be used indlvidually or as mixtures wlth one an-other. The total amount of rubber employed should, however, at most contain 55 per cent by weight of homopolystyrene segments in the form of blocks.
To carry out the process according to the invention, the rubber is first dissolved in the monomeric styrene, and this start-ing solution is then polymerized. In general, the rubber component ls employed in amounts of from 1 to 20 per cent by weight, prefer-ably in amounts of from 2 to 15 per cent by weight, based on the starting solutlon to be polymerized.
The starting solution is polymerized in at least two stages;
in the first stage the monomeric styrene, which contains the rubber in solution, ls prepolymerized in mass or in solution, under the action of shearing forces, and thereafter the polymerization is completed in one or more subsequent stages, under reduced shear or entirely without shear, in mass, solution or aqueous suspension.
The prepolymerization in the first process stage is carried out at from 50 to 150C. The polymerization can be started thermally or by means of initiators which form free radicals. In the case of mass polymerization, the monomeric styrene, containing the rubber in solution, is polymerized directly; in the case of solution poly-merization, up to at most 50 per cent by weight, preferably up to ~0 per cent by weight, based on monomeric styrene employed, of an inert diluent are also added to this starting solution. Usually, at least 2 per cent by weight, preferably from 5 to 10 per cent by weight, of the inert diluent, based on the monomeric styrene :~i employed, are used. Examples of suitable inert diluents are aroma-- tic hydrocarbons or mixtures of aromatic hydrocarbons which are liquid at the polymerization temperature. TolueneJ ethylbenzene, the xylenes or mixtures of these compounds are preferred. If appro-O.Z. 31,926 priate, auxlllarles and addltlves, eg. molecular welght regulators, lubrlcants and the like, may be added to the polymerlzatlon batch.
The reactlon mlxture obtalned from the prepolymerlzatlon in the ~irst stage is then ~lnally polymerized to the desired conversion, elther ln mass or in solution, in one or more further stages, suit-ably at up to 200C, or is suspended ln water in the presence of the known conventional water-soluble suspending agents, eg. methyl-cellulose, hydroxypropylcellulose, polyvlnyl alcohol, partially saponified polyvinyl acetates, polyvlnylpyrrolidone and the like, or inorganic dispersing agents, eg. barium sulfate, the suspending or dispersing agents ln general belng employed in amounts of from 0.1 to 5 per cent by weight, based on the organic phase, and is then flnally polymerlzed, as a rule at from 40 to 160C. If the second process stage is carried out ln aqueous suspension, the addition of inert diluents in the flrst process stage is generally dispensed with. In thls combined mass/suspension process the polymerization is usually initlated by adding oil-soluble initiators which decompose to give free radicals, eg. benzoyl peroxide, dicumyl peroxide, di-tert.-butyl peroxide, azodiisobutyronitrile and the like or combi-nations thereof; the prepolymerization can also be started thermally, and in this latter case it ls possible only to add the oil-soluble inltiators ln the second process stage, when carrying out the poly-merlzatlon ln aqueous suspenslon. After completlon of the polymerl-zation, the end productsobtained are worked up in the conventional known manner.
An essential feature of the process according to the invention is how the process is carried out in the first stage, during the prepolymerlzation, which according to the invention should be taken to the point where the amount of styrene converted corresponds to from 3 to 10 tlmes the elastomer constituent of the total amount of rubber employed, these amounts being in each case based on the start-ing solutlon to be polymerized. In order to achieve products having the deslred pattern of properties it is necessary, on the one hand, O.Z. ~1,926 ellberately to adjust the particle slze of the disperse soft-component phase being formed, by the action of an appropriate field of shearing forces, whilst on the other hand the reaction conditions must be balanced so that at the same time the disperse soft-component phase has a specific composition in this range of conversion. Soft component, for the purposes of the present invention, means the constituent which is toluene-insoluble at room temperature (25C), of the polymer which has been modified to improve its impact strength, minus any pigments which may be present. Accord-ingly, the soft component corresponds to the gel content of the pro-duct and consists, as has been explained at the outset, both of the grafted rubber component and of the part of the matrix material (polystyrene) which has been mechanically included in the grafted rubber particles.
The action of shearing forces on the reaction mixture in the first process stage, in order to break up the disperse soft-component phase after phase inversion, is maintained, according to the invention, until the amount of styrene converted corresponds to from ~ to 10 times the elastomer constituent of the total amount of rubber employed, the amounts in each case being based on the starting solution to be polymerized. The shearing of the polymeriza-tion mixture can be achieved in the conventional manner, by appro-priate stirring devices. The particle size of the disperse soft-component phase depends on the rate of stirring, ie. on the shear-ing stress; the higher the latter, the lower the particle size. The relation between rate of stirring and size and distribution of the disperse soft-component particles formed is in itself known and is described, for example, in U.S. Patent ~,24~,481 or by Freeguard, British Polymer Journal 6 (1974), 205 to 228. According to the inven-tion, the shearing should be carried out so that subsequently the particles of the disperse soft-component phase have a welght-average mean diameter of less than l/um together with a narrow particle size distribution. In general, the weight-average mean particle _g_ 4 ~
O.Z. ~1,926 diameter of the particles of the soft-component phase should be from 0.05 to l/um, preferably from 0.2 to 0.6/um. With larger particle diameters, the translucency of the products progressively decreases. The mean particle diameter of the rubber particles of the disperse soft-component phase can be determined, for example, by counting and evaluating electromicrographs of thin layers (cf.
F. Lenz, Zeitschrift fur Wiss. Mikroskopie 6~ (1956), 50-56). The rate of stirring required to achieve the desired particle size depends, inter alia, on the details of the particular apparatus and is known to those skilled in the art or can be established by a few simple experiments.
A further essential feature of the process according to the invention is that, in addition to maintaining the shearing condi-tions in the first process stage, the first process stage must be controlled so that the disperse soft-component phase contains -when the amount of styrene converted is from ~ to 10 times the elastomer constituent of the total amount of rubber employed, the amount being in each case based on the starting solution to be poly-merized - a total of from ~5 to 65 per cent by weight of polystyrene in the form of chemically bonded blocks or grafted branches or at times also as free homopolymer in an emulsified form.
At least 50 per cent by weight of this polystyrene component which ls requlred to be present in the total disperse soft-component phase at the stated conversion must, however, be contalned as chemically bonded polystyrene segments ln the rubber component and must have a number-average molecular welght cf at least 30,000, preferably at least 50,000. The number-average molecular weight of the polystyrene segments of the soft component which are present chemically bonded as a polymer block or grafted branch in the rubber is in general less than 250,000, preferably less than 150,000. The total homopolystyrene content of the disperse soft component can be determined on a sample, taken from the reaction mixture at the appropriate conversion, by means of the conventional analytical ~ O.Z. 31,926 methods, for example by IR spectroscopy. The chemically bonded content of polystyrene segments in the soft component is determined on rubbers containing polybutadiene by flrst extracting free homo-polystyrene with a mixture of methyl ethyl ketone and acetone and then degrading the polybutadiene part of the residual material by means of OSO4 (see, eg. G. Locatelli and G. Riess, Die Angew.
Makrom. Chem. 26 (1972), pages 117-127).
The polystyrene content in the disperse soft-component phase, at a styrene conversion within the stated range, may be adjusted in various ways, and may, for example, be controlled by the polymeriza-tlon temperature, the amount and nature of the initiators, the presence or absence of molecular weight regulators and the like. It depends, in particular, on the nature of the rubber component emp~yRd.
If, for example, the process according to the invention employs a rubber which does not contain any homopolystyrene segments in the form of blocks, such as, for example, a homopolymer of a conjugated diene, especially polybutadiene, it is necessary, in order to achieve the desired composition of the soft component, to carry out the prepolymerization in the first process stage under conditions which favor the grafting of the styrene onto the rubber. In that case, the prepolymerization is not carried out under the conven-tional conditions, thermally or in the presence of initiators at low temperatures; instead, the polymerization in the first process stage is carried out at relatively high temperatures in the presence of initiators which form free radicals, especially initiators which are known to favor grafting. The choice of the polymerization tem-perature depends above all on the inltiator employed; in general,the temperature ls above 100C. In such a case, the prepolymerization is generally carried out at temperatures such that the half-life of the free radical initiator employed, at the polymerization tempera-ture and in the polymerization solution, is less than 30 minutes, preferably less than 5 minutes. The concentratlon of the initiator is from 0.001 to 1.0 mole per cent, preferably from 0.005 to 0.5 ~ O.Z. 31,926 mole per cent, based on the amount of monomerlc styrene employed.
The conventional lnltiators, eg. alkyl peroxides, acyl peroxides, hydroperoxides, peresters, peroxycarbonates, azo compounds and the like, can be employed; lnitiators which favor grafting, eg.
benzoyl peroxide, are preferred. The decomposition of the initia-tors can also be accelerated by suitable additives or appropriate measures.
The procedure ~ust described is applicable not only when using rubbers consisting of homopolymers of con~ugated dienes, but is in principle applicable in the same manner to all rubbers which do not contain styrene and to rubbery copolymers of a con~ugated diene, especially butadiene, with styrene, in which the monomer units are distributed at random. In this process it is also possible to employ block copolymers or graft copolymers of a conjugated diene, especially butadieneJ with styrene, provided the block polystyrene content of the copolymer, ie. the proportion of polystyrene segments present as polymer blocks or grafted branches ln the copolymer, is less than 25 per cent by weight, based on the block or graft copoly-mer; lf this is not the case, there is the risk that the polystyrene content of the disperse soft-component phase may, during the prepoly-merization, be above the limiting value admissible according to the lnvention, in which case products having the desired pattern of pro-perties would no longer be obtained~
When using a block copolymer or graft copolymer of butadiene and styrene which has a block polystyrene content of from lO to 40 per cent by weight, and in which the number-average molecular weight of these block polystyrene segments is more than ~0,000, preferably more than 50,000, as the rubber, the content of polystyrene segments in the disperse soft-component phase within the stated range of conversion of the monomeric styrene can also be brought to the value of from ~5 to 65 per cent by weight, required according to the inven-tion, by adding to the starting solution, to be polymerized, of this blook copolymer or graft copolymer in monomeric styrene, a homopoly-O.Z. ~1,926 styrene whlch has a molecular weight equal to or lower than themolecular weight of the block polystyrene segments ln the block copolymer or graft copolymer. The prepolymerization of the starting solution can then be carried out, in respect of temperature control and catalyst addition, under the conventional conditions normally employed for the manufacture of styrene polymers which have been modified to improve their impact strength. During the polymerization, the homopolystyrene added to the starting solution is incorporated lnto the polystyrene domains of the butadlene/styrene block copoly-mers or graft copolymers and is thus ultimately contained in the disperse soft-component phase, thereby increasing its content of bonded or emulsified polystyrene. The amount of homopolystyrene which is additionally introduced into the starting solution, to be polymerized, of the block copolymer or graft copolymer in monomeric styrene depends on the block polystyrene content of the block co-polymer or graft copolymer used. It must be so chosen that the sum of the block polystyrene content of the block copolymer or graft copolymer and the additionally introduced homopolystyrene is at least 20 per cent by weight, preferably at least 25 per cent by weight, and at most 55 per cent by weight, preferably at most 50 per cent by weight, in each case based on the sum of block copolymer or graft copolymer and additionally lntroduced homopolystyrene.
Further, it is possible to obtain the required content of poly-styrene segments in the disperse soft-component phase by employing, as the rubber, a block copolymer or graft copolymer of a con~ugated dlene, especially butadlene, and styrene, which contalns from 25 to 55 per cent by weight, based on the block copolymer or graft copoly-mer, of polystyrene blocks and in which the number-average molecular weight of the block polystyrene segments is at least 30,000, prefer-ably at least 50,000. The number-average molecular weight of the block polystyrene segments is in general less than 250,000, prefer-ably less than 150,000. If block copolymers with a blurred transi-tion between the polydlene blocks and the polystyrene blocks are -1,~-~ O.Z. ~1,926 used, the transitlon range must be lncluded, for calculatlon purposes, wlth the polydiene block, le. with the elastomer constltuent of the rubber, so that only the pure homopolystyrene segments are treated as the polystyrene block constltuent. The prepolymerization ln the first process stage can ln this case be carried out under the con-ventlonal conditlons in respect of temperature regime and of cata-lyst employed, since, under these condltions, sufflcient polystyrene ls grafted onto the rubber component and is occluded by the rubber particles durlng phase inverslon to give a total content of poly-styrene segments, contained in the disperse soft-component phase in the critical range of conversion of the monomeric styrene, of from 35 to 65 per cent by weight, based on the total disperse soft-component phase at this conversion. If block copolymers or graft copolymers of conjugated dienes and styrene having a high block polystyrene content) of more than 55 per cent by weight, based on the block copolymer or graft copolymer, are employed, the proportion of polystyrene segments ln the disperse soft-component phase at the converslon in question ls always above the range requlred according to the in~ention, and accordingly products havlng lmproved trans-parency are not obtalned.
Such elastomerlc block copolymers or graft copolymers of con-~ugated dienes and styrene, having~ high content of block polystyrene, above from about 50 to 55 per cent by weight, can however be used as the rubber in the process accordlng to the lnventlon if they are employed as a mixture with a homopolymer of the corr~sponding con-jugated dlene. Thls mixture of block copolymer or graft copolymer and homopolymer of the conjugated diene then forms the total rubber component. The proportlon of homopolymer of the conjugated diene in this mixture depends on the block polystyrene conten~ of the block copolymer or graft copolymer and is so chosen that the proportion of block polystyrene in the rubber mixture employed is at least 20 per cent by weight, preferably at least 25 per cent by weight and at most 55 per cent by weight, preferably at most 50 per cent by O.Z. ~1,926 welght, based on the rubber mlxture. The proportlon of the homopoly-mer of the conJugated dlene ln the total rubber mlxture should, however, ln general not exceed 50 per cent by welghtJ based on the rubber mixture. We have found that such a rubber mlxture behaves ln the process as lf it were a block copolymer or graft copolymer havlng a correspondlng content of block polystyrene and accordlngly can be used under the same condltions as the latter ln the process accordlng to the lnvention.
It ls also possible to add a molecular welght regulator durlng the prepolymerlzation (started thermally or by means of lnltlators whlch form free radlcals) of the starting solution, in order thereby to control the proportion of polystyrene grafted onto the rubber, and the molecular welght Or the polystyrene, ln accordance wlth the lnventlon. The molecular welght regulator, the transfer constant of whlch should be at least 1, preferably from 2 to 15, under the reac-tlon conditions is added, preferably ln amounts of at least 0.1 per cent by weight, based on the monomeric styrene employed, to the . .
starting solution at the beginnlng of> or durlng, the prepolymerlza-~; i tlon, prior to the phase lnverslonO
In general, lt can be stated that the prepolymerlzation ln the first stage of the process can be carrled out ln prlnclple ln any deslred manner, provided the two conditlons according to the inven-tion, namely those relating to the shearing of the polymerlzation mlxture and to the composition of the disperse soft-component phase, are fulfllled. The manner ln whlch the polymerlzation is completed ln the second process stage and possibly further process stages ls not essentlal to the lnventlon. As has already been descrlbed, thls flnal polymerization ls carried out in mass, in solution or in aqueous suspension and employs the conventional procedures, such as are described, for example, in the publication cited lnitlally, whlch are hereln lncorporated by reference.
The styrene polymers modlfled to lmprove thelr lmpact strength, which are manufactured ln accordance with the lnventlon have improved :
~ ~ ~4~ O.Z. 31,926 transparency compared to conventional polystyreneswhich have been modified to improve their impact strength, ie. they are translucent and even transparent in thin layers, without this improvement being accompanied by a deterioration of the level of mechanical proper-ties of the materials compared to comparable conventlonal products which are not translucent. In addition, finished articles made from the products manufactured according to the invention exhibit a high gloss. The styrene polymers,which have been modified to improve their impact strength, obtained in accordance with the present in-vention are therefore particularly suitable for use in the packaging field. When used for this purpose, they may contain the conventional additives and auxiliaries.
The Examples which follow illustrate the invention. Parts and percentages are by weight, unless stated otherwise. The products are tested in accordance with the following methods:
1. Yield stress (N/mm2) and tensile strength (N/mm2) were deter-mined on a molded dumbbell-shaped bar according to DIN 5~,455.
O.Z. 31,926 MANUFACTURE OF STYRENE POLYMERS WHICH HAVE BEEN MODIFIED TO IMPROVE
THEIR IMPACT STRENGTH
The present lnvention relates to a process for the manufacture Or styrene polymers which have been modified with rubber to improve their impact strength, and which are fairly transparent in thin layers.
It has been disclosed that the impact strength of polystyrene can be improved by incorporating a rubbery material into it. To achieve this, the two components can be mixed mechanically or, advantageously, the polymerization of the styrene is carried out ln the presence of the rubber.
In the case of the last-mentioned method, the procedure is, ln general, to dissolve the rubber in the monomeric styrene and then to polymerize this starting solution, continuously or batch-wise, in mass, in solution or in a combined mass/suspension poly-merization process. Immediately after the start of the polymeriza-tion reaction, the solution, to be subjected to polymerization, of the rubber in the monomeric styrene separates into two phases of whlch one, namely a solution of the rubber in monomeric styrene, lnitlally forms the oontinuous phase whllst the other, namely e .~
.
., ' . ~
lg~4~
0. z . 31,926 solutlon of the resulting polystyrene in its own monomer, remains suspended as droplets in the said phase. With increasing conversion, the amount Or the second phase increases at the expense Or the first, as the monomer is consumed; as soon as the amount of polystyrene formed exceeds the amount of rubber employed, a change in phase continuity takes place. When this phaseinversion o~curs, drops of rubber solution are formed in the polystyrene solution; however, these drops of rubber solution, for their part, firmly enclose smaller droplets of what has now become the continuous polystyrene phase. At the same time, a grafting of the rubber by polystyrene chains takes place during this polymerization. As a rule, the poly-merization is carried out in several stages. In the first polymeri-zation stage, i.e. the prepolymerization, the solution of rubber in styrene is polymerized, whllst exposed to shear, until a conver-sion beyond the phase inversion point is reached, and thereafter polymerization is continued, to the desired conversion of styrene, under reduced shear or entirely without shear. Continuous mass poly-merlzation or solution polymerization is described, for example, in U.S. Patents 2,694,692, 3,243,481 and 3,658,946. Batchwise combined mass/suspension polymerization is disclosed, for example, in U.S. Patent 3,428,712.
In all these polymerization processes, shearing the reaction mixture in the first process stage, ie. during the prepolymerizationJ
ls of particular importance~ As is known, for example, from U.S. Patent 3,243,481 and British Patent 1,005,681, the particle size of the disperse soft-component phase is brought to a suitable value, during this prepolymerization, by means of the field of shear forces generated by suitable stirring devices; this particle size is a factor of the greatest importance to the mechanical pro-perties of the resulting polystyrene of improved impact strength.
Since the distribution of the disperse soft-component phase can only take place after the phase inversion, the shearing of the poly-merization mixture immediately after phase inversion is a deciding ~ ~c3~ ~ O.Z. 31,926 factor in ad~u~ting the particle size of the disperse soft-component phase. For this reason, the prepolymerization is as a rule taken to a styrene conversion equivalent to from 1.2 to 2 times the amount o~ rubber employed. Shearing far beyond the phase inverslon, ie. up to a conversion corresponding to more than twice the amount of rubber employed, has no significant influence on the particle size of the disperse soft-component phase and is therefore generally not customaryO In addition, the properties of the styrene polymers of improved impact strength can be influenced and varied during the polymerization, for example by using molecular weight regulators or special catalystsO
The styrene polymers, modified to improve their impact strength, which have been manufactured by these conventional processes thus consist of two phases, namely a homogeneous continuous phase (matrix) of the styrene polymer, in which rubbery particles of the soft component are embedded as the disperse phase. The soft com-ponent consists of styrene-grafted rubber particles which contain a greater or lesser amount of occluded matrix material. In the case o~ styrene polymers of high impact strength which have been optimized in respect of mechanical properties, the scatter in particle size of the disperse soft-component phase, expressed in terms of the diameter, in accordance ~lth Appl.Polymer Symposia 15 (1970) page 74 (d), is from 1 to 5/um, and the mean value, ie. the optimum diameter, is thus 3/um.
Because of the incompatibility of the rubber phase with the matrix material and because of the size of the rubber particles ln the disperse soft-component phase, the styrene polymers of high impact strength, and utensils manufactured therefrom, are cloudy and opaque, so that they are unsuitable, or only partially suitable, ~or use in certain fields where a certain degree of transparency is desired, for example the packaglng field. It is, therefore, of interest to provide styrene polymers of high impact strength which, in addition to the conventional good mechanical properties, exhibit .4~ 0.z. ~1,926 a certaln transparency, ie. are at least translucent.
It has been disclosed that the transparency of thermoplastlc polymers which have been modified to improve their impact strength can be improved by matching the refractive lndlces of the hard component and soft component, for example by copolymerizatlon wlth sultable monomers, eg. methyl methacrylate. However, thls measure fundamentally alters the pattern of properties of such molding compositions, eg. the solvent resistance, the melt flow, the soften-ing range or the mechanical properties. This method of lmprovlng the transparency is therefore unsultable ln cases where the fleld of use demands a certain pattern of properties of the styrene poly-mers whlch have been modlfled to lmprove their lmpact strength, for example the comblnation of rigldity and toughness requlred for use ln the packaglng field.
It has also been dlsclosed that the transparency of two-phase systems can be lmproved by lowerlng the partlcle slze of the dls-perse phase to below the wavelength of vlsible llght. However, by merely reduclng the diameter of the rubber partlcles of the dlsperse soft component phase by appropriate technologlcal methods ln the conventlonal processes for the manufacture of polystyrene of high lmpact strength lt ls again not possible to lmprove the transparency wlthout greatly detracting from the mechanlcal propertles.
It ls an object of the present invention to provide a process which permits the manufacture of styrene polymers which have been modified wlth rubber to improve thelr impact strength, and whlch exhlblt not only good mechanical properties but also lmproved transparency. The mechanlcal propertles of the products should sub-stantlally correspond to the styrene polymers of high lmpact strength manufactured by conventlonal processes, and the products should be at least translucent ln thln layers.
We have found, suprlsingly, that this object ls achleved and that such products are obtained if, during the polymerizatlon of styrene ln the presence of the rubber, the shearlng during the prepolymerizatioll is carried ollL in a specific manner and the disperse soft-component phase llas a particular defined composition after phasc inversion at a particular conversion.
Accordingly, the present invention relates to a process for the manufacture of a styrene polymer modified with ~rubber to improve its impact strength, by polymerizing styrene in the presence of 1 to 20~ by weight, based on styrene, of rubber in at least two stages, wherein, in a first stage, the styrene, which contains the rubber in solution, is prepolymerized at from 50 to 150C in the presence or absence of inert diluents, while breaking up the disperse soft-component phase which forms during the polymerization by shearing the polymerization mixture until the quantity of styrene converted, based on the starting solution to be polymerized, corresponds to from 3 to 10 times the amount of elastomer constituent of the total amount of rubber employed and the particles of the disperse soft component phase thus formed have a mean diameter of less than 6 ,um, and thereafter, in one or more further stages, the polymerization is completed by tak~ng it to the desired conversion with reduced shearing or entirely with~out shearing, in mass, in solution or in aqueous suspension. The process of the invention is characterized in that the shearing during prepolymerization is carried out in : such a way that the particles have a weight-average mean diameter of less than 1 ym and a narrow particle-size distribution, and the disperse soft-component phase contains, during the prepolymer-ization, from 35 to 65~ by weight of free or chemically bonded polystyrene segments being incorporated into the rubber component in a chemically bonded form as a polymer block or a grafted branch, the segments having a number-average molecular weight of at least 30,000.
Rubbers which can be employed in the process according to the invention are the natural or synthetic rubbers conventionally used for modifying styrene polymers to improve '~.
1~~
their impact strenc3th. Suitable rubbers are not only natural rubber but also, for example, polybutadiene, polyisoprene and copolymers of butadiene and isoprene with one another or with styrene and/or other comonomers, these copolymers preferably having a glass transition temperature below -20C. The rubbery copolymers of butadiene and/or isoprene may contain the monomers either in random distribution or as blocks. Further suitable rubber components for the process according to the invention for the manufacture of styrene polymers which have been modified to improve their impact strength are rubbery ethylene-propylene copolymers and ethylene-propylene-diene terpolymers.
The elastomer constituent of a rubber is to be understood as the total amount of the rubber minus any chemically bonded constituent comprising a glassy thermoplastic, eg. poly-styrene, in, for example, the form of blocks or grafted branches.
The elastomer content of a styrene-butadiene block copolymer containing 30% of polystyrene blocks is accordingly 70~. This - applies even if, over and above the 30~ of polystyrene blocks, the polybutadiene constituent contains further styrene units in random distribution.
The preferred rubber to use is a homopolymer of a conjugated diene of 4 to 6 carbon atoms, especially polybutadiene.
Elastomeric styrene-diene block copolymers or styrene-diene graft copolymers are equally suitable. The graft copolymers contain polystyrene side branches grafted onto a polydiene, preferably polybutadiene, as the substrate. In the block copolymers, the transition between the individual blocks may be sharp or blurred;
in particular, block copolymers of the general formula A-B or A-B-A may be used. In these formulae, A is a homopolystyrene block and B a homopolymer C~
0,Z. 31,926 block of a con~ugated dlene of 4 to 6 carbon atoms, especlally butadiene, or a copolymer block of a con~ugated dlene, especially butadlene~ with styrene, with random distributlon of the monomers.
The rubbers may be used indlvidually or as mixtures wlth one an-other. The total amount of rubber employed should, however, at most contain 55 per cent by weight of homopolystyrene segments in the form of blocks.
To carry out the process according to the invention, the rubber is first dissolved in the monomeric styrene, and this start-ing solution is then polymerized. In general, the rubber component ls employed in amounts of from 1 to 20 per cent by weight, prefer-ably in amounts of from 2 to 15 per cent by weight, based on the starting solutlon to be polymerized.
The starting solution is polymerized in at least two stages;
in the first stage the monomeric styrene, which contains the rubber in solution, ls prepolymerized in mass or in solution, under the action of shearing forces, and thereafter the polymerization is completed in one or more subsequent stages, under reduced shear or entirely without shear, in mass, solution or aqueous suspension.
The prepolymerization in the first process stage is carried out at from 50 to 150C. The polymerization can be started thermally or by means of initiators which form free radicals. In the case of mass polymerization, the monomeric styrene, containing the rubber in solution, is polymerized directly; in the case of solution poly-merization, up to at most 50 per cent by weight, preferably up to ~0 per cent by weight, based on monomeric styrene employed, of an inert diluent are also added to this starting solution. Usually, at least 2 per cent by weight, preferably from 5 to 10 per cent by weight, of the inert diluent, based on the monomeric styrene :~i employed, are used. Examples of suitable inert diluents are aroma-- tic hydrocarbons or mixtures of aromatic hydrocarbons which are liquid at the polymerization temperature. TolueneJ ethylbenzene, the xylenes or mixtures of these compounds are preferred. If appro-O.Z. 31,926 priate, auxlllarles and addltlves, eg. molecular welght regulators, lubrlcants and the like, may be added to the polymerlzatlon batch.
The reactlon mlxture obtalned from the prepolymerlzatlon in the ~irst stage is then ~lnally polymerized to the desired conversion, elther ln mass or in solution, in one or more further stages, suit-ably at up to 200C, or is suspended ln water in the presence of the known conventional water-soluble suspending agents, eg. methyl-cellulose, hydroxypropylcellulose, polyvlnyl alcohol, partially saponified polyvinyl acetates, polyvlnylpyrrolidone and the like, or inorganic dispersing agents, eg. barium sulfate, the suspending or dispersing agents ln general belng employed in amounts of from 0.1 to 5 per cent by weight, based on the organic phase, and is then flnally polymerlzed, as a rule at from 40 to 160C. If the second process stage is carried out ln aqueous suspension, the addition of inert diluents in the flrst process stage is generally dispensed with. In thls combined mass/suspension process the polymerization is usually initlated by adding oil-soluble initiators which decompose to give free radicals, eg. benzoyl peroxide, dicumyl peroxide, di-tert.-butyl peroxide, azodiisobutyronitrile and the like or combi-nations thereof; the prepolymerization can also be started thermally, and in this latter case it ls possible only to add the oil-soluble inltiators ln the second process stage, when carrying out the poly-merlzatlon ln aqueous suspenslon. After completlon of the polymerl-zation, the end productsobtained are worked up in the conventional known manner.
An essential feature of the process according to the invention is how the process is carried out in the first stage, during the prepolymerlzation, which according to the invention should be taken to the point where the amount of styrene converted corresponds to from 3 to 10 tlmes the elastomer constituent of the total amount of rubber employed, these amounts being in each case based on the start-ing solutlon to be polymerized. In order to achieve products having the deslred pattern of properties it is necessary, on the one hand, O.Z. ~1,926 ellberately to adjust the particle slze of the disperse soft-component phase being formed, by the action of an appropriate field of shearing forces, whilst on the other hand the reaction conditions must be balanced so that at the same time the disperse soft-component phase has a specific composition in this range of conversion. Soft component, for the purposes of the present invention, means the constituent which is toluene-insoluble at room temperature (25C), of the polymer which has been modified to improve its impact strength, minus any pigments which may be present. Accord-ingly, the soft component corresponds to the gel content of the pro-duct and consists, as has been explained at the outset, both of the grafted rubber component and of the part of the matrix material (polystyrene) which has been mechanically included in the grafted rubber particles.
The action of shearing forces on the reaction mixture in the first process stage, in order to break up the disperse soft-component phase after phase inversion, is maintained, according to the invention, until the amount of styrene converted corresponds to from ~ to 10 times the elastomer constituent of the total amount of rubber employed, the amounts in each case being based on the starting solution to be polymerized. The shearing of the polymeriza-tion mixture can be achieved in the conventional manner, by appro-priate stirring devices. The particle size of the disperse soft-component phase depends on the rate of stirring, ie. on the shear-ing stress; the higher the latter, the lower the particle size. The relation between rate of stirring and size and distribution of the disperse soft-component particles formed is in itself known and is described, for example, in U.S. Patent ~,24~,481 or by Freeguard, British Polymer Journal 6 (1974), 205 to 228. According to the inven-tion, the shearing should be carried out so that subsequently the particles of the disperse soft-component phase have a welght-average mean diameter of less than l/um together with a narrow particle size distribution. In general, the weight-average mean particle _g_ 4 ~
O.Z. ~1,926 diameter of the particles of the soft-component phase should be from 0.05 to l/um, preferably from 0.2 to 0.6/um. With larger particle diameters, the translucency of the products progressively decreases. The mean particle diameter of the rubber particles of the disperse soft-component phase can be determined, for example, by counting and evaluating electromicrographs of thin layers (cf.
F. Lenz, Zeitschrift fur Wiss. Mikroskopie 6~ (1956), 50-56). The rate of stirring required to achieve the desired particle size depends, inter alia, on the details of the particular apparatus and is known to those skilled in the art or can be established by a few simple experiments.
A further essential feature of the process according to the invention is that, in addition to maintaining the shearing condi-tions in the first process stage, the first process stage must be controlled so that the disperse soft-component phase contains -when the amount of styrene converted is from ~ to 10 times the elastomer constituent of the total amount of rubber employed, the amount being in each case based on the starting solution to be poly-merized - a total of from ~5 to 65 per cent by weight of polystyrene in the form of chemically bonded blocks or grafted branches or at times also as free homopolymer in an emulsified form.
At least 50 per cent by weight of this polystyrene component which ls requlred to be present in the total disperse soft-component phase at the stated conversion must, however, be contalned as chemically bonded polystyrene segments ln the rubber component and must have a number-average molecular welght cf at least 30,000, preferably at least 50,000. The number-average molecular weight of the polystyrene segments of the soft component which are present chemically bonded as a polymer block or grafted branch in the rubber is in general less than 250,000, preferably less than 150,000. The total homopolystyrene content of the disperse soft component can be determined on a sample, taken from the reaction mixture at the appropriate conversion, by means of the conventional analytical ~ O.Z. 31,926 methods, for example by IR spectroscopy. The chemically bonded content of polystyrene segments in the soft component is determined on rubbers containing polybutadiene by flrst extracting free homo-polystyrene with a mixture of methyl ethyl ketone and acetone and then degrading the polybutadiene part of the residual material by means of OSO4 (see, eg. G. Locatelli and G. Riess, Die Angew.
Makrom. Chem. 26 (1972), pages 117-127).
The polystyrene content in the disperse soft-component phase, at a styrene conversion within the stated range, may be adjusted in various ways, and may, for example, be controlled by the polymeriza-tlon temperature, the amount and nature of the initiators, the presence or absence of molecular weight regulators and the like. It depends, in particular, on the nature of the rubber component emp~yRd.
If, for example, the process according to the invention employs a rubber which does not contain any homopolystyrene segments in the form of blocks, such as, for example, a homopolymer of a conjugated diene, especially polybutadiene, it is necessary, in order to achieve the desired composition of the soft component, to carry out the prepolymerization in the first process stage under conditions which favor the grafting of the styrene onto the rubber. In that case, the prepolymerization is not carried out under the conven-tional conditions, thermally or in the presence of initiators at low temperatures; instead, the polymerization in the first process stage is carried out at relatively high temperatures in the presence of initiators which form free radicals, especially initiators which are known to favor grafting. The choice of the polymerization tem-perature depends above all on the inltiator employed; in general,the temperature ls above 100C. In such a case, the prepolymerization is generally carried out at temperatures such that the half-life of the free radical initiator employed, at the polymerization tempera-ture and in the polymerization solution, is less than 30 minutes, preferably less than 5 minutes. The concentratlon of the initiator is from 0.001 to 1.0 mole per cent, preferably from 0.005 to 0.5 ~ O.Z. 31,926 mole per cent, based on the amount of monomerlc styrene employed.
The conventional lnltiators, eg. alkyl peroxides, acyl peroxides, hydroperoxides, peresters, peroxycarbonates, azo compounds and the like, can be employed; lnitiators which favor grafting, eg.
benzoyl peroxide, are preferred. The decomposition of the initia-tors can also be accelerated by suitable additives or appropriate measures.
The procedure ~ust described is applicable not only when using rubbers consisting of homopolymers of con~ugated dienes, but is in principle applicable in the same manner to all rubbers which do not contain styrene and to rubbery copolymers of a con~ugated diene, especially butadiene, with styrene, in which the monomer units are distributed at random. In this process it is also possible to employ block copolymers or graft copolymers of a conjugated diene, especially butadieneJ with styrene, provided the block polystyrene content of the copolymer, ie. the proportion of polystyrene segments present as polymer blocks or grafted branches ln the copolymer, is less than 25 per cent by weight, based on the block or graft copoly-mer; lf this is not the case, there is the risk that the polystyrene content of the disperse soft-component phase may, during the prepoly-merization, be above the limiting value admissible according to the lnvention, in which case products having the desired pattern of pro-perties would no longer be obtained~
When using a block copolymer or graft copolymer of butadiene and styrene which has a block polystyrene content of from lO to 40 per cent by weight, and in which the number-average molecular weight of these block polystyrene segments is more than ~0,000, preferably more than 50,000, as the rubber, the content of polystyrene segments in the disperse soft-component phase within the stated range of conversion of the monomeric styrene can also be brought to the value of from ~5 to 65 per cent by weight, required according to the inven-tion, by adding to the starting solution, to be polymerized, of this blook copolymer or graft copolymer in monomeric styrene, a homopoly-O.Z. ~1,926 styrene whlch has a molecular weight equal to or lower than themolecular weight of the block polystyrene segments ln the block copolymer or graft copolymer. The prepolymerization of the starting solution can then be carried out, in respect of temperature control and catalyst addition, under the conventional conditions normally employed for the manufacture of styrene polymers which have been modified to improve their impact strength. During the polymerization, the homopolystyrene added to the starting solution is incorporated lnto the polystyrene domains of the butadlene/styrene block copoly-mers or graft copolymers and is thus ultimately contained in the disperse soft-component phase, thereby increasing its content of bonded or emulsified polystyrene. The amount of homopolystyrene which is additionally introduced into the starting solution, to be polymerized, of the block copolymer or graft copolymer in monomeric styrene depends on the block polystyrene content of the block co-polymer or graft copolymer used. It must be so chosen that the sum of the block polystyrene content of the block copolymer or graft copolymer and the additionally introduced homopolystyrene is at least 20 per cent by weight, preferably at least 25 per cent by weight, and at most 55 per cent by weight, preferably at most 50 per cent by weight, in each case based on the sum of block copolymer or graft copolymer and additionally lntroduced homopolystyrene.
Further, it is possible to obtain the required content of poly-styrene segments in the disperse soft-component phase by employing, as the rubber, a block copolymer or graft copolymer of a con~ugated dlene, especially butadlene, and styrene, which contalns from 25 to 55 per cent by weight, based on the block copolymer or graft copoly-mer, of polystyrene blocks and in which the number-average molecular weight of the block polystyrene segments is at least 30,000, prefer-ably at least 50,000. The number-average molecular weight of the block polystyrene segments is in general less than 250,000, prefer-ably less than 150,000. If block copolymers with a blurred transi-tion between the polydlene blocks and the polystyrene blocks are -1,~-~ O.Z. ~1,926 used, the transitlon range must be lncluded, for calculatlon purposes, wlth the polydiene block, le. with the elastomer constltuent of the rubber, so that only the pure homopolystyrene segments are treated as the polystyrene block constltuent. The prepolymerization ln the first process stage can ln this case be carried out under the con-ventlonal conditlons in respect of temperature regime and of cata-lyst employed, since, under these condltions, sufflcient polystyrene ls grafted onto the rubber component and is occluded by the rubber particles durlng phase inverslon to give a total content of poly-styrene segments, contained in the disperse soft-component phase in the critical range of conversion of the monomeric styrene, of from 35 to 65 per cent by weight, based on the total disperse soft-component phase at this conversion. If block copolymers or graft copolymers of conjugated dienes and styrene having a high block polystyrene content) of more than 55 per cent by weight, based on the block copolymer or graft copolymer, are employed, the proportion of polystyrene segments ln the disperse soft-component phase at the converslon in question ls always above the range requlred according to the in~ention, and accordingly products havlng lmproved trans-parency are not obtalned.
Such elastomerlc block copolymers or graft copolymers of con-~ugated dienes and styrene, having~ high content of block polystyrene, above from about 50 to 55 per cent by weight, can however be used as the rubber in the process accordlng to the lnventlon if they are employed as a mixture with a homopolymer of the corr~sponding con-jugated dlene. Thls mixture of block copolymer or graft copolymer and homopolymer of the conjugated diene then forms the total rubber component. The proportlon of homopolymer of the conjugated diene in this mixture depends on the block polystyrene conten~ of the block copolymer or graft copolymer and is so chosen that the proportion of block polystyrene in the rubber mixture employed is at least 20 per cent by weight, preferably at least 25 per cent by weight and at most 55 per cent by weight, preferably at most 50 per cent by O.Z. ~1,926 welght, based on the rubber mlxture. The proportlon of the homopoly-mer of the conJugated dlene ln the total rubber mlxture should, however, ln general not exceed 50 per cent by welghtJ based on the rubber mixture. We have found that such a rubber mlxture behaves ln the process as lf it were a block copolymer or graft copolymer havlng a correspondlng content of block polystyrene and accordlngly can be used under the same condltions as the latter ln the process accordlng to the lnvention.
It ls also possible to add a molecular welght regulator durlng the prepolymerlzation (started thermally or by means of lnltlators whlch form free radlcals) of the starting solution, in order thereby to control the proportion of polystyrene grafted onto the rubber, and the molecular welght Or the polystyrene, ln accordance wlth the lnventlon. The molecular welght regulator, the transfer constant of whlch should be at least 1, preferably from 2 to 15, under the reac-tlon conditions is added, preferably ln amounts of at least 0.1 per cent by weight, based on the monomeric styrene employed, to the . .
starting solution at the beginnlng of> or durlng, the prepolymerlza-~; i tlon, prior to the phase lnverslonO
In general, lt can be stated that the prepolymerlzation ln the first stage of the process can be carrled out ln prlnclple ln any deslred manner, provided the two conditlons according to the inven-tion, namely those relating to the shearing of the polymerlzation mlxture and to the composition of the disperse soft-component phase, are fulfllled. The manner ln whlch the polymerlzation is completed ln the second process stage and possibly further process stages ls not essentlal to the lnventlon. As has already been descrlbed, thls flnal polymerization ls carried out in mass, in solution or in aqueous suspension and employs the conventional procedures, such as are described, for example, in the publication cited lnitlally, whlch are hereln lncorporated by reference.
The styrene polymers modlfled to lmprove thelr lmpact strength, which are manufactured ln accordance with the lnventlon have improved :
~ ~ ~4~ O.Z. 31,926 transparency compared to conventional polystyreneswhich have been modified to improve their impact strength, ie. they are translucent and even transparent in thin layers, without this improvement being accompanied by a deterioration of the level of mechanical proper-ties of the materials compared to comparable conventlonal products which are not translucent. In addition, finished articles made from the products manufactured according to the invention exhibit a high gloss. The styrene polymers,which have been modified to improve their impact strength, obtained in accordance with the present in-vention are therefore particularly suitable for use in the packaging field. When used for this purpose, they may contain the conventional additives and auxiliaries.
The Examples which follow illustrate the invention. Parts and percentages are by weight, unless stated otherwise. The products are tested in accordance with the following methods:
1. Yield stress (N/mm2) and tensile strength (N/mm2) were deter-mined on a molded dumbbell-shaped bar according to DIN 5~,455.
2. Notched impact strength (kJ/m ): DIN draft based on the decision of the German Special Standards Committee for Plastics 4.~ of March 1975, in preparation.
3. The weight-average mean particle size of the disperse soft-component phase was determined by counting and averaging the particles belonging to the same size category (constant interval width), using thin layer electromicrographs. The cumulative distri-bution curve i5 determined from the volumes of the particles (~rd power of the apparent diameter) within the various intervals. The equivalent diameter can then be read off on the abscissa at the point corresponding to the 50~ ordinate value. The mean diameters quoted represent a mean value for at least 5JOOO particles.
4. The transparency was assessed visually on molded round discs of 1 mm thickness and 60 mm diameter.
COMPARATIVE EXAMPLE A
A 4% strength solution of polybutadiene (molecular weight ~ O,Z. ~1,926 180,000; 1,2-vinyl content = 10%) in styrene was mlxed wlth o,o88 mole per cent (based on styrene) of benzoyl peroxlde and was pre-polymerized, whilst stirring, in a reaction kettle, at 80C, to give a solids content of 36~ (- 3~.3% styrene conversion). 0.1 per cent by weight (based on polybutadiene + styrene) of dicumyl peroxide was then dissolved in the polymer solution. A 3-fold amount of water, containing o.64 per cent by weight of sodium carboxy-methylcellulose as the protective colloid was then added and the polymer solution was suspended therein. The reaction batch was then polymerized to a solids content of ~99%, with continued stirring, over 5 hours at 120C and 5 hours at 140C.
The polystyrene of high impact strength, thus obtained, is cloudy and opaque. The particles of the soft component have a mean diameter of about 4/um. The properties are shown in Table 1.
The same batch as that used in Comparative Example A was heated, whilst stirring. The heat liberated when the polymerization starts was lnitially not removed, ie. the polymerization was carried out adiabatically; in the course of a few minutes, the temperature of the polymerization batch rose to 140C. The batch was then cooled intensively and its temperature lowered to 70-80C. After the prepoly-merization, the solids content was 36.5% (~ ~3.9% styrene conver-sion). 0.1 per cent by welght (based on the amount of polybutadiene + styrene) of dicumyl peroxide was then added and after addition of the aqueous phase the polymerization was completed as described ln Comparative Example A. The resulting polystyrene of high impact strength is very translucent, and even transparent as a thin layer.
The particles of the disperse soft-component phase have a diameter of 5 0.5/um. The properties are shown in Table 1.
COMPARATIVE EXAMPLE B
A mixture of 4 parts of polybutadiene, 6 parts of ethylbenzene a~d 90 parts of styrene was mixed with 0.04 mole per cent (based on styrene) of benzoyl peroxide and prepolymerized continuously in a .~ .
~ 4~4 o.z. 31,926 tubular reactor at about 75C/ to give a sollds content Or 6.5~
(- 2.8% styrene converslon). The polymer solutlon was then poly-merlzed, as part Or the prepolymerizatlon process, to 41.8~ sollds content ln an apparatus as described ln German Lald-Open Applica-tlon DOS 1, 770,392 and then polymerized to a solids content Or 79~
(_ 83.3% styrene conversion); rinally, the residual styrene and the solvent were distllled off under reduced pressure at above the softening polnt of polystyrene. The polystyrene melt was forced through a die and the strand which issued was granulatedO The resulting polystyrene of high impact strength (polybutadiene content = 6%) was opaque. The disperse soft-component phase was in the form of particles having a diameter Or from about 2 to about 5/um.
If higher solids contents were achieved in the prepolymeriza-tion in the tubular reactor, there was no fundamental change in the pattern Or properties (compare Table 1).
The same mixture as in Comparative Example B was prepolymerized in the tubular reactor, at about 130C, to a solids content of 17%
(- 14.4% styrene conversion). The final polymerization and working up were carried out as described in Comparative Example B.
The resulting polystyrene of high impact strength (polybutadiene content = 6~ ~ is very translucent, and even transparent in thin layers. The soft-component phase has a particle size Or rrom o.3 to O .5/um-Example/Comparative Example A 1 B 2 Polystyrene content Or the soft 28.6 39.4 26.9 40.8 component, %
Styrene converted/elastomer con- 8 o 8 13 9 45 9 45 stituent of the rubber Yield stress (N-mm2) 32.3 36.3 28.3 31-9 Notch lmpact strength (kJ/m2) 7-9 7.1 11.2 10.1 Translucency - + _ +
M (polystyrene from the soft-component p~ase at the end of the prepolymcri7.ation): 70,000 54,000 110,000 83,000 ~$~4~ o . z . 31,926 In the Examplcs which follow, ~he products shown below were used as rubbers:
Wl: Bu/S block copolymer with a blurred transition between the blocks: [~] = 1.51 (dl/g) (toluene, 25);
Block PS = 24.4~; r~= 0.264 (dl/g) (toluene, 25);
Total styrene content = 41.0%, M (BlockPS)=44,000; M = 24,000, W2: Bu/S block copolymer with a blurred transition between the blocks: ~ = 1.76 (dl/g) (toluene 25);
Block PS = 27.7~; [~ = o.3~4 (dl/g) (toluene, 25 );
Total styrene content = 41.0~; MV - 61,000; Mn = 33~000.
W3: Bu/S block copolymer with a blurred transition between the blocks: [~ ] = 1.74 (dl/g) (toluene, 25~;
Block PS = 31-0%; r~] = oO364 (dl/g) (toluene, 25c);
Total styrene content = 41.6%~ MV ~ 67,000;- Mn = 36,000.
w4: Bu/S block copolymer with a blurred transition between the blocks: r~ ] = 1 58 ( dl/g) (toluene 250);
Block PS = 39-4~; r~ = 0.4~o (dl/g) (toluene, 25);
Total styrene content = 40.5%P MV - 98,000; M = 53,000, w5: Bu/S block copolymer with sharply separated blocks:
[~ = 1.64 (dl/g) (toluene, 25);
Block PS = 32-4%; r~] = o-337 (dl/g) (toluene, 25);
Total styrene content = 32.4%. ~ = 62,000; Mn = 33~000.
W6: Bu/S block copolymer with sharply separated blocks:
~] = 2.70 (dl/g) (toluene, 25);
Block PS - 70%; [~ = 1.67 (dl/g) (toluene, 25);
Total styrene content = 70~; Mv= 590,000; M - 320,000.
Bu: butadiene S: styrene PS: polystyrene [~]: lntrinsic viscosity, measured in toluene at 25C.
The polystyrene of high impact strength was manufactured . batchwise by mass/suspension polymerization. The results are shown in Tables 2 and ~.
.
~$i~ o.z. ~1,9~6 COi~lPAI~ATIVE EXA~I~L~ C
A solutlon consistlng Or 1,560 g o~ styrene, 240 g of W~, 1.6 g of t-dodecylmercaptan, 2.2 g of Irganox 1076 and 1.7 g Or dicumyl peroxide was prepolymerized at 110C internal temperature in a 5 1 stirred kettle ~ith a blade stlrrer, at a stirrer speed of 150 rpm, until the solids content was 28.7%. Accordingly, the styrene conversion was about 1.7 times the elastomer constituent Or the W~ rubber used.
1,800 ml Or water containing 9.0 g of polyvinylpyrrolidone of K value 90 and 1.8 g of Na4P207 were then added and the stirrer speed was increased to ~00 rpm. The final polymerization was then carried out for 5 hours at 120C and 5 hburs at 140C, giving a styrene conversion of ~99j~.
EXAMPLE ~
The batch, and the reaction conditions, were the same as in Comparative Example C, except that the prepolymerization was taken to a solids content Or 43.8%, whilst stirring, and the aqueous phase was only added then. This corresponds to a styrene conversion whlch is about ~.~ times the elastomer constituent of the W~ rubber used.
In contrast to Example 3, W4 was used as the rubber. The solids content after the prepolymerization was 49.7~; this corresponds to a styrene conversion of about 4.5 times the elastomer constituent of the W5 rubber used.
COMPARATIVE EXAMPLE D
A solution consisting of 1,260 g of styrene, 201 g of W5, ~7 g of mineral oil as the lubricant, 1.5 g of t-dodecylmercaptan, 1.~ g of IR~AN~X 1076 and 1.6 g of dicumyl peroxide was prepoly-merized at 115C internal temperature in a 5 1 stirred kettle with a blade stirrer, at a stirrer speed of 200 rpm, until the solids content was 34.2~. Accordingly, the styrene conversion was about 2.3 times the eIastomer constituent of the W5 rubber used.
* Trademark -20-~' :, ' , .
,C!~ 0.~. 31,~26 The aqueous pllase and the post-polymcrization conditions correspond to the data in Comparatlve Example C.
The same batch as in Comparative Example D was prepolymerized under the same conditions, to a solids content o~ 47.6%. According-ly, the styrene conversion was about 3.8 times the elastomer consti-tuent of the W5 rubber used.
A solution consisting Or 1,605 g of styrene, 150 g Of W4~ 45 g Or mineral oil, 1.8 g of t-dodecylmercaptan, 2.2 g Of IRGAN~X 1076 and 1.8 g o~ dicumyl peroxide was prepolymerized at 115C internal temperature in a 5 1 stirred kettle with a blade stirrer, at a stirrer speed of 200 rpm, until the solids content was 46.5~.
Accordingly, the styrene conversion was about 6.6 times the elastomer constituent of the W4 rubber used.
The aqueous phase, and the post-polymerization details, were - as in Comparative Example C.
: COMPARATIVE EXAMPLE E
A solution consisting of 1~600 g O~ styrene, 200 g Or Wl, 1.8 g of t-dodecylmercaptan, 2.2 g of IKGANOX 1076 and 1.8 g Or dicumyl peroxide was prepolymerized at 115C internal temperature in a 5 1 stirred kettle with a blade stirrer, at a stirrer speed of 200 rpm, until the solids content was 43.2%. Accordingly, the styrene conver-sion was about 3.8 times the elastomer constituent of the Wl rubber used.
The aqueous phase, and the post-polymerization details, were ~ as in Comparative Example C.
0.3%, based on styrene, of benzoyl peroxide was added, to act as a starter which ravors grarting, to the same reaction batch as that described in Comparative Example E.
Prepolymerization was carrled out at from 80 to 85C and a stirrer speed of 200 rpm, until the solids content was 42.9,o.
- 21 ~
4~
O.Z. ~1,926 Accordlngly, the styrene conversion was abou~ 4.2 times the elastome constltuent Or the Wl rubber used. The aqueous phase, and the post-polymerization detalls, ~ere as in Comparatlve Example C.
EXAMPLE ~
A solution consisting Or 1,600 g Or styrene, 170 g of Wl, 30 g of polystyrene with L~ = 0.252 (dl/g) in toluene, 1.8 g of t-dodecylmercaptan, 2.2 g of IRGANOX 1076 and 1.8 g of dicumyl peroxide was prepolymerized at 115C internal temperature in a 5 1 stlrred kettle with a blade stirrer, at a stirrer speed of 200 rpm, until the solids content was 43~1%. Accordingly, the styrene conversion was about 4.5 times the sume of the Wl rubber component used and the polystyrene used. Assuming that the added polystyrene is completely taken up in the polystyrene domains of Wl, the "block" polystyrene content of Wl is altered from 24.4~ to 35.7%.
The aqueous phase, and the post-polymerization details, were as in Comparative Example C.
A solution consisting of 1,605 g of styrene, 120 g of W4, ~0 g of polybutadiene (molecular weight ~ 200,000; 1,2-vinyl content ~ 10%), 45 g of mineral oil, 1.8 g of t-dodecylmercaptan, 2.2 g of IRGANO~ 1076 and 1.8 g of dicumyl peroxide was prepolymerized at 115C internal temperature in a 5 1 stirred kettle with a blade stirrer, at a stirrer speed of 200 rpm, until the solids content was ~8.9~. Accordingly, the styrene conversion was about 5.4 times the sume of the elastomer constituent in the W4 rubber used and the polybutadiene used. Assuming that the added polybutadiene is completely taken up in the polybutadiene domains of W4, the block polystyrene content Or w4 is altered from 39.4~ to ~1.5%.
The aqueous phase, and the post-polymerization details, were as in Comparative Example C.
A solution consisting of 1,650 g of styrene, 75 g of W6, O.Z. ~1,926 75 g Or polybutadiene (as in Example 9), 1.8 g Or t-dodecylmercaptan, 2.2 g Or I~ ox 1076 and 1.8 ~ Or dicumyl peroxlde was prepoly-merized at 115 C internal temperature ln a 5 1 stlrred kettle wlth a blade stirrer, at a stirrer speed Or 200 rpm, until the solids content was 39.2~. Accordingly, the styrene conversion was about
COMPARATIVE EXAMPLE A
A 4% strength solution of polybutadiene (molecular weight ~ O,Z. ~1,926 180,000; 1,2-vinyl content = 10%) in styrene was mlxed wlth o,o88 mole per cent (based on styrene) of benzoyl peroxlde and was pre-polymerized, whilst stirring, in a reaction kettle, at 80C, to give a solids content of 36~ (- 3~.3% styrene conversion). 0.1 per cent by weight (based on polybutadiene + styrene) of dicumyl peroxide was then dissolved in the polymer solution. A 3-fold amount of water, containing o.64 per cent by weight of sodium carboxy-methylcellulose as the protective colloid was then added and the polymer solution was suspended therein. The reaction batch was then polymerized to a solids content of ~99%, with continued stirring, over 5 hours at 120C and 5 hours at 140C.
The polystyrene of high impact strength, thus obtained, is cloudy and opaque. The particles of the soft component have a mean diameter of about 4/um. The properties are shown in Table 1.
The same batch as that used in Comparative Example A was heated, whilst stirring. The heat liberated when the polymerization starts was lnitially not removed, ie. the polymerization was carried out adiabatically; in the course of a few minutes, the temperature of the polymerization batch rose to 140C. The batch was then cooled intensively and its temperature lowered to 70-80C. After the prepoly-merization, the solids content was 36.5% (~ ~3.9% styrene conver-sion). 0.1 per cent by welght (based on the amount of polybutadiene + styrene) of dicumyl peroxide was then added and after addition of the aqueous phase the polymerization was completed as described ln Comparative Example A. The resulting polystyrene of high impact strength is very translucent, and even transparent as a thin layer.
The particles of the disperse soft-component phase have a diameter of 5 0.5/um. The properties are shown in Table 1.
COMPARATIVE EXAMPLE B
A mixture of 4 parts of polybutadiene, 6 parts of ethylbenzene a~d 90 parts of styrene was mixed with 0.04 mole per cent (based on styrene) of benzoyl peroxide and prepolymerized continuously in a .~ .
~ 4~4 o.z. 31,926 tubular reactor at about 75C/ to give a sollds content Or 6.5~
(- 2.8% styrene converslon). The polymer solutlon was then poly-merlzed, as part Or the prepolymerizatlon process, to 41.8~ sollds content ln an apparatus as described ln German Lald-Open Applica-tlon DOS 1, 770,392 and then polymerized to a solids content Or 79~
(_ 83.3% styrene conversion); rinally, the residual styrene and the solvent were distllled off under reduced pressure at above the softening polnt of polystyrene. The polystyrene melt was forced through a die and the strand which issued was granulatedO The resulting polystyrene of high impact strength (polybutadiene content = 6%) was opaque. The disperse soft-component phase was in the form of particles having a diameter Or from about 2 to about 5/um.
If higher solids contents were achieved in the prepolymeriza-tion in the tubular reactor, there was no fundamental change in the pattern Or properties (compare Table 1).
The same mixture as in Comparative Example B was prepolymerized in the tubular reactor, at about 130C, to a solids content of 17%
(- 14.4% styrene conversion). The final polymerization and working up were carried out as described in Comparative Example B.
The resulting polystyrene of high impact strength (polybutadiene content = 6~ ~ is very translucent, and even transparent in thin layers. The soft-component phase has a particle size Or rrom o.3 to O .5/um-Example/Comparative Example A 1 B 2 Polystyrene content Or the soft 28.6 39.4 26.9 40.8 component, %
Styrene converted/elastomer con- 8 o 8 13 9 45 9 45 stituent of the rubber Yield stress (N-mm2) 32.3 36.3 28.3 31-9 Notch lmpact strength (kJ/m2) 7-9 7.1 11.2 10.1 Translucency - + _ +
M (polystyrene from the soft-component p~ase at the end of the prepolymcri7.ation): 70,000 54,000 110,000 83,000 ~$~4~ o . z . 31,926 In the Examplcs which follow, ~he products shown below were used as rubbers:
Wl: Bu/S block copolymer with a blurred transition between the blocks: [~] = 1.51 (dl/g) (toluene, 25);
Block PS = 24.4~; r~= 0.264 (dl/g) (toluene, 25);
Total styrene content = 41.0%, M (BlockPS)=44,000; M = 24,000, W2: Bu/S block copolymer with a blurred transition between the blocks: ~ = 1.76 (dl/g) (toluene 25);
Block PS = 27.7~; [~ = o.3~4 (dl/g) (toluene, 25 );
Total styrene content = 41.0~; MV - 61,000; Mn = 33~000.
W3: Bu/S block copolymer with a blurred transition between the blocks: [~ ] = 1.74 (dl/g) (toluene, 25~;
Block PS = 31-0%; r~] = oO364 (dl/g) (toluene, 25c);
Total styrene content = 41.6%~ MV ~ 67,000;- Mn = 36,000.
w4: Bu/S block copolymer with a blurred transition between the blocks: r~ ] = 1 58 ( dl/g) (toluene 250);
Block PS = 39-4~; r~ = 0.4~o (dl/g) (toluene, 25);
Total styrene content = 40.5%P MV - 98,000; M = 53,000, w5: Bu/S block copolymer with sharply separated blocks:
[~ = 1.64 (dl/g) (toluene, 25);
Block PS = 32-4%; r~] = o-337 (dl/g) (toluene, 25);
Total styrene content = 32.4%. ~ = 62,000; Mn = 33~000.
W6: Bu/S block copolymer with sharply separated blocks:
~] = 2.70 (dl/g) (toluene, 25);
Block PS - 70%; [~ = 1.67 (dl/g) (toluene, 25);
Total styrene content = 70~; Mv= 590,000; M - 320,000.
Bu: butadiene S: styrene PS: polystyrene [~]: lntrinsic viscosity, measured in toluene at 25C.
The polystyrene of high impact strength was manufactured . batchwise by mass/suspension polymerization. The results are shown in Tables 2 and ~.
.
~$i~ o.z. ~1,9~6 COi~lPAI~ATIVE EXA~I~L~ C
A solutlon consistlng Or 1,560 g o~ styrene, 240 g of W~, 1.6 g of t-dodecylmercaptan, 2.2 g of Irganox 1076 and 1.7 g Or dicumyl peroxide was prepolymerized at 110C internal temperature in a 5 1 stirred kettle ~ith a blade stlrrer, at a stirrer speed of 150 rpm, until the solids content was 28.7%. Accordingly, the styrene conversion was about 1.7 times the elastomer constituent Or the W~ rubber used.
1,800 ml Or water containing 9.0 g of polyvinylpyrrolidone of K value 90 and 1.8 g of Na4P207 were then added and the stirrer speed was increased to ~00 rpm. The final polymerization was then carried out for 5 hours at 120C and 5 hburs at 140C, giving a styrene conversion of ~99j~.
EXAMPLE ~
The batch, and the reaction conditions, were the same as in Comparative Example C, except that the prepolymerization was taken to a solids content Or 43.8%, whilst stirring, and the aqueous phase was only added then. This corresponds to a styrene conversion whlch is about ~.~ times the elastomer constituent of the W~ rubber used.
In contrast to Example 3, W4 was used as the rubber. The solids content after the prepolymerization was 49.7~; this corresponds to a styrene conversion of about 4.5 times the elastomer constituent of the W5 rubber used.
COMPARATIVE EXAMPLE D
A solution consisting of 1,260 g of styrene, 201 g of W5, ~7 g of mineral oil as the lubricant, 1.5 g of t-dodecylmercaptan, 1.~ g of IR~AN~X 1076 and 1.6 g of dicumyl peroxide was prepoly-merized at 115C internal temperature in a 5 1 stirred kettle with a blade stirrer, at a stirrer speed of 200 rpm, until the solids content was 34.2~. Accordingly, the styrene conversion was about 2.3 times the eIastomer constituent of the W5 rubber used.
* Trademark -20-~' :, ' , .
,C!~ 0.~. 31,~26 The aqueous pllase and the post-polymcrization conditions correspond to the data in Comparatlve Example C.
The same batch as in Comparative Example D was prepolymerized under the same conditions, to a solids content o~ 47.6%. According-ly, the styrene conversion was about 3.8 times the elastomer consti-tuent of the W5 rubber used.
A solution consisting Or 1,605 g of styrene, 150 g Of W4~ 45 g Or mineral oil, 1.8 g of t-dodecylmercaptan, 2.2 g Of IRGAN~X 1076 and 1.8 g o~ dicumyl peroxide was prepolymerized at 115C internal temperature in a 5 1 stirred kettle with a blade stirrer, at a stirrer speed of 200 rpm, until the solids content was 46.5~.
Accordingly, the styrene conversion was about 6.6 times the elastomer constituent of the W4 rubber used.
The aqueous phase, and the post-polymerization details, were - as in Comparative Example C.
: COMPARATIVE EXAMPLE E
A solution consisting of 1~600 g O~ styrene, 200 g Or Wl, 1.8 g of t-dodecylmercaptan, 2.2 g of IKGANOX 1076 and 1.8 g Or dicumyl peroxide was prepolymerized at 115C internal temperature in a 5 1 stirred kettle with a blade stirrer, at a stirrer speed of 200 rpm, until the solids content was 43.2%. Accordingly, the styrene conver-sion was about 3.8 times the elastomer constituent of the Wl rubber used.
The aqueous phase, and the post-polymerization details, were ~ as in Comparative Example C.
0.3%, based on styrene, of benzoyl peroxide was added, to act as a starter which ravors grarting, to the same reaction batch as that described in Comparative Example E.
Prepolymerization was carrled out at from 80 to 85C and a stirrer speed of 200 rpm, until the solids content was 42.9,o.
- 21 ~
4~
O.Z. ~1,926 Accordlngly, the styrene conversion was abou~ 4.2 times the elastome constltuent Or the Wl rubber used. The aqueous phase, and the post-polymerization detalls, ~ere as in Comparatlve Example C.
EXAMPLE ~
A solution consisting Or 1,600 g Or styrene, 170 g of Wl, 30 g of polystyrene with L~ = 0.252 (dl/g) in toluene, 1.8 g of t-dodecylmercaptan, 2.2 g of IRGANOX 1076 and 1.8 g of dicumyl peroxide was prepolymerized at 115C internal temperature in a 5 1 stlrred kettle with a blade stirrer, at a stirrer speed of 200 rpm, until the solids content was 43~1%. Accordingly, the styrene conversion was about 4.5 times the sume of the Wl rubber component used and the polystyrene used. Assuming that the added polystyrene is completely taken up in the polystyrene domains of Wl, the "block" polystyrene content of Wl is altered from 24.4~ to 35.7%.
The aqueous phase, and the post-polymerization details, were as in Comparative Example C.
A solution consisting of 1,605 g of styrene, 120 g of W4, ~0 g of polybutadiene (molecular weight ~ 200,000; 1,2-vinyl content ~ 10%), 45 g of mineral oil, 1.8 g of t-dodecylmercaptan, 2.2 g of IRGANO~ 1076 and 1.8 g of dicumyl peroxide was prepolymerized at 115C internal temperature in a 5 1 stirred kettle with a blade stirrer, at a stirrer speed of 200 rpm, until the solids content was ~8.9~. Accordingly, the styrene conversion was about 5.4 times the sume of the elastomer constituent in the W4 rubber used and the polybutadiene used. Assuming that the added polybutadiene is completely taken up in the polybutadiene domains of W4, the block polystyrene content Or w4 is altered from 39.4~ to ~1.5%.
The aqueous phase, and the post-polymerization details, were as in Comparative Example C.
A solution consisting of 1,650 g of styrene, 75 g of W6, O.Z. ~1,926 75 g Or polybutadiene (as in Example 9), 1.8 g Or t-dodecylmercaptan, 2.2 g Or I~ ox 1076 and 1.8 ~ Or dicumyl peroxlde was prepoly-merized at 115 C internal temperature ln a 5 1 stlrred kettle wlth a blade stirrer, at a stirrer speed Or 200 rpm, until the solids content was 39.2~. Accordingly, the styrene conversion was about
5.7 times the sum of the elastomer constituent ln the ~16 rubber used and the polybutadiene used. Assumlng that the added polybuta-diene is completely taken up in the polybutadiene domains Or W6, the block polystyrene content Or W6 ls altered from 70~ to 35%.
The aqueous phase, and the post-polymerization detalls, were as ln Comparatlve Example C.
Example/ Polystyrene in Ratio Or converted Comparatlve Example the soft component styrene to elastomer (~) constituent of the rubber C 44,4 1.68 3 47.4 3.33 . 4 52.4 4.52 D 44.7 2.30 ~8.7 3.79
The aqueous phase, and the post-polymerization detalls, were as ln Comparatlve Example C.
Example/ Polystyrene in Ratio Or converted Comparatlve Example the soft component styrene to elastomer (~) constituent of the rubber C 44,4 1.68 3 47.4 3.33 . 4 52.4 4.52 D 44.7 2.30 ~8.7 3.79
6 52.7 6.56 E 34.5 3.84
7 43.3 3.2~
8 50.2 4.50
9 46.5 5.38 48.9 5.72 : -23-~, z . 31, 926 h I + + I + + I + + + +
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Claims (7)
1. In a process for the manufacture of a styrene polymer modified with rubber to improve its impact strength, by polymerizing styrene in the presence of 1 to 20% by weight, based on styrene, of rubber in at least two stages, wherein, in a first stage, the styrene, which contains the rubber in solution, is prepolymerized at from 50 to 150°C in the presence or absence of inert diluents, while breaking up the disperse soft-component phase which forms during the polymerization by shearing the polymerization mixture until the quantity of styrene converted, based on the starting solution to be polymerized, corresponds to from 3 to 10 times the amount of elastomer constituent of the total amount of rubber employed and the particles of the disperse soft component phase thus formed have a mean diameter of less than 6 µm, and thereafter, in one or more further stages, the polymerization is completed by taking it to the desired conversion with reduced shearing or entirely without shearing, in mass, in solution or in aqueous suspension, the improvement which comprises carrying out the shearing during prepolymerization in such a way that the particles have a weight-average mean diameter of less than 1 µm and a narrow particle-size distribution, and the disperse soft-component phase contains, during the prepolymerization, from 35 to 65% by weight of free or chemically bonded polystyrene segments being incorporated into the rubber component in a chemically bonded form as a polymer block or a grafted branch, said segments having a number-average molecular weight of at least 30,000.
2. A process as claimed in claim 1, wherein the rubber is a homopolymer of a conjugated diene of 4 to 6 carbon atoms.
3. A process as claimed in claim 1, wherein the rubber is employed in an amount of from 2 to 15 per cent by weight based on the starting solution to be polymerized.
4. A process as claimed in claim 1, wherein the polymerization in the first stage is carried out in mass in the absence of inert diluents and the polymerization is completed in one or more stages in aqueous suspension.
5. A process as claimed in claim 1, wherein the whole polymerization is carried out in solution in the presence of an inert diluent.
6. A process as claimed in claim 1, wherein the shearing of the polymerization mixture in the first stage is carried out to provide particles of the disperse soft-component phase having a weight-average mean diameter of from 0.2 to 0.6 µm.
7. A process as claimed in claim 2, wherein the polymerization in the first stage is carried out at a temperature above 100°C such that the half-life of the free radical initiator present is less than 30 minutes under the conditions employed and its concentration is from 0.001 to 1.0 mole per cent based on the amount of monomeric styrene employed whereby the grafting of the styrene onto the rubber is favored.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE2613352A DE2613352B2 (en) | 1976-03-29 | 1976-03-29 | Process for the production of impact-resistant modified styrene polymers |
| DEP2613352.8 | 1976-03-29 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1114984A true CA1114984A (en) | 1981-12-22 |
Family
ID=5973755
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA273,939A Expired CA1114984A (en) | 1976-03-29 | 1977-03-14 | Manufacture of styrene polymers which have been modified to improve their impact strength |
Country Status (11)
| Country | Link |
|---|---|
| US (1) | US4282334A (en) |
| JP (1) | JPS6057443B2 (en) |
| BE (1) | BE852793A (en) |
| CA (1) | CA1114984A (en) |
| DE (1) | DE2613352B2 (en) |
| ES (1) | ES457263A1 (en) |
| FR (1) | FR2346381A1 (en) |
| GB (1) | GB1576772A (en) |
| GR (1) | GR65690B (en) |
| IT (1) | IT1081354B (en) |
| NL (1) | NL7703199A (en) |
Families Citing this family (31)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| ES8103120A1 (en) * | 1979-03-07 | 1981-02-16 | Monsanto Co | Process for the continuous production of polyblends derived from an alkenyl aromatic monomer and a diene rubber. |
| JPS5919576B2 (en) * | 1979-11-01 | 1984-05-07 | 三井東圧化学株式会社 | Manufacturing method of rubber modified styrenic resin |
| DE3018643C2 (en) * | 1980-05-16 | 1982-07-08 | Chemische Werke Hüls AG, 4370 Marl | Process for the production of impact-resistant modified styrene polymers |
| DE3023721A1 (en) | 1980-06-25 | 1982-01-21 | Basf Ag, 6700 Ludwigshafen | METHOD FOR THE CONTINUOUS PRODUCTION OF RUBBER-MODIFIED POLYMERISATS OF VINYL FLAVORS |
| DE3032260A1 (en) * | 1980-08-27 | 1982-04-08 | Basf Ag, 6700 Ludwigshafen | PROCESS FOR THE CONTINUOUS PRODUCTION OF RUBBER-MODIFIED POLYMERISATS OF VINYLAROMATS, USE THEREOF FOR INJECTION MOLDING AND MOLDED PARTS FROM THESE POLYMERISATES |
| JPS5796006A (en) * | 1980-12-05 | 1982-06-15 | Mitsui Toatsu Chem Inc | Production of rubber-modified styrene resin |
| DE3047293A1 (en) * | 1980-12-16 | 1982-07-29 | Basf Ag, 6700 Ludwigshafen | METHOD FOR PRODUCING ABS POLYMERISATES, USE THEREOF, AND MOLDED PARTS THEREOF |
| DE3409656A1 (en) * | 1984-03-16 | 1985-09-19 | Basf Ag, 6700 Ludwigshafen | METHOD FOR PRODUCING TRANSLUCENT POLYSTYRENE MODIFIED WITH RUBBER IMPACT-RESISTANT |
| WO1985005370A1 (en) * | 1984-05-21 | 1985-12-05 | The Dow Chemical Company | Impact-modified monovinylidene aromatic polymer injection molding resins |
| US4594391A (en) * | 1984-05-21 | 1986-06-10 | The Dow Chemical Company | Impact-modified monovinylidene aromatic polymer injection molding resins |
| DE3611704A1 (en) * | 1986-04-08 | 1987-10-22 | Basf Ag | METHOD FOR PRODUCING IMPACT RESISTANT POLY (ALKYL) STYRENE |
| DE3611705A1 (en) * | 1986-04-08 | 1987-10-22 | Basf Ag | METHOD FOR PRODUCING IMPACT RESISTANT POLY (ALKYL) STYRENE |
| US4839418A (en) * | 1988-01-05 | 1989-06-13 | Basf Aktiengesellschaft | Thermoplastic molding materials and their preparation |
| JPH0714990B2 (en) * | 1990-03-02 | 1995-02-22 | 新日鐵化学株式会社 | Method for producing rubber-modified styrenic resin |
| DE4030352A1 (en) * | 1990-09-26 | 1992-04-02 | Basf Ag | METHOD FOR PRODUCING ABS MOLDS |
| JP3345921B2 (en) * | 1992-09-30 | 2002-11-18 | 日本ゼオン株式会社 | Impact resistant polystyrene resin and method for producing the same |
| DE4416861A1 (en) * | 1994-05-13 | 1995-11-16 | Basf Ag | Expandable styrene polymers |
| US5661191A (en) * | 1995-01-13 | 1997-08-26 | Mitsubishi Chemical Basf Company Limited | Expandable rubber-modified styrene resin beads, expanded beads thereof, and expanded molded articles obtained therefrom |
| US5637646A (en) * | 1995-12-14 | 1997-06-10 | Minnesota Mining And Manufacturing Company | Bulk radical polymerization using a batch reactor |
| DE19614293A1 (en) * | 1996-04-11 | 1997-10-16 | Basf Ag | Continuous process for the production of thermoplastic molding compounds |
| US5985997A (en) * | 1997-05-23 | 1999-11-16 | Chevron Chemical Company | In situ process for making a bimodal HIPS having both high gloss and high impact strength |
| US6221987B1 (en) * | 1998-04-17 | 2001-04-24 | Asahi Glass Company Ltd. | Method for producing a fluorine-containing polymer |
| SG79291A1 (en) * | 1998-11-20 | 2001-03-20 | Daicel Chem | Rubber-containing styrenic resin and process for producing the same |
| JP2001240637A (en) | 2000-02-25 | 2001-09-04 | Nippon Zeon Co Ltd | Block copolymer rubber, resin modifier, resin composition and method for producing the same resin composition |
| JP4017994B2 (en) * | 2003-02-04 | 2007-12-05 | テクノポリマー株式会社 | Laser welding molding materials and molded products |
| EP1607436B2 (en) † | 2003-03-25 | 2019-06-12 | Sekisui Plastics Co., Ltd. | Expandable resin beads of styrene-modified linear low-density polyethylene |
| US8258083B2 (en) * | 2004-12-30 | 2012-09-04 | Sun Drilling Products Corporation | Method for the fracture stimulation of a subterranean formation having a wellbore by using impact-modified thermoset polymer nanocomposite particles as proppants |
| US20070299209A1 (en) * | 2006-06-21 | 2007-12-27 | Sosa Jose M | Methods for production of high impact polystyrene |
| AR096841A1 (en) * | 2014-07-07 | 2016-02-03 | Sotro Financial Inc | SYNTHETIC NANOCOMPOSES IN THE FORM OF MICROPARTICLES, PROCESS FOR PRODUCTION, SUPPORT AGENTS AND FRACTURE FLUIDS FOR GAS EXTRACTION PROCESSES AND OIL |
| IT201600079947A1 (en) | 2016-07-29 | 2018-01-29 | Versalis Spa | Expandable polymeric composition containing ethylene-vinyl acetate copolymers |
| WO2022043548A1 (en) | 2020-08-31 | 2022-03-03 | Ineos Styrolution Group Gmbh | Sealable multilayer film of styrene polymers with improved organoleptic properties |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3243481A (en) * | 1962-01-08 | 1966-03-29 | Dow Chemical Co | Process for making graft copolymers of vinyl aromatic compounds and stereospecific rubbers |
| GB1005681A (en) * | 1962-04-04 | 1965-09-29 | Monsanto Co | Process for polymerizing a rubber-monomer solution |
| DE1595203A1 (en) * | 1963-08-14 | 1970-04-16 | Rexall Drug Chemical | Graft polymerization process |
| GB1180085A (en) * | 1966-02-08 | 1970-02-04 | Toyo Rayon Co Ltd | Transparent Thermoplastic Composition of High Impact Resistance and manufacture thereof |
| US3660535A (en) * | 1970-09-23 | 1972-05-02 | Dow Chemical Co | Process for the production of alkenyl aromatic polymers containing a reinforcing polymer therein |
| JPS5229353B2 (en) * | 1972-05-04 | 1977-08-01 | ||
| DE2342119C2 (en) * | 1972-08-23 | 1981-11-12 | General Electric Co., Schenectady, N.Y. | High impact thermoplastic composition |
| US3903202A (en) * | 1973-09-19 | 1975-09-02 | Monsanto Co | Continuous mass polymerization process for polyblends |
-
1976
- 1976-03-29 DE DE2613352A patent/DE2613352B2/en not_active Ceased
-
1977
- 1977-02-14 GR GR52777A patent/GR65690B/en unknown
- 1977-03-07 IT IT21012/77A patent/IT1081354B/en active
- 1977-03-14 CA CA273,939A patent/CA1114984A/en not_active Expired
- 1977-03-22 FR FR7708471A patent/FR2346381A1/en active Granted
- 1977-03-23 BE BE176045A patent/BE852793A/en not_active IP Right Cessation
- 1977-03-24 NL NL7703199A patent/NL7703199A/en not_active Application Discontinuation
- 1977-03-28 GB GB12880/77A patent/GB1576772A/en not_active Expired
- 1977-03-28 ES ES457263A patent/ES457263A1/en not_active Expired
- 1977-03-29 JP JP52034074A patent/JPS6057443B2/en not_active Expired
-
1979
- 1979-11-27 US US06/097,815 patent/US4282334A/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| DE2613352A1 (en) | 1977-10-06 |
| FR2346381B1 (en) | 1983-06-03 |
| FR2346381A1 (en) | 1977-10-28 |
| NL7703199A (en) | 1977-10-03 |
| ES457263A1 (en) | 1978-02-01 |
| GR65690B (en) | 1980-10-20 |
| JPS52117990A (en) | 1977-10-03 |
| IT1081354B (en) | 1985-05-21 |
| US4282334A (en) | 1981-08-04 |
| JPS6057443B2 (en) | 1985-12-14 |
| BE852793A (en) | 1977-09-23 |
| DE2613352B2 (en) | 1980-08-07 |
| GB1576772A (en) | 1980-10-15 |
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