WO2015074988A1 - Nanoporous composite material with low density comprising hollow particles - Google Patents

Abstract

A process for producing a nanoporous composite material comprising at least the following steps: a) providing a dispersion of hollow latex particles C, comprising a hard shell, b) optionally polymerizing a at least one soft shell onto the hollow latex particles C, c) optionally swelling the latex particles with a polymerizable mixture of one or more of monomers, crosslinking agents and initiators, d) coagulating the dispersion and separating the coagulate from the water phase or forming a gel, e) filling the coagulate or gel into a mold and curing the coagulate at a temperature in the range of 20 to 100°C.

Description

Nanoporous composite material with low density comprising hollow particles Description This invention concerns a nanoporous composite material comprising hollow particles, a process for producing the nanoporous composite material and also the use of the composite material.

Nanoporous composite materials are useful as catalyst supports, solid phases for

chromatography or insulating materials. They can be made in different ways, such as by reaction (WO 2006/128872), by gelation of colloidal dispersions (WO 2005/095502), by adhering aerogels (WO 2012/76489) or by linking together hollow particles by inorganic or organic binders (US 2,797,201 ). WO 2009/043191 relates to a method for producing macro-porous materials comprising the following steps: a) synthesis of narrowly dispersed cross-linked polymeric particles starting from a monomer and a cross-linker by emulsion polymerization; b) swelling of the particles with a liquid mixture comprising at least an additional charge of monomer and cross-linker and subsequent destabilisation; c) initiation of the polymerization reaction of the swollen particles to form a monolithic structure. Such monoliths can be very efficiently functionalised if after the synthesis of the polymeric particles in step a) and before the initiation of the reaction of the swollen particles in step c) the polymeric particles are chemically functionalised or prepared for subsequent functionalization of the monolithic structure. This method is known as "reactive gelation".

DE 102 33 702 A1 discloses a process for preparation of nanocellular polymer foams involving: (a) cooling of a dispersion of polymers in a sublimable dispersion agent over a maximum of 10 seconds to a temperature below the melting point of the dispersion agent to give a frozen mixture and (b) removal of the dispersion agent by freeze drying. Dispersions comprising hollow particles and binders, such as water soluble polyacrylates, are preferred. This process is economically not viable in big scale because of the extremely fast cooling rate and subsequent freeze-drying step.

WO 2012/065288 discloses the preparation of a nanoporous composite material by dispersing nanoporous particles, such as silica aerogels, in a latex of polymeric hollow particles with rigid inner shell and adhesive outer shell. The hollow latex particles are bound directly to one another to form a continuous matrix and the nanoporous particles are dispersed within the continuous matrix of hollow latex particles. This composite material comprises of 50 to 99 vol% of nanoporous silica, so handling of large volumes of solid, dust generating inorganic nanomaterial is prerequisite, which can cause environmental and safety issues.

Y. Luo and C. Ye describe in Polymer 53 (2012) 5699 the preparation of organic polymer nanofoams with low thermal conductivity and high mechanical strength by mixing hollow nanocapsules with partially etherified melamine resins and a water-based colloidal gelation process followed by evaporation of the liquid compounds and water. The nanocapsules were synthesized by interfacial reversible addition-fragmentation chain transfer (RAFT) miniemulsion polymerization. However RAFT polymerization is expensive and difficult to scale-up and control at large scale. Because of the fast gelation reaction, homogeneity of gel is difficult to control resulting in a broad pore volume distribution in the final nanofoam.

The problem addressed by this invention was therefore that of providing nanoporous composite materials with low densities, low thermal conductivity and homogeneous and narrow pore size and pore volume distribution. The nanoporous composite materials shall also be producible in a simple manner and in commercial scale without the need of organic solvents and additional inorganic or organic binders.

The invention provides a process for producing a nanoporous composite material comprising at least the following steps: a) providing a dispersion of hollow latex particles C, comprising a hard shell,

b) optionally polymerizing at least one soft shell onto the hollow latex particles C, c) optionally swelling the latex particles with a polymerizable mixture of one or more

monomers, crosslinking agents and initiators,

d) coagulating the dispersion and separating the coagulate from the water phase or forming a gel,

e) filling the coagulate or gel into a mold and curing (by post-polymerization) and drying the coagulate or gel at a temperature in the range of 20 to 100°C.

Preferred embodiments of the present invention will now be recited, while the specifically recited embodiments shall also be combinable.

Step a)

Dispersions of colloidal hollow latex particles C (or simply "hollow latexes") with core-shell structure may be obtained by emulsion polymerization as described in EP-A 1 904 544 or EP 2 143 742. Hollow latex particles are a particular variety of core/shell particles composed in dried form of an air-filled cavity surrounded by a hard shell. This construction gives them the particular property of scattering light, which is the reason for their use as a white pigment in paints, paper coatings, and cosmetics, suncreams for example.

The hollow latex particles comprise before drying an aqueous phase as core and at least one shell. The shell of the hollow latex particles comprises 90% to 99.9%, preferably 95% to 99.9% by weight of at least one nonionically ethylenically unsaturated monomer, and 0.1 % to 10%, preferably 0.1 % to 5% by weight of at least one hydrophilic monoethylenically unsaturated monomer.

The nonionically ethylenically unsaturated monomers comprehend styrene, vinyltoluene, ethylene, butadiene, vinyl acetate, vinyl chloride, vinylidene chloride, acrylonitrile, acrylamide, methacrylamide, (Ci-C2o)alkyl or (C3-C2o)alkenyl esters of acrylic or methacrylic acid, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, benzyl acrylate, benzyl methacrylate, lauryl acrylate, lauryl methacrylate, oleyl acrylate, oleyl methacrylate, palmityl acrylate, palmityl methacrylate, stearyl acrylate, stearyl methacrylate, monomers comprising hydroxyl groups, especially C1-C10 hydroxyalkyl (meth)acrylates, such as hydroxyethyl

(meth)acrylate, hydroxypropyl (meth)acrylate, glycidyl (meth)acrylate, ricinoleic acid, palmitoleic acid, oleic acid, elaidinic acid, vaccenic acid, icosenoic acid, cetoleic acid, erucic acid, nervonic acid, linoleic acid, linolenic acid, arachidonic acid, timnodonic acid, and clupanodonic acid, preferably styrene, acrylonitrile, methacrylamide, methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, and 2- ethylhexyl methacrylate.

The monoethylenically unsaturated hydrophilic monomers comprehend acrylic acid, methacrylic acid, acryloyloxypropionic acid, methacryloyloxypropionic acid, acryloyloxyacetic acid, methacryloyloxyacetic acid, crotonic acid, aconitic acid, itaconic acid, monomethyl maleate, maleic acid, monomethyl itaconate, maleic anhydride, fumaric acid, monomethyl fumarate, preferably acrylic acid, methacrylic acid, itaconic acid, itaconic anhydride, and itaconic acid monomethyl ester.

The hard shell encloses the core. The shell polymer possesses a glass transition temperature T_g (hard shell) calculated according to the Fox equation (John Wiley & Sons Ltd., Baffins Lane, Chichester, England, 1997) of between -40°C to 180°C, preferably between 55°C to 120°C.

The final average particle size of the hollow latex particles preferably is between 300 to 800 nm. Bi- or multi-modale particle size distribution may be advanteageous to minimize interstitial volume.

Preferable the hollow latex particles C comprise polymerized acrylic monomers and/or vinylaromatic monomers. Preferred monomers are methyl methacrylate, n-butyl methacrylate, allyl methacrylate, methacrylic acid, acrylonitrile and styrene. Suitable colloidal dispersions of hollow particles are commercially available, such as for example Ultra E from Dow Chemical or AQACell DS 6273 from BASF SE. Step b)

Optionally one or more further shells may be polymerized on the hollow latex particles C from the nonionically ethylenically unsaturated monomers and monoethylenically unsaturated hydrophilic monomers described under step a). The one or more further shells formed optionally in step b) also comprises polymerized acrylic monomers and/or or vinylaromatic monomers but in a ratio which results in a lower glass transition temperature T_g of the outer shell as of the hard shell of the hollow latex particle. Preferred monomers are methyl methacrylate, n-butyl methacrylate, methacrylic acid and styrene. Preferably the soft shell formed in step b) has a glass transition temperature Tg (soft shell) calculated according to the Fox equation in the range of -60°C to 50°C. Preferably the calculated glass transition temperature Tg (soft shell) is from 5°C to 50°C lower than Tg (hard shell)

Step c)

Cross-linked polymer latex particles produced by emulsion polymerization are optionally swollen by addition of a suitable mixture of monomers, crosslinking agents and initiator.

Step d)

Coagulation or formation of gel in step d) is done by suitable destabilization of the original aqueous dispersion. This destabilization step is carefully controlled e.g. by adding a specific amount of salt, changing temperature, changing pH of the aqueous phase or applying shear. The destabilization of the dispersion is performed in such a way that "controlled" aggregation of the particles is achieved. Here controlled means that the aggregation conditions are such to develop a very open structure, with clusters of primary particles as large as the vessel containing the swollen latex, thus forming a so-called physical gel. At this stage, the particles are connected to each other by weak Van der Waals forces.

Step e)

In order to achieve good mechanical strength of the final material, an additional reactive step (so called "post-polymerization") is carried out by increasing the temperature. In this way, residual monomers and residual initiator or monomers and initiator introduced during the swelling step fully react and "freeze" the porous structure of the aggregate while imparting significant mechanical strength to the final monolith.

Combined steps c) to e) are known as "reactive gelation" and preferably carried out in the way as described in WO 2009/043191. Step e) can be carried out optionally with a 10% to 50% volume reduction once the mold is filled with the coagulate or gel and/or drying. Step e) may be carried out at ambient pressure (101 ,3 KPa) or at reduced pressure (1 - 100 KPa). The post-polymerization conditions can be adjusted to minimize such volume reduction if necessary.

Beside the hollow latex particles and the polymerizable mixture of one or more of monomers, crosslinking agents and initiators, preferably further additives are added in an total amount of from 0 to 25% by volume, more preferable in the range from 1 to 10% by volume, most preferably in the range from 0.1 to 5 % by volume of the nanoporous composite material produced. Preferably nanoporous particles, inorganic particles, especially aerogel particles, especially nanoporous particles having an average pore size less than 1 μηη, are preferably not added.

Preferably the process according to the invention consists of the steps:

a) providing a dispersion of hollow latex particles C, comprising a hard shell,

b) optionally polymerizing a at least one soft shell onto the hollow latex particles C, c) swelling the latex particles with a polymerizable mixture of one or more of monomers, crosslinking agents and initiators,

d) forming a gel,

e) filling the gel into a mold and curing (post-polymerizing) the gel at a temperature in the range of 50 to 90°C. Preferably the process according to the invention consists of the steps a) to e).

In one preferred embodiment of the process according to the present invention, the inner surfaces of the mold are moisture-permeable and hydrophobic. This can be accomplished for example by superposing metal sieves and suitable polymeric foils or membranes.

The invention provides also a nanoporous composite material obtainable by the process described above.

The density of the nanoporous composite material is preferably in the range from 10 to

300 kg/m³, more preferably in the range from 20 to 250 kg/m³, specifically in the range from 50 to 200 kg/m³ and more specifically in the range from 50 to 150 kg/m³.

The nanoporous composite materials of the present invention have thermal conductivities at atmospheric pressure between 10 and 50 mW/(m K), preferably in the range from 10 to

30 mW/(m K), more preferably in the range from 12 to 25 mW/(m K) and specifically between 14 and 20 mW/(m K). A further advantage of the nanoporous composite materials according to the present invention is their homogeneous and smooth surface. The composite materials are also particularly simple to work/machine by sawing, sanding or cutting. Additives

The composite material may comprise effective amounts of further addition agents such as, for example, dyes, pigments, fillers, flame retardants, synergists for flame retardants, antistats, stabilizers, plasticizers and IR opacifiers. Preferably the total amount of additives is in the range of from 0 to 25% by volume, more preferable in the range from 1 to 10% by volume, most preferably in the range from 0.1 to 5 % by volume. Preferably the nanoporous composite does not contain nanoporous particles, inorganic particles, especially aerogel particles, especially nanoporous particles having an average pore size less than 1 μηη. To reduce the radiative contribution to thermal conductivity, the composites may comprise IR opacifiers such as, for example, metal oxides, non-metal oxides, metal powders (e.g., aluminum powder), carbon (e.g., carbon black, graphite, diamond) or organic dyes and dye pigments, which are advantageous for uses at high temperatures in particular. Particular preference is given to carbon black, titanium dioxide, iron oxides or zirconium dioxide. The aforementioned materials can be used in each case not only singly but also in combination, i.e., in the form of a mixture of two or more materials.

With regard to cracking and breaking strength, it can further be advantageous for the composite material to comprise fibers. As fiber material there may be used organic fibers such as, for example, polypropylene, polyester, nylon or melamine-formaldehyde fibers and/or inorganic fibers, for example glass, mineral and also SiC fibers and/or carbon fibers.

In order to avoid increased thermal conductivity due to the added fibers, the volume fraction of fibers should be 0.1 to 30%, preferably 1 to 10%, and the thermal conductivity of fiber material should be < 1 W/(m K), preferably below 0,5 W/(m K), more preferably below 0,1 W/(m K)

A suitable choice of fiber diameter and/or material can effectively reduce the radiative contribution to thermal conductivity and increase mechanical strength. For this, fiber diameter should preferably be in the range from 0.1 to 30 μηη. The radiative contribution to thermal conductivity can be particularly reduced when using carbon fibers or carbon-containing fibers.

Mechanical strength can further be influenced by fiber length and distribution in the composite material. Preference is given to using fibers between 0.5 and 10 cm in length. Fabrics woven from fibers can also be used for plate-shaped articles. The composite material may additionally comprise further auxiliary materials, for example

Tylose, starch, polyvinyl alcohol and/or wax emulsions. They are used in the prior art on large industrial scale in the shaping of ceramic compositions. The composite material may further comprise added substances used in its method of making and/or formed in its method of making, for example slip agents for compression molding, such as zinc stearate, or the reaction products of acidic or acid-detaching cure accelerants in the event of using resins.

Processing

When the material is used in the form of sheet bodies, for example plates or mats, it may have been laminated on at least one side with at least one covering layer in order that the properties of the surface may be improved, for example to increase the robustness, turn it into a vapor barrier or guard it against easy soiling. The covering layers can also improve the mechanical stability of the composite material molding. When covering layers are used on both faces, these covering layers can be identical or different. Useful covering layers include any materials known to a person skilled in the art. They can be aporous and hence act as vapor barrier, for example polymeric foils, preferably metal foils or metalized polymeric foils that reflect thermal radiation. But it is also possible to use porous covering layers which allow air to penetrate into the material and hence lead to superior acoustical insulation, examples being porous foils, papers, wovens or nonwovens.

Lamination may further be carried out for example, with substantial retention of the acoustical properties, using so-called "open" systems, as for example perforated plates.

The covering layers may themselves also consist of two or more layers. The covering layers can be secured with the binder with which the fibers and the aerogel particles are bonded to and between each other, but it is also possible to use some other adhesive.

The surface of the composite material can also be closed and consolidated by incorporating at least one suitable material in a surface layer. Useful materials include, for example,

thermoplastic polymers, e.g., polyethylene and polypropylene, or resins such as melamine- formaldehyde resins for example.

In a further embodiment, the composite materials of the present invention are combined with other foams, for example polyurethane and/or polystyrene foams. In this case, the composite material of the present invention can be laminated with expanded polystyrene or admixed with polystyrene or polyurethane foams, more particularly expanded polystyrene. The mixing ratio is easily adapted to the particular requirements and can be for example in a volume ratio of 10:90 to 90:10.

Because of their good mechanical and thermal insulation properties, the nanoporous composite materials of the present invention can be used in a very wide variety of fields. Examples thereof are the thermal insulation of buildings, motorcars, aircraft or trains, fuel boilers, cooling appliances, baking ovens, heating pipes, district heating lines, liquid gas containers, night storage ovens and also vacuum insulation in technical appliances of various kinds.

More particularly, the composite materials of the present invention are useful for internal insulation to achieve a low-energy standard, for external insulation, optionally combined with cementitious and inorganic adhesives, and also as part of a combination of base render, reinforcing mortar and top render, for roof insulation, and also in technical applications in refrigerators, transportation boxes, sandwich elements, pipe insulation and technical foams.

Examples

Materials used:

2,2-azo(2-methylpropionitrile) (AIBN, Fluka, purum),

divinylbenzene (DVB, Aldrich, 80% technical),

sodium chloride (VWR, 99.9%),

sodium dodecyl sulphate (SDS, Fluka, 98%),

sodium-n-alkyl-(Cio-Ci₃) benzene sulfonate (Disponil® LDBS 20, BASF SE)

alkylpolyglycolethersulfate (Disponil FES 993, 30 wt.-% in water, BASF SE)

alkylpolyalkylenoxidphosphate (20 wt.-% in water, Lutensit A-EP A, BASF SE),

styrene (Fisher Scientific, general purpose grade),

t-Butyl hydrogen peroxide (t-BHP, Aldrich),

sodium hydroxymethanesulfinate (Rongalit C, BASF trade name, Aldrich),

All chemicals have been used as supplied without further purification. Ultra-pure grade water for chromatography has been prepared by Millipore Synergy (Millipore, Billerica, MA, USA). Deionized water for synthesis has been stripped of oxygen by degassing under vacuum and subsequent saturation with nitrogen gas.

A Hitachi L-7100 pump (Hitachi, Tokyo, Japan) was used for the semi-batch latex preparation, Lambda Vit-Fit programmable syringe pump was used for continuous feeding of initiator in reaction.

Experimental methods

Determination of Glass Transition Temperature

The glass transition temperatures were determined by theoretical calculation using the Fox equation (John Wiley & Sons Ltd., Baffins Lane, Chichester, England, 1997). 1/Tg = Wa/Tga + Wb/Tgb, Where

Tga and Tgb = glass transition temperature of polymer "a" and "b"

W_a and Wb = weight fraction of polymer "a" and "b"

Measurement of Particle Size

The particle sizes were determined using a Coulter M4+ (Particle Analyzer) or by means of photon correlation spectroscopy, also known as quasielastic light scattering or dynamic light scattering (ISO 13321 standard) using an HPPS (High Performance Particle Sizer) from

Malvern, or by means of hydrodynamic fractionation using a PSDA (Particle Size Distribution Analyzer) from Polymer Labs.

Dynamic light scattering measurements were done on a Zetasizer nano ZS 3600 (Malvern Instruments, Malvern, Worcestershire, UK).

Thermogravimetric analysis was done on a HG53 Halogen Moisture Analyzer (Mettler Toledo, Greifensee, Switzerland). Pore Size distribution was made via mercury intrusion using a PoreMaster 33 (Quantachrome GmbH & Co. KG).

BET measurement was made via nitrogen absorption according to ISO 9277 using a Nova 2000e (Quantachrome GmbH & Co. KG).

Thermal conductivity measurements:

Method A: DSC-method as described in J. H. Flynn and D. M. Levin, Thermochimica Acta 126 (1988) 93-100.

Method B: thermal conductivity measurement according to DIN EN 12667 with a hot plate apparatus, metering area was 30 x 30 mm.

Example 1 : Hollow Particle Dispersion C1 Dispersion A1 (Seed)

From 123.85 g of water, 0.88 g of sodium dodecyl benzene sulfonate (Disponil LDBS 20, 20% strength), 182 g of n-butyl acrylate, 163.45 g of methyl methacrylate and 4.55 g of methacrylic acid a preemulsion was prepared. The initial charge, consisting of 1 172.5 g of water, 70 g of Disponil LDBS 20 and also 22.19 g of the pre-emulsion, was heated to a temperature of 80°C under a nitrogen atmosphere in a polymerization vessel equipped with an anchor stirrer, reflux condenser and two feed vessels and, following the addition of 67.2 g of a 2.5 wt.-% strength solution of sodium peroxodisulfate, polymerization was run for 15 minutes. Then the remainder of the preemulsion was metered in over the course of 60 minutes at 80°C. Subsequently polymerization was continued for 15 minutes and the reaction mixture then cooled to 55°C over the course of 20 minutes. For depletion of residual monomers, 3.5 g of a 10% strength solution of tert-butyl hydroperoxide and 2.19 g of a 10 wt.-% strength solution of sodium

hydroxymethylsulfonate (Rongalit C) were then added to the reaction mixture, and after stirring 1 h and cooling to 30°C the pH of the dispersion was adjusted by addition of 4.38 g of 25% strength ammonia solution. Solids content: 19.8 wt.%

Particle size (PSDA, volume median diameter): 34 nm

Dispersion B1 (swell core) The initial charge, consisting of 1958.8 g of water and 14.54 g of Dispersion A1 (Seed), was heated to a temperature of 82°C under a nitrogen atmosphere in a polymerization vessel equipped with an anchor stirrer, reflux condenser and two feed vessels and, following the addition of 26.68 g of a 7 wt.-% strength solution of sodium peroxodisulfate, polymerization was run for 2 minutes. Then a mixture from 0.62 g allylmethacrylate and 217.34 methyl methacrylate was metered in over the course of 90 minutes together with a solution from 9.34 g

alkylpolyalkylenoxidphosphate (20 % strength, Lutensit A-EP A), 9.34 g of sodium dodecyl sulfonate (Disponil LDBS 20, 15% strength) and 166 g methacrylic acid in 562 g water. 10 minutes after finishing of the addition 92.55 g of a 1.5 wt.-% strength solution of sodium peroxodisulfate was metered in together with a mixture from 62 g n-butyl methacrylate and 345,86 g methyl methacrylate and a solution from 2.49 g Disponil LDBS 20 and 8.38 g methacrylic acid in 276,89 g of water over the course of 75 minutes. Finally the feed vessel was rinsed with 33 g water and polymerization was continued for 30 minutes.

Solids content: 21 .8 wt.%

pH: 3.5.

Particle size (PSDA, volume median diameter): 186 nm

Dispersion C1 (Hollow particles): The initial charge, consisting of 261 g of water and 273.21 g of dispersion B1 , was heated to a temperature of 81 °C under a nitrogen atmosphere in a polymerization vessel equipped with an anchor stirrer, reflux condenser and two feed vessels and, following addition of 25.2 g of a 1 1 .4% strength solution of sodium peroxodisulfate. Then preemulsion 1 , consisting of 132 g of water, 13.6 g of Disponil LDBS 20, 4.08 g of methacrylic acid, 17.5 g of methyl methacrylate, 10.88 of acrylnitril. 3.4 g of allyl methacrylate and 202.84 g of styrene, was metered in together with 24.32 g of a 2.5% strength solution of sodium peroxodisulfate over the course of 120 minutes; after the end of the feed 3.36 g of 2.5% strength solution of sodium peroxodisulfate was added and the internal temperature was raised to 92°C within 40 minutes. Then 23.76 g o methylstyrene was added and the feed rinsed with 40.5 g of water and the mixture was stirred for 20 minutes. Then 32 g of a 10 wt.-% solution of ammonia was metered in the course of 5 minutes and stirred for further 5 minutes. Then preemulsion 2, consisting of 98.44 g of water, 7g of Disponil LDBS 20, 0.28 g of methacrylic acid and 78 g divinylbenzene was added within 15 minutes. Subsequently 5.64 g of a 10% strength solution of tert-butyl hydroperoxide was added and 31 g of a 3 wt.-% aqueous solution of Rongalit C was metered in over the course of 20 minutes. 30 minutes after the end of the feed 9.16 g of a 10% strength solution of tert-butyl hydroperoxide and 5.1 g of a 3 wt.-% aqueous solution of Rongalit C were metered in parallel into the reaction mixture over the course of 60 minutes.

Solids content: 29.7 wt.%

pH: 9.5

Particle size (PSDA, volume median diameter): 389

Example 2: Hollow Particle Dispersion C2:

Dispersion B2 (swell-core) with in-situ seed:

The initial charge, consisting of 526 g of water, in a polymerization vessel equipped with an anchor stirrer, a reflux condenser and two feed vessels was heated in a nitrogen atmosphere to a temperature of 82°C. After admixing a solution of 76 g of water, 1 .41 g of Disponil FES 993 (alkyl polyglycol ether sulfates (30% strength)) and 10.96 of EFKA 3031 (polysiloxane polyalkylene oxide copolymers) and waiting for the temperature of the solution to return to 82°C, pre-emulsion 1 (consisting of 15.62 g of water, 0.28 g of Disponil FES 993, 28.66 g of methyl methacrylate and 0.34 g of methacrylic acid) and 1 1 .43 g of a 10 wt% sodium peroxodisulfate solution were admixed in succession before polymerizing for 30 min during which the

temperature within the polymerization vessel was adjusted to 85°C. Thereafter, pre-emulsion 2 (consisting of 236 g of water, 18.63 g of Disponil FES 993, 250 g of methyl methacrylate and 144.31 g of methacrylic acid) was metered in at 85°C over 120 min. Finally, the feed vessel was rinsed with 10 g of water and polymerization was continued for a further 15 min.

Solids content: 33.2%

pH: 3.6

Particle size (PSDA, volume median): 130 nm Dispersion C2 (Hollow particles):

The initial charge, consisting of 429 g of water and 80.13 g of dispersion B2 in a polymerization vessel equipped with an anchor stirrer, a reflux condenser and two feed vessels was heated in a nitrogen atmosphere to a temperature of 78°C and, following admixture of 18 g of a 2.5 wt% sodium peroxodisulfate solution, incipiently polymerized for 5 min. Then pre-emulsion 1

(consisting of 30 g of water, 3 g of Disponil LDBS 20, 2.7 g of methacrylic acid, 23.8 g of methyl methacrylate and 34 g of styrene) was added over 60 min together with 36 g of a 2.5 wt% sodium peroxodisulfate solution, starting at 78°C; the internal temperature was raised to 80°C during the addition. On completion of the additions, pre-emulsion 2 (consisting of 1 18 g of water, 7 g of Disponil LDBS 20, 2 g of linseed oil fatty acids, 0.9 g of allyl methacrylate and 296.1 g of styrene) was added over 75 min together with 9 g of a 2.5 wt% sodium

peroxodisulfate solution, starting at 80°C; during the feed the internal temperature was raised to 82°C. On completion of the feeds the internal temperature was raised to 93°C and the system was stirred for 15 min before 18 g of omethylstyrene were added. After a further 40 min of stirring, the temperature was lowered to 87°C. On attaining the temperature, the system was stirred for 15 min before 228 g of a 1.7 wt% ammonia solution were added over 30 min. After a renewed 15 min of stirring, pre-emulsion 3 (consisting of 51 g of water, 1.2 g of Disponil

LDBS 20, 0.2 g of methacrylic acid and 41.8 g of divinylbenzene) was added over 30 min. Five minutes after completion of the addition 6 g of a 10 wt% aqueous solution of feri-butyl hydroperoxide were admixed together with 25 g of water, while 31 g of a 3.3 wt% aqueous Rongalit C solution were added over 60 min.

Solids content: 28.9%

pH: 10.2

Particle size (PSDA, volume median): 387 nm

Example 3: Hollow Particle Dispersion C3: Dispersion B3 (swell-core) with in-situ seed: The initial charge, consisting of 478,53 g of water, 1 .64 g of Disponil FES 993 and 13.27 of

EFKA 3031 , in a polymerization vessel equipped with an anchor stirrer, a reflux condenser and two feed vessels was heated in a nitrogen atmosphere to a temperature of 82°C. This was followed by admixing pre-emulsion 1 (consisting of 80.68 g of water, 0.27 g of Disponil FES 993, 27.88 g of methyl methacrylate and 0.33 g of methacrylic acid) and 15.88 g of a 7 wt% aqueous sodium peroxodisulfate solution and polymerization for 30 min during which the temperature within the polymerization vessel was adjusted to 85°C. This was followed by the metered addition over 120 min of pre-emulsion 2 (consisting of 485.67 g of water, 27.22 g of Disponil FES 993, 332.32 g of methyl methacrylate, 0.9 g of allyl methacrylate and 228.82 g of methacrylic acid), at 85°C. The feed line was subsequently rinsed with 450.16 g of water.

Completion of the addition was followed fifteen minutes later by the concurrent metered addition over 75 min of 133.35 g of a 1.5 wt% aqueous sodium peroxodisulfate solution, of a mixture of 89.33 g of n-butyl methacrylate and 498.33 g of methyl methacrylate, and also of a solution of 3.59 g of Disponil LDBS 20 and 12.07 g methacrylic acid in 700 g of water. Finally, the feed vessel was rinsed with 48 g of water and the system was polymerized for a further 30 min. solids content: 33.1wt.%

pH: 2.9 particle size (PSDA, volume median): 188 nm

Dispersion C3 (Hollow particles): The initial charge, consisting of 354 g of water and 180 g of dispersion B3, in a polymerization vessel equipped with an anchor stirrer, a reflux condenser and two feed vessels was heated in a nitrogen atmosphere to a temperature of 81 °C. Addition of 25.2 g of a 1.4 wt% aqueous sodium peroxodisulfate solution was followed by the metered addition over 120 min of pre- emulsion 1 , consisting of 102 g of water, 13.6 g of Disponil LDBS 20, 2 g of linseed oil fatty acids, 17.2 g of methyl methacrylate, 10.88 g of acrylonitrile, 3.4 g of allyl methacrylate and 206.92 g of styrene, together with 24.32 g of a 2.5 wt% aqueous sodium peroxodisulfate solution. On completion of the additions, 3.36 g of a 2.5 wt% aqueous sodium peroxodisulfate solution were added and the internal temperature was raised to 92°C over 40 min. Then, 23.76 g of omethylstyrene were added over 10 min. After a further 20 min of stirring 219.28 g of a 3 wt% aqueous sodium hydroxide solution were metered in over 20 min and stirred in for

5 min. This was followed by the metered addition within 15 min of pre-emulsion 2, consisting of 40.44 g of water, 7 g of Disponil LDBS 20, 0.28 g of methacrylic acid and 78 g of styrene.

Completion of the addition was followed five minutes later by the addition of 5.64 g of a 10 wt% aqueous solution of ferf-butyl hydroperoxide and the metering over 20 min of 31 g of a 3 wt% aqueous Rongalit C solution. 30 minutes after completion of the addition a further 9.16 g of a 10 wt% aqueous solution of feri-butyl hydroperoxide and 8.52 g of a 5.1 wt% aqueous Rongalit C solution were added concurrently by metered addition over 60 min. solids content: 29.5 wt.%

pH: 8.6

particle size (PSDA, volume median): 398 nm

Example 4: Hollow Particle Dispersion C4: Dispersion (swell-core) B4 with in-situ seed:

The initial charge, consisting of 521 g of water and 1 .64 g of Disponil FES 993, in a

polymerization vessel equipped with an anchor stirrer, a reflux condenser and two feed vessels was heated in a nitrogen atmosphere to a temperature of 82°C. Then pre-emulsion 1 consisting of 15.19 g of water, 0.27 g of Disponil FES 993, 27.88 g of methyl methacrylate and 0.33 g of methacrylic acid and 1 1 .43 g of a 10 wt% sodium peroxodisulfate solution was added before polymerizing for 30 min during which the temperature within the polymerization vessel was adjusted to 85°C. Thereafter pre-emulsion 2, consisting of 485.67 g of water, 27.22 g of Disponil FES 993, 334.22 g of methyl methacrylate, 9 g of allyl methacrylate and 228.82 g of methacrylic acid was added over 120 min at 85°C. Finally, the feed vessel was rinsed with 10 g of water and the system was postpolymerized for a further 15 min. Subsequently, 133.35 g of a 1.5 wt% sodium peroxodisulfate solution; a mixture of 89.33 g of n-butyl methacrylate and 489.33 g of methyl methacrylate; and also a solution of 3.59 g of Disponil LDBS 20 and 12.07 g of methacrylic acid in 700 g of water; were added concurrently over 75 min. Finally the feed vessel was rinsed with 48 g of water and the system was postpolymerized for a further 30 min.

Solids content: 33.1 %

pH: 3.7

Particle size (PSDA, volume median): 189 nm

Dispersion C4 (Hollow particles): The initial charge, consisting of 354.16 g of water and 179.94 g of dispersion B4, in a polymerization vessel equipped with an anchor stirrer, a reflux condenser and two feed vessels was heated in a nitrogen atmosphere to a temperature of 81 °C. Addition of 25.2 g of a 1.4 wt% sodium peroxodisulfate solution was followed by the metered addition over 120 min of pre- emulsion 1 , consisting of 132 g of water, 13.6 g of Disponil LDBS 20, 2 g of linseed oil fatty acids, 10.88 g of acrylonitrile, 17.2 g of methyl methacrylate, 3.4 g of allyl methacrylate and 206.9 g of styrene, together with 24.32 g of a 2.5 wt% sodium peroxodisulfate solution. On completion of the additions, 3.36 g of a 2.5 wt% sodium peroxodisulfate solution were added and the internal temperature was raised to 92°C over 40 min. Then, 23.76 g of omethylstyrene were added over 10 min and the feed line rinsed with 40.5 g of water. After a further 20 min of stirring 32 g of a 10 wt% ammonia solution were metered in over 5 min and stirred in for 5 min. This was followed by the metered addition within 15 min of pre-emulsion 2, consisting of 98.44 g of water, 7 g of Disponil LDBS 20, 0.28 g of methacrylic acid and 78 g of divinylbenzene. Five minutes on completion of the addition were followed by the addition of 5.64 g of a 10 wt% aqueous solution of ferf-butyl hydroperoxide and the metering over 20 min of 31 g of a 3 wt% aqueous Rongalit C solution. 30 minutes after completion of the addition a further 9.16 g of a 10 wt% aqueous solution of feri-butyl hydroperoxide and 8.52 g of a 5.1 wt% aqueous Rongalit C solution were added concurrently by metered addition over 60 min.

Solids content: 29.8%

pH: 9.5

Particle size (PSDA, volume median): 398 nm

Example 5: Hollow Particle Dispersion C5: Seed dispersion A2:

A pre-emulsion was prepared from 123.85 g of water, 0.35 g of Disponil FES 993, 182 g of n- butyl acrylate, 163.45 g of methyl methacrylate and 4.55 g of methacrylic acid. The initial charge, consisting of 1 190.9 g of water, 24.97 g of Disponil FES 993 and also 22.19 g of the pre-emulsion, in a polymerization vessel equipped with an anchor stirrer, a reflux condenser and two feed vessels was heated in a nitrogen atmosphere to a temperature of 80°C and incipiently polymerized for 15 min by addition of 67.2 g of a 2.5 wt% sodium peroxodisulfate solution. Thereafter, the rest of the pre-emulsion was metered in at 80°C over 60 min. This was followed by further polymerization for 15 min and cooling down to 55°C over 20 min. To deplete the residual monomers, 3.5 g of a 10 wt% aqueous feri-butyl hydroperoxide solution and also 2.19 g of a 10 wt% aqueous Rongalit C solution were then added to the reaction mixture, which was stirred for one hour and then cooled down to 30°C, at which point 4.38 g of 25 wt% aqueous ammonia solution were added to adjust the pH of the dispersion.

Solids content: 19.9%

Particle size (PSDA, volume median): 50 nm Dispersion B5 (swell-core)

The initial charge, consisting of 1822.6 g of water and 169 g of seed dispersion A2, in a polymerization vessel equipped with an anchor stirrer, reflux condenser and two feed vessels was heated in a nitrogen atmosphere to a temperature of 82°C. Two minutes after addition of 26.68 g of a 7 wt% sodium peroxodisulfate solution, a mixture of 0.62 g of allyl methacrylate and 217.34 g of methyl methacrylate and a solution of 9.34 g of Lutensit A-EP A, 9.34 g of Disponil LDBS 20 and 166 g of methacrylic acid in 562 g of water were added concurrently over 90 min. Ten minutes after completion of the addition, 92.55 g of a 1.5 wt% sodium peroxodisulfate solution, a mixture of 62 g of n-butyl methacrylate and 345.86 g of methyl methacrylate and also a solution of 2.49 g of Disponil LDBS 20 and 8.38 g of methacrylic acid in 276.89 g of water were added concurrently over 75 min. Finally, the feed vessel was rinsed with 33 g of water and polymerization was continued for a further 30 min.

Solids content: 21 .9%

pH: 3.5

Particle size (PSDA, volume median): 190 nm Dispersion C5 (Hollow particles):

The initial charge, consisting of 261 g of water and 273.21 g of dispersion B5, in a

polymerization vessel equipped with an anchor stirrer, a reflux condenser and two feed vessels was heated in a nitrogen atmosphere to a temperature of 81 °C. Addition of 25.2 g of a 1.4 wt% sodium peroxodisulfate solution was followed by the metered addition over 120 min of pre- emulsion 1 , consisting of 132 g of water, 13.6 g of Disponil LDBS 20, 4.08 g of methacrylic acid, 17.2 g of methyl methacrylate, 10.88 g of acrylonitrile, 3.4 g of allyl methacrylate and 202.84 g of styrene, together with 24.32 g of a 2.5 wt% sodium peroxodisulfate solution. On completion of the additions, 3.36 g of a 2.5 wt% sodium peroxodisulfate solution were added and the internal temperature was raised to 92°C over 40 min. Then, 23.76 g of omethylstyrene were added over 10 min and the feed rinsed with 40.5 g of water. After a further 20 min of stirring 32 g of a 10 wt% ammonia solution were metered in over 5 min and stirred in for 5 min. This was followed by the metered addition within 15 min of pre-emulsion 2, consisting of 98.44 g of water, 7 g of Disponil LDBS 20, 0.28 g of methacrylic acid and 78 g of divinylbenzene. Completion of the addition was followed five minutes later by the addition of 5.64 g of a 10 wt% aqueous solution of fert-butyl hydroperoxide and the metering over 20 min of 31 g of a 3 wt% aqueous Rongalit C solution. 30 minutes after completion of the addition a further 9.16 g of a 10 wt% aqueous solution of feri-butyl hydroperoxide and 8.52 g of a 5.1 wt% aqueous Rongalit C solution were added concurrently by metered addition over 60 min.

Solids content: 29.7%

pH: 9.5

Particle size (PSDA, volume median): 394 nm Example 6: Dispersion D1 , soft shell formation on hollow particle dispersions C1 :

A soft shell was formed on the hollow particles C1 , where the hollow particles were used as seed latex. The shell of thickness of around 20 nm was formed around the hollow particles using 1wt% cross-linking reagent (DVB). This step was carried out in a semi-batch condition in order to avoid inhomogeneity during shell formation as the monomers (styrene and DVB) used in shell formation have different reactivity ratios.

The reaction was carried out in three-neck round bottom flask under nitrogen atmosphere. The round bottom flask was charged initially (IC) with seed latex (30 wt %) as shown in Table 1 . The temperature of the reaction was set to 40 °C using an oil bath and the mixture was stirred at 300 rpm. Redox initiator, t-BHP was added already in the initial feed when reaction temperature was reached. In another flask, an emulsion of styrene, DVB, SDS and water was prepared and kept emulsified using stirrer. This emulsion was fed continuously (CF) at 0.15g/min to the round bottom flask when reaction temperature was reached. While feeding emulsion, another part of the initiator Rongalit C (dissolved in water) was also fed at 0.062 ml/min, separately and simultaneously using a syringe pump.

Table 1 : Recipe for the formation of soft shell on seed latex (hollow particles)

Ingredients Initial charge (IC) Continuous feed (CF)

Water 4.6 g

Styrene 4.08 g

DVB 0.04 g

SDS 0.02 g

t-BHP 0.04 g at 40 °C

Rongalit C 0.04 g dissolved in 5g water

Seed latex (C1 ) 86.4 g

Diameter Particle 389 nm

Diameter Particle 410 nm The reaction progress was monitored by using dynamic light scattering measurement. After reaction, latex was kept for post polymerization for 1 hour at 60 °C in order to avoid any residual monomer in the reaction. Final latex was with 26 wt% solid content. Example 7: Nanoporous composite material from dispersion D1

In order to prepare the monolith, above prepared latex was diluted to 13 wt % and then swollen by a mixture of monomer, crosslinking agent and initiator. For swelling, 49wt % of styrene, 49 wt % of divinyl benzene and 2 wt % of AIBN initiator were mixed. The desired amount of latex was mixed with 20 wt % of swelling solution (mixed wt % of swelling mixture was respective to the weight of polymer in soft shell).

For gelation of latex, swollen latex was mixed with right concentration and amount of the sodium chloride salt. Salt concentration which can lead to the gel formation in 20-25 minutes will be selected as right concentration. Therefore, different salt concentrations were mixed with latex in 1 :1 ratio until the desired aggregation speed was obtained. After selecting right concentration of salt (which was 0.45M NaCI in this case), a desired amount of latex was mixed with that particular concentration of salt in 1 :1 ratio under vigorous stirring using a vortex mixer. After mixing with salt, the mixture was filled immediately in 1 1 cm x 6 cm x 2 cm rectangular teflon box in order to make polymer slabs of that particular size.

The above produced gel was then post-polymerized and hardened in an oven at 70 °C for 24 hours, leading to shrinking of the gel. Obtained gel, was then washed in a water bath several times by renewing the water in water bath over a period of one day. After the washing step, gel was dried under the fume hood at room temperature and ambient pressure over a period of 14 days.

Density: 1 10 kg/m³ Pore size distribution was measured via Hg-intrusion from 50 nm to 10 μηη with an average pore size of 500 nm

A sample of 19 mm in diameter and 0.8 mm in thickness was produced and the thermal conductivity was measured with 12 mW/(m K) using the DSC-method (Method A) mentioned above.

Example 8: Nanoporous composite material from dispersion C3

The hollow particle latex C3 was filtered through a 10 μηη filter. Then 150 g of the filtered latex were mixed with 9.64 g of a Styrene/AIBN mixture (9.18 g Styrene, 0.46 g AIBN). Then 1 16 g of de-ionized water was added to the latex/monomer mixture in order to set the virtual solid content of the system to the value of 20 wt%. The mixture was left under agitation for 4 h on an orbital shaker at 200 rpm in order to perform swelling of the latex particles with the monomers for enabling the post-polymerization process afterwards.

Now 200 g of the swollen latex dispersion were charged into a 500 ml. beaker under agitation at 500 rpm using a magnetic stirrer. 200 g of an aqueous salt solution (NaCI, 0.8 M) were poured slowly into the centre of the beaker (i.e., in the middle of the originated eddy), while the agitation speed was increased from 500 to 1000 rpm throughout the pouring process. After the salt solution was poured into the latex, the mixture was transferred slowly into a mould and covered with a lid. The inside dimensions of the mould were 14 x 10 x 3 cm, made of aluminum. The inner surface was lined with a Teflon sheet and an aluminium cover lid was placed on top of the mould.

The physical gelation of the particle latex was achieved in less than 1 h after the transfer of the latex into the mould. Subsequently, the covered mould was put into an oven at T = 50°C for 15 h to promote the first stage of post-polymerization of the added styrene initiated by AIBN. In a second stage, the temperature was increased to 70°C for 1 h, in order to achieve full conversion of the styrene. Then the mould was cooled down to room temperature.

The wet monolith was transferred now from the mould into a container filled with de-ionized water. Washing of the monolith was carried out by replacing daily the washing water with fresh water for 5 days, in order to remove salt and non-gelated particles or aggregates from the monolith.

The washed wet monolith was then dried at ambient conditions under still air for 10 days and after that for 2 days in a vacuum oven at 40°C and a pressure of 1 mbar.

Density: 120 kg/m³

Pore size distribution was measured via Hg-intrusion from 40 nm to 10 μηη with an average pore size of 400 nm.

BET: 505 m²/g

A sample of 120 x 80 mm with a thickness of 17 mm in was produced and the thermal conductivity was measured with 16 mW/(m K) using the Hot-Plate-method (Method B) mentioned above.

Claims

Claims:

1 . A process for producing a nanoporous composite material comprising at least the

following steps:

a) providing a dispersion of hollow latex particles C, comprising a hard shell, b) optionally polymerizing a at least one soft shell onto the hollow latex particles C, c) optionally swelling the latex particles with a polymerizable mixture of one or more of monomers, crosslinking agents and initiators,

d) coagulating the dispersion and separating the coagulate from the water phase or forming a gel,

e) filling the coagulate or gel into a mold and curing and drying the coagulate or gel at a temperature in the range of 20 to 100°C.

2. The process according to claim 1 wherein the soft shell formed in step b) has an glass transition temperature T_g in the range of -60°C to 50°C.

3. The process according to claim 1 or 2 wherein formation of gel in step d) is controlled by adding a salt, changing temperature, changing pH of the aqueous phase or applying shear.

4. The process according to any of claims 1 to 3 wherein step e) is carried out with a 10% to 50% of volume reduction in the mold.

5. The process according to any of claims 1 to 4, wherein no nanoporous particles particles are added.

6. The process according to any of claims 1 to 5, consisting of the steps:

a) providing a dispersion of hollow latex particles C, comprising a hard shell, b) optionally polymerizing a at least one soft shell onto the hollow latex particles C, c) swelling the latex particles with a polymerizable mixture of one or more of

monomers, crosslinking agents and initiators,

d) forming a gel,

e) filling the gel into a mold and curing the gel at a temperature in the range of 50 to 90°C.

7. The process according to any of claims 1 to 6, consisting essentially of steps a) to e).

8. A nanoporous composite material obtainable by the process according to any of claims 1 to 7.

9. The nanoporous composite material according to claim 8 having a density in the range from 10 to 300 kg/m³.

10. The use of the nanoporous composite material according to claims 8 and 9 for thermal insulation.