CA2064296A1 - Monodispersed acrylic polymers in supercritical near, supercritical and subcritical fluids - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A coating composition low in volatile organic solvents compris-ing a monodispersed acrylic polymer solutions containing supercritical, near supercritical or subcritical fluids as a diluent therein. Desirably, the monodispersed acrylic polymer has a molecular weight such that it is, as such, a polymeric coating vehicle.

Description

2~429~

Monodlspersed ~c~yllc Polymers In Supercrl~cal, Near Supercrl~cal ~nd Subcrl'dcal Flulds BRIEF DESCRIPTION OF THE lNVENTION

Acrylic polymer ~olutions contai~ing supercritical, near super-critical or 6ubcritical fluit dilutant in which the acrylic polymer is of the monodisper6ed-~ype and possesses desirable coating capabilities by virtue of having a M,l or Mw of at least 2,600. Significantly improved compatibility between high performance monodispersed-type acrylic polymer~ and the supercritical, near supercritical or subcritical fluids has been found to exist resulting in le~s need for volatile organic (VOC~
solvents to provide acrylic polymer ~olu~ions having a suihble viscosity for coating applications and improved sprayed coatings.
E~AcKGRou~s2 TO Tt1 INVENTIQN

Environmental collcerns have recently stjmulated the coating industry to find ~Ivays to reduce pollution by ~olatiled organic compounds u~ed as ~o~vents in painting and fi~ hing operations. A great deal of empha~is has been placed on the development of new coating tech-nologies which dimini~h the emission of organic solvent vapors. A
number of technologies have emerged to meet most but not all of the performance and application requirements, and at the ~ame time meet emis~ion requirements and regulations. T'ney are: (a) powder coatiDgs, (b) water-borne dispersions, (c) water-borne ~olution~, (d) non-aqueous dispersions, and ~e) high solids compo~itioDs. Each technolo~y has been employed in certain application~ and each 1~ ~ound a Diche in a par-ticular industry. However, at t;lle present time, none has provided the performance and application properti2s that was hoped for initially.
.~
Powder application, for e~mple, while providing ultra-low emission of organic vapors"s o~entimea c~arac~erized by poor gloss or D,l 6b87 - 20~296 good gloss with heavy orange peel, poor definition of image ~1088, ant poor film uniformity. Pigmentation incorporation is often a problem that at times requires milling and eYtrwion of tlle polymer-pigment composite mi~ture followed by cryogenic grinding. In addition, cbang-ing colors of the coatiDgs line often requires a complete clear~ing be-cause of dust contamination of the application eguipment and finishing area Water-borne coatings caDnot be applied under conditions of high relative humidity without serious coating defects. These defects result from the fact that under conditions of high humitity, water evaporates more slowly than the organic co-solvents of the coalesciDg aid. As might be expected, in the case of aqueow dispersions, the 1088 of the organic cosolvent/coalescing aid interferes with film fonnation resulting in poor gloss, poor uniformity and pin holes. Additionally, water-borne coatins are not a~ resistant to corrosive environmenb a~ are the more conventional solvent-borne coatings.
Coatings applied from OrgaDic solvenb at high solids avoid many of the pitfalls of powder and water-borne coatings. In these solvent systems, the molecular Y,reight of the polymer is often low and reactive functionality is. necessary to crosslin~ the coating after it has been applied. In reality, there is a limit in the a'oility of this technology to meet the performance requiremenb of a commercid coating opera-tion. Present high solids systems are tifficult to aply to ~lertical surfaces without running and sagging of the coating. Often they are prone to cratering and pin-holing. If they have goot r~sctivity they have poor shelf and pot-life; if they have s~elf stability then often they cure and/or crosslinl~ slowly or require high temperature and energy to cure.
The we of supercritical fluid as a transport ~nedium for the manufilcture OI surfac~ coatings is well Icnown. Genuan patent applics-tion 28 ~3 066 describes t~e use of a ga~ in t~e supercntical state a~ the fluid medium co~taining the ~olit or liquit coating substsnce in the dissolved form. In particular, the application addresses the ~oating of porow bodies with a protectant or a react~e or nonreactive decorative finish by immersion of the porous boty in the ~uperc~itical fluit coupled D~ 87 20~2~6 , ~ , with a pre~sure drop to effect the coating. The mo~t ~ ificant porou~
bodies are porous catalysts. The applicant characterizes fi~rics as porous bodies.
&nith, U.S. 4,582,731, patented April 16, 1986, and U.S.
4,734,450, patented March 29, 1988, de~cribe forrning a supercritical solution which includes a supercritical fluid ~olvent and a di~801ved solute of a solid material and spra~nnB the solution to produce a ~nolecular spray." A ~molecular spray" is defined as a spray ~of in-dividual molecules (atoms) or very sm~ll clwters of the solute.~ The Smith patent~ are directed to producing fine films and powders. T~e films are used as surface coatings.
U. S. Patent Application Serial No. 133,068 and U.S. 4,923,720, to Lee et d., disclose a proce~s and apparatus for the liquid spray application of coatins to a sub~trate while minimizine the use of the enviromnentally undesirable organic diluents The process of the application involves forming a liquid misture comprising a coat,ing polymer and a supercritical fluid sufficient to render tlle viscosity of said misture suitable for spray application and then spraying the liquid mixture onto a substrate to form a liquid coating. T~e application and patent de~cribe the addition of at least one organic solvent to the liqmd mixture prior to spraying. Tne preferred supercritic~l fluid is ~uper-critical carbon dioYide. Ihe process employs an apparatus i~ which the components of the liquid spra~r m~ture can be bler~ded and sprayed onto an appropriate substrate. The apparatus contains multiple mean~
for wpplying at lea~t one polymeric coating compound, for supplying at least one org~uc ~olvent and for supplying supercritical carbon dioxide fluid and means for forming a liquid miYture of these components.
T~ese means are combined wit~ means for spr~ying sud liquid mi~ture onto a substrate. T~e apparatw may contain ~ean~ for heating a~y of ~0 said components and/or ~aid liquid raisture of components. IJ.S. Patent Application Seri~l No. 133,088 and the patent demon~trate tlle use of supercritical fluid, sucll as supercritical carbon dionde flnid, as diluents in ~ly viscow organic sohlent borne and/or hW v~cow no~-aqueow disper~ions coatings compo~tions to dilute t~e compositions to application visco~ity required for liquid ~pray tec~iquea Tn~y furt~er D~l b687 2~296 , 4 , temonstrate that the method i8 generally applicable to all organic solvent borne coatings ~ystems.
European Patent Application 80 112823.3, published Janualy :17, 1~90, iB tirected to a liquid coatings application procecs and ap-paratw in which supercritical fluid, ~uch as supercritical carbon tio~de fluid, are uset to retuce to application conustency viscow coatings compoutions to allow for their application as liquit sprays. The coatings compositions are spra~et by passing the composition unter pressure throug~ an orifice hlto the environment of the wbstrate.
European Patent Application 8~ 112856.3, publishet Jsnusry 17, 1990, is directet to a process ant spparstw for coati~g wbstrates by a liquid spray in which 1) supercritical fluid, such as supercritic~l carbon dioxidde fluid, i8 wed as a ~iscosity reduction diluent for coating for-mulations, 2) the mi~ture of supercritical fluid ant coating formulation 1 5 is passed unter pres~ure through an orifice înto t~e en~1ironment of the substrate to form the liguid spray, and 3) the liquid spray is electrically charged by a high electrical voltage relative to the substrate.
The above technologies unply demonstrate the applicsbility of supercritical fluids as c~rriers and ViElC08ity reducers for transporting a ~lariety of coat~g materials and effecti~ely spraying them onto a coatable ~r~ce while reducing the amount of ~olatile organic com-pounds (VOCs) that are requ;red for t~e application.
European Patent Application 90 105347.09 publi~ed Sep-tember 26, 1990, also relates to the use of super~ritical fluids to replace VOCs in spray coating compoutions. It is there indicatet t~at low molecular weight polymer component mal~e~ it s~ier to stomize in 8 spray gun. To avoid the presence of elastic component of ~1isco~ty, the EP application reco~nmends t~e use of polymers l~ving a MW/Mn le~s tllan about 4, preferably less than about 3, and most preferably less ~han ~0 about 2. Table 2 of the EP publication describes tlle u~e of acrylic thermosetting oligomers ~aving a Mn f 1,000-2,000, a Mw f 1,200-2,200, and a MW/Mn of 1.1-1.5.

D,l 66~7 2~296 , 5 , The molecular weight of a polymer controls many of its physi-cal properties, such as modulw, yield ~trength, fracture toug~ness, viscosity and solubility. As the molecular weight of a polymer i8 in-creased, most of these properties increase to a masimum and then . plateau, whereas the ~olubility of a polymer decreases a8 its molecular weight is h~creased. Since many coatings are sprayed from solutions, their molecular weights mwt be chosen to ~nce solvent com-patibility, solution nscosity and the required mechanical properties.
It is recognized that short chain acry!ic oligomers are deficient in properties reqwred of a useful commercial coating unleas the a~ylic oligomer is thermosetting by being capable of being crosslinl~edI
Oligomers of this type, containing up to about 1~ monomeric units poE~ properties distinctive firom a corresponding higher molecular weight polymer. It ifi through a cro~lin~ing reaction tha~ effective coating properties are achieved using these oligomers. Polymers ha~ing more monomer units than an oligomer pa~s through a structural pha~e that introduces significant physical and chemic~l properties t~sn would not be present in the corre~ponding oligomer.

1. The defini~on of oJigomer i~ not a fi~ed one. According to the En~clo.~ of Polyrner &icnoc ond T0chwlo~, vd ~, page 485:
~OIigomer~ are the low~ , or law-DP, members of a homclogous aenes, t~e high-~W, a~ high DP, members of which ar~ pobmera. ~ . . . ~iligomera are mole~ibrb homogeneou~ p~lymer hom~ of low mdecular weight which ehow di~erencea in their pb~ical propertie~ Emflic-e~tb clear to distinql~iah among them. Oligomers can in addition be isolated fhm 1heir mistu~ aa chemiclll entWe~ using ~lasda~l fhctionating metlloda~
The Polymer Handbook, &d Edition, poge VI-2, Aate~ -rOligomers are dsSned as the low membera ~ the pa~ymeric-homclogoua ae ies, with mole~ularweights up to about 1000 - 2000.
rknchik ~t al, ~cta Pol~mer~ ~ ~1986) Nr. S, atate: ~On the Datu~al physica~ bounda~ tween bUgomer~ Imd propsr pbbmera in t~s hydrodynsmic beha~1ior ~ macromalecule~ indi:ate ~hat the number ef r~pea~ng uni~ o~ul oligomer i8 in the ~a~ge ~10-16 units.

D~l 6b87 206~29G
, ~ , The molecular weight dwtribution of a polymer also inauences ~ y of its physical properties and is often described in terms of polydispersity (MW/Mn). In a typical free radical polymerization reac-tion, poly~ners with a heterogeneow molecular weight (polymer chains of different lengths) are producet. These systems llre termed polydis-perse, where MW/Mn typically ranges from about 2 to about 4. A~ionic polymerization reactions (generally conductet at temperatures below 0C) yield polymer chains of essentially the same length. These systems are termed monodisperse, where MW/Mn typically ranges from slightly above 1.0 to about 1.6. Such control of MW/Mn has been lcnown to permit useful ~riation in polymer phy6ical properties, such as glass transition temperature, hardness, heat distortion temperature, and melt viscosity.
A~ionic polymerization i8 recognized to allow ~ynthe6is of polymers having a predictable molecular weight average and a ve~
narrow molecular weight distributions, apprcaching the Poisson dis tribution. Morton, Anionic Polvmerization: Princi~les and Practice.
Academic Press, New York, 1983, page 9. Morton, at pages 169-174, discusses monodisperse polymers, al~d at pages 174-176, lists a substan-tial number of polymers fonned by anionic polymerization that possess narrow molecular weight distributions.
Group transfer polymerization (GTP) iB an anionic polymeriza-tion tecb~ique for preparing monodisp2erse polymers at more ~oderate temperatures, e.g, room temperature. According to Web6ter, GTP is useful for producing "polymers [ofl.. low molecular weight and llaving a . . narrow molecular weight di~tribution a!~W/Mn). At a gnren tempera-ture, MW/Mn iB primarily a function of the relative rates of i~itiation _ _ _ 2. See: WebJtcr, O. W., ~ Polymes And Proce~s For l`heir Propara~oD~, U.S. Patent 4,417,0~4, November 22, 1983.
Farr~ W. B and Soga~, D. Y., ~csss For Pre~ Li~nng Polym~, U.S. PAtent 4,414372, November 8, 1~83.

3. See footnote 2.

1 6~87 ~ 7 ~ 2~6~296 and polymerization. Rate of u~itiation, ri, depend~ on initiator and c~catalyst type and relati~e concentrations. Polymerization rate, rp, is a function of monomer reacti~1ity and c~catalyst type and concentration.
For monodisper~ity, r~/rp is equ~l to or greater than 1, tbat is, the mitiation rate is at lea4st as fast as th~ polymerization rate and all chains grow simultarleously.~
Narrow molecular weight polymers ha~re ~ignificant advantages for use in solvent based coatings. The absence of low molecular weight polymer fiactions gives cured coatings with better physical properties.
In addition, tlle absence of ~igh molecular weight fractions, as pointed out herein, allows for the preparation of high ~ohds solutions from these polymers which have lower solution ~iscosities than do ~olutions con-taining polymers of the same average molecular weight prepared by free radical polymerizstion.
THE IN~NTION

This invention is directed to monodispersed acrylic polymer solution~ containing dissoh~ed supercriticP~, near supercritical or su~
critic~l fluids that contain relatively low concentrations of VOC (volatile organic compound~) ~o}vents. The in~ention invo~es an unexpected improved compatibility between monodispersed non oligomeric ac~ylic polymers and supercritical, uear wpercritical or subcritical fluids that re~ults in les~ requirement for the use of VOCB to dissohe t~e non-oligomeric ac~ylic polymer to form a oolution ha~nng suitable viscosil y and associated properties for coating applic~tions.

.

4. Web~tcr, J~pra, i~dicdes that GTP ha~ ~he abDit;y to copdymer~e . met~acrylate and a~ylate monomers, cr combma~o~ ~ acryl~te mollomers, for ~ample, ethyl and ~orbyl acrylates, to ~la~ely monodi~rse copolymers.~

D~l 6687 206~29~
~ 8 , This invention a~certaiD6s the compatibility of monodispersed non-oligomeric and non-dimeric acrylic polymers witb ~upercritical fluid, near supercritical ~luid and ~ubcritical fluid carbon dioside.
Acrylic ther)noplastic polymers having a molecular weight witable for :use as a coating, a MW/Mn ratio of from 1 to about l.B, preferably, from about 1 to about 1.4, and most preferably, from about 1.01 to about 1.3, have been found to be esceptionally useful in solution coating formula-tions for typical solution coating applications, e.g, in spray and other coating methods, using uniquely lower VOC solvent contents. This is accompli~ed by dissolution witb. or in the polymer of a supercritical fiuid, near supercritic~l fluid or subcritical fluid, such as supercritical nuid, near supercritical fluid or subcritical fluid C02, to achieve the desired coatng viscosity. Spray application of these systems can be achieved at higher solids ~ower VOC) and reduced pressure, increasing the benefits and operational latitude othe process.
This invention relates to supercritical fluid-low VOC-containing thermoplastic ac2ylic polymeric coating solutions ill which the polymer has either a Mw or Mn greater tllan 2,500, preferably greater than about 3,000, and a MW/Mn ratio of from 1 to about 1.6, as pointed out above. bl another aspect of the invention, the thermop-lastic acrylic polymer is, as such, a polymeric coating ~ehicle. In this a~pect, the polymer is not dependent upon crosslin~ing to introduce basic coating properties. In the most preferred enibodunent of the invention, this invention relates to supercritical fluid-low VOC-containing thermoplastic acrylic polymeric coating solutions in which the polymer has either a Mw or Mn greater than 3,600, even greater than about 6,000, and a MW/Mn ratio of from a~out 1.01 to about 1.03.
.1~ the mo6t preferred er~bodiment of the invention, the monodispersed thennoplsstic polymer used in the coating formul~tion .
6. Hereina~er, the~e term~ - non-~ligomeric and non-dimeric ~ are characterized as ~thermoplaAic~ which connote~ a fundunentlil ~ange in c~aracteris~icJ bet,ween the higher pdymsr~ of the in~rention and the lower polymer~ termed dimer~ and oligomer~

D~l o~87 206~9~
, 9 , ~as either a Mw or Mw greater t~an 6,000 and as high as 100,000, or greater.
e~lEF DESCRIPTION OF THE DR~wlN~s Figures 1 and 2 ~ow tlle normalized saturation pOillt as a function of Mn and polymer composition.
Figure 3 dlow8 the relationsbip of solution vi~co~ty and Mn of a number of polymers, one of wllich is monodispersed and another t~at i8 polydispersed.
DETAILED DESCRIPTI~2N OF THE INVENTION

The term "coating ~omposition," as used herein, relatea to any coating application, whet~er decorative, permg~ent, temporary, primary, secondaTy or tertialy coating, tran~itive, and ~e lil~e. It includes paints, lacquers, enamels, ~arni~es, adllesives, release agents, lubricants, cleaning agent, agricultural coating, pha~maceutical coatings, and t~e like, to t~e extent applic~ble to tlle u~e of monodispersed thermoplastic a~ylic polymers.
The invention covers the use of transportable coating composi-tions in that the liquid coating compositioI~ of tl~e in~ention may be transported fhm one place to anotller, either in a confined cont~iner or in a piping of some sort. Transporting al~o includes t~e mo~ement of tlle coating composition from a container through tubing and fiI~ally through a spray gun to a aubst~ate on W]liC~ it proceed~ to solidify.
Table 1 llhowa relevant phyaical properties of t~vo aets of thermoplastic polymers (prepared by free radical pol~merization) to demonstrate the effect of molecul~r weight on ~olution ~cosity and ~upercritical fluid C02 ~ompatibility. The two polymer Esrstems ~re ac~ylic copolymar~ of MMA (methyl methac~ylats3 ~d BA ~-butyl acrylate) with ~n'~ ranging firom 20û0 to 12,000g/mole. The f~t ~et of polymer~ was prepared from 79% Ml~ and ~1% BA w}~ile t~e seoond D~1 6687 206~2~

~ 10~

set of poly2ners was prepared from 47% MMA and 53% BA The ex-perimental details are set forth in the corresponding enumerated e~samples below.
The ~olution ~iscosities and the C02 solubilities were deter-mined from samples which were B8% (~2) total ~olids in pentyl pro-pio~ate. The total solids and ~olvent composition were held constant.
T~e ~nscosities were detennined at room temperature wing a Broo~-field DV-I~ vi~cometer. The C02 compatibility is recorded a~ the maYi-mum weight percent C02 that is compatible with the polymer at 1600 psi and 60C., and is referred to as the normalized saturation point.
Tablo 1 Ex. Composltion Mn l~w ~w~n Vts~osity Tg(OC.J
~CPs) 1 79MMAV21BA Z125 3,722 1.75 405 23.Y
2 ~ a 3263 5,544 1.70 1213 32.8 3 ~ ~ 5404 9,419 1.74 5505 32.1 4 ~ ~ 9129 19,303 2.12 39333 4~.1 5 47MMAU53BA 2331 4339 1.86 129 -10.3 6 ~ ~ 3507 9603 ?.74 262 -7 ~ ~ 4618 14740 3.19 846 2.4 ~0 8 ~ ~ 11532 51521 4.47 3540 8~
l~Qe nscosit~ of a polymer solutio~ is lcnowll to increa~e as the molecular weight and glass tran~ition temperature (Tg) of t~e polymer increase~. Tnis behavior for t~e two seb of acr~lic polymers i~
lu~trated in Table 1. Of the two ~eb, the copoly~er ~ e higher T3 (70% MMA/21% BA) gave the most dramatic incr~e in golution vi~cosity as t;he molecular wei~ht increased.

D~l b~87 --` 2~6~29~

Figure 1 shows the normalizet osturstion point as a function of Mn and polymer composition. The copol~nero contain~g 47% MMA
and 53% BA have higher normalized oaturation points over the Mn range studied than the copolymer contsining 79% MMA and 21% BA~ It shoult be noted that as the Mn'6 of the polymers increase, their re6pec-tive normalized saturstion points trop to a rninimum at a Mn f ap-pro~imately 6000 g/mole, then they plateau.
A second polymer system was used to investigate the influence of Mn and polydispersity on C02 solubility. The composition of the polymer was 66.7% MMA, 34.8% EHNU (2-ethylhexyl methacrylste), and 8.5% MAA (methac~rlic acid). The polymer was prepared by two di~erent polymerization methots. The first method, free ratical polymenzation, gave polymers with a polydispersity ranlpng firom about 2.4 to about 3.1. The second Dlethod, group tran~fer polymerization, 1 5 gave polymers with a polydispersity of about 1.1, tllus yielding monodis-persed copolymers. Table 2 shows the effect of Mn and polydispersity on the solution properties of these polymers at ~1% total solids in pentyl propionate. Using tlle data from Table 2, the plots in Figure 2 were generated. The dah ~ow that for a given MDg the polymers with low polydispersitie~ (~1.1) have lligher normalized saturation points than those polymers with higher polydisperuties (~2.4 - 3.1). A 6.1 percent increase in the normaL~zed saturation point is obser~ed as the polydis-per~ity i~ reduced from S.07 to 1.07 for Mn of approsimately 4000. A
second comparison of the normaLi~ed saturation points as a function of Mn and polydispersity is made in Table 3 for a different ~et of po~ymers (6~.2% S4.8% EHMA). The polymers were dissolved i21 methyl PROPASOL acetate at ~6% solid~. Again t~e data ~ow that the monodispersed polymer~ have greater supercritical fluid C02 solubility than ~e polydispersed polymers.

~ 1~687 20~296 , 12, Tablo 2 Ex. Polymer Polymerlzed Mn Mw MdMW Vlscoslty Wt.X
by ~cps) CO2 9 SC.7X Free Radlcal 3164 7825 2.47 6530 35.0 Methyl Meth2crylate/
34.8X
2-Ethyl-1 0 hexyl Methacrylate/

8.5X
Methacryl-lc Acld 1 5 Terpolymer ~ " ~ " 4255 13079 3.0~ 70800 30.6 Group 2770 2980 1.07 1200 37.9 Transfer 12 " ~ ~ ~ 4056 4330 1.07 3520 36.7 13 " " " " 4800 5130 1.06 7001 35.6 14 " " ~ " 6090 6490 ~.07 10460 33.~

.

206~9g Table ~

Ex. Polymer Polymerlzed Mn M",lMn WelghtX
by C2 15 C5.2X Methyl Free Radlcal 32~3 2.45 40.7 Methacryldte/
34.8X
2-Ethylhexyl Methacrylate 1 0 Copolymers 16 ~ " Free Radical 4341 2.9t 38.8 17 " " Group Transfer 2919 1.22 42.8 18 " " Group Transfer 4244 1.23 41.5 In addition to higher ~aturation points, polymers prepared by group trsnsfer polymerization llave lower solution visco~ities thsn polymers prepared by free radical polymenz~tion due to t~e sbsence of the higher molecular weight f~actions. Figure 3 shows the ef~ect of Mn and polydispersity on solution nscosity. T'ne viuo~ities of the polymer solutions prepared by free radicd polymenzation are ~e~ersl times ~reater t~an their counte~arts prepsred by GTP. For a given Mn~ the Mw (or more correctly, the M~,) has a direct influence on the solution ~isco~ity of a polymer. Thus as My increa~e~ for a given Mn~ the solution ~iscosity of a polymer increases.
The polymers of this in~lentiOn are of t}le acryhc type, t~at is, t~ey are derived from the anionic polymeriz~tion of a monomer of t~e ~0 formula ~3~96 ~ 14 R o I U
R--CH=C-C--A
wherein A Is one or rnore o~ the followin~ groups:
~.
OR
8R~
alone or with snother suitably copolgmerizable ethylenically un-r~aturated monomer that produces a monodispersed thermoplastic polymer of the tesired molecular weight. In t~e sbove, Rl i~ hydrogen, a~yl and aryl; R2, R3 and R~ are each hydrogen or monovalent orga~lic groups, such as illustrstet below.
Monomers which are suitable ~or use in the practice of t~is invention are, in general, known compounds and include, but are not limited to, the followi~g acrylic acid, metJlacrylic scid, acrylamide, methacrylamide, methyl methacrylalte; butyl methacrylate; sorbyl ac~ylate and met}lacrylate; lauryl methaclylate; ethyl acr~late; butyl aclylate; acrylouitrile; methacrylorlitrile; ~-ethylheyl methacrylate;
2-(dimethylamino)ethyl methacrylate; 2-(dimethylamino)ethyl acrylate;
3,3-dimetho~ypropyl ac~ylate; 3-methacTyloypropyl acry~ate; 2-acetoxyethyl metllac~ylate; p-tolyl methacrylate; 2,2-dimet~ylpropyl methacTylate, 2,2-dimethylbut~l mel~acrylate, 2,2,3,3,4,4,4- hèpt~
luorobut~l acrylate; methylene malono~ ile; ethyl 2- cyanoacrylate;
N,N-timethyl acrylamide; 4-fluorophenyl acrylate; 2-met~acrylo~yethyl sc~late ant linoleate; propyl ~inyl ~tetone; et~yl 2 chloroacrylate;
glycidyl methacrylatei ~metlloypropyl methacrylate; 2-[~-propenylhxylethyl methacrylate and acr~hte; phe~yl acryiate; 3-(trimetho~5ysilyl)propyl methacrylate; allyl acrylate alld methaaylate;
mono-tri~uoroet~yl itacorlate, bi~tri~uoroetllyl itaconate, mono-trinuoroethyl ~naleate, 2,2,2-trifluoroethyl methacrylate, he~
luoroisopropyl methacrylate, penhdecafluorooctyl methacrylate, 2,2,3,3,3-pentafluoropropyl acrylate, perfluorooctyl met~ac~ylate, 1,1,2,2-tetrahydro perfluorodecyl met~acryiate, 1,1,2,2~ ydro 2~6~29 ~

, 15 peri~uoroundecyl acrylate, trihydro per~uoroheptyl acrylate, vinyl tri~uoroacet~te, vinyl heptafluorobutyrate, pentafluorostyrene, vinylidene fluoride, vinyl fluoride, c~lorotrifluoroethylene, perfluorop-ropyl vinyl ether, vinyl pivalate, nnyl 2,2-timethylbutanoate, and the . li~
Certsin of t~e monomers rnay be reactive under polymeriza-tion conditions. To the extent that they are, such as in the case of COaH and OH, tlley ~hould be chemically protected, ie. deactivated as to the functionality of the groups dua~ing the polymerization. Monomers containing such deactivated groups are useful in the preparation of polymers which, upon treatment to remove tlle protective group, have functional sites along the polymer chain. Monomers which contain sufflciently sterically l~indered amine and alcohol groups that remain inert under reaction conditions may be used directly without deactiva-1 5 tion.
The anionic polymerization ~nay be carned out using conven-tional anionic polymerization conditions in tlle art, such as character-ized byMorton, supra, Webster, supra, andFa~ham et al., supra.
When using the anionic Gl~P, initiators for t~e polymenzation resction that are usef~ include: [(1- met;hoYy - 2 - methyl - 1- pro-penyl) oxy] t~imet~lyl6ilane; 2 - (trimet~ylsilyl) isobutyronitrile; ethyl 2 -(trimethylsilyl) acetate; methyl 2 - methyl - 2 - (tributylst0~nyl) pro-panoate; 1(2 - methyl - 1 - cyclohexenyl) osy] tributDlstan~ne;
trimethylsilyl nitrite; methyl 2 methyl - 2 - (trjmethylgermany~) pro-panoate; [(4,6 ~ ydro - 2 filranyl) oy] tnmethylsilane; 1(2 - methyl - 1 - propenylidene) bis (oy)] bis[trimethyl~ e]; 1(2 - met~yl - 1- [2 -(metho~ymethoxy) etho.y] -1- propenyl) oy] trimethy3~ilane; methyl t(2 - met~yl - 1 - (t~imet~ylsilylwy) - 1- propenyl3 oxy] acetate; 1(1-(methoymethoxy) - 2 - methyl - 1- prope~yl) o~5y] trunethylsilane;
~0 trimethyl ~ ', ~ - tri~(trimethylsilyl) -1, ~, 6 - ~enzenetriacehte;
dimethyl ~, ~' - bis(trimethylsilyl) - 1,3 - benzenediacetate; [1,8 -dimethoxy - 1,b - heaudiene - 1,6 - diyl bis(o~;y)] bis ttrimethy~sila~e]; t~2 - ethyl - 1- propoxy - 1- butenyl) oy] ethyl dimethyl~ilane; ethyl 2 -(tnmethyl ~ nyl) propanoate; [(1- cyclohesenyl) o~y] trimethylstan-D~l ~687 ; 2~6~2~

~ane; [(2 - methyl 1 butenylitene) bis(osy)] bis ttrimethYlsilane]; 2 -(trimethylsilyl) propanenitrile; ethyl(trimethylgermanyl) acetate; [(1-((1- dec - 2 - enyl) oxy) 2 - methyl -1- propenyl) o y] trimethyl~ilane;
phenyl 2 - methyl - 2 - (tributylstannyl) propanoate; methyl 2 - (triethyl-s~ilyl) acetate; timethyl 2,6 - bis(trimethylgermanyl) hesanedioate; 1(2 -methyl 1- cycJoheYenyl) oxy] tr!ibutylstaI~nane; [(1- methoy - 2 -methyl 1- propenyl) oy] phenyltimethyl~ilane; and t(2 - methyl -1-[2 - (tnmethylsilo~y) ethoYy] - 1- propenyl) oxy] trimethylsilane.
Preferred initiators include Ul - methoxy - 2 - methyl - 1-propenyl) oxy] trimethylsilane; 1(2 - methyl - 1- propenylidene) bis(oxy) bis [trimethyl~ ne]; trial~ylsilyl nitrite~; and [(2 - methyl - 1- [2 -(tnmethyl~iloy) ethoy] - 1 - propenyl) oy] trimethyl~ilane.
qrimethyl~dlyl ~itrile is most preferred.
Jn accortance with art de~cribed technique~, functioDal ~;ites can be provided along the pol~ner chains, or at the end of polymer chains by providing modifiers, such a~ water, in the reaction. rnis mal~e~ the polymer suitable for crosslin~ing, c~ain extenaion, ~ain brancb~ng, or for modif~ing properties such as water aorption, W
absorption, and the lilce, t~ereby enhanci~g the already a~isting f~vorable coating properties of the mo~odisperaed thermoplastic a~3ylic polymers. In GTP, the initiator moiety fo~ one end of a polymer c~ain and as a result, the polymere; may be terminally functionalized by appropriate initiator selection and polymer treatment.
Co catalysts used in GTP include zinc iodide, bro~ide, and ~hloride, mon~ and diall~laluminum halides, dial~rlaluminum o~des, tris (di~nethylamino) sulfonium dinuorotrimethylsilicate, tris (dimethyl~mino) ~ulfonium ~yanide, tetr~phenyl arsonium cyanide, tris (dimethylamino) sulfonium azide, tetraethyl ~no~ium azide, bis (diall~ylaluminum )o~ides, boron trifluoride etherate, al~ali metPI
~0 fluorides, al~li metal ~yanide~ ali metal azides, tri~ (dimet~ylamino) sulfonium difluoro triphenyl stannate, tetr~ibuty~mmonium fluoride, tetrametllylammonium fluoride, and tetraethyl ammonium ~ide.
Preferred oo-catalyst~ include souroes of fluoride ions, e~ ally tris (dimet~ylamino) sulfo~ium difluorotrimet~yl ~icate and tetrabutyl D~l 6~87 21~fi~96 ~ 17, ammonium fluoride; tetraal~ylammonium cyanites; zinc bromide, and cinc chlor~de. Ot~er co-catalysts include the independently discovered aources of bifluonde ions, ~uch a~, for eYample, tris (dimethylamino) ~ulfonium bifluoride, tetraalkyLsmmonium bifluorides, tetrsarylphos-phonium bifluorides, bifluorides of tlle allcali met~ls, especially potas-uum, and ammonium bi~uoride.
Anionic polymenzation, including GTP, may be carried out at about - 100C. to about 150C., preferably 0C. to ~O~C., most preferab-ly at ambient temperature. A sohrent is desirable but not essential to t~e reaction. The monomer~ are typically liquids and t~us sre polymerizable without a solvent, although a ~oh~ent is beneficial in controlling temperature dur~g exothermic polymerization. When a sol~ent is used, the monomer may be di~solved therein at concentra-tions of at least 1 YVt. 96, prefera~ly at lea~t 10 wt. %. The initiator i employed at a concentration 8UC~ that the monomerlinitiator molar ratio i~ greater than 1, preferably greater t;han ~. Ihe co-cat~lyst i8 normally present in such an unount tl~at the molar ratio of initiator to co-catalyst is in the range 0.1 to 600, preferably 1 to 10.
Suitable so}vents are aprotic liquids in which t}~e monomer, initiator and co-catalyst are su~iciently soluble for reaction to occur;
that i~, the material~ ~re dissol~ed at t}~e concentrations employed.
Suitable solve~ts include ethyl acetate, propionitrile, toluene, ylene, bromobenzene, dimetho~yethane, diethoxyethane, diet~ylether, tet-ramethylene sulfone, N,N - dimethyl form~mide, N,N - dimethyl 2 5 acetamide, N-methyl pyrrolidone, anisole, 2 - butmy ethoxy tr~nethyl-silane, Cellosoh~e acetate, crown ethers 8UC~ 18 - crown - 6, acetonit-rile, and tetrahydrofuran.
In the polymerization process of tl~e invention, it i8 prefera'ole to c~arge tlle initiator, co-cat~lyst, and solve~t, if u~ed, to t~e ~0 polymerzation vessel before adding the monomer(s). Although it i8 preferable to cllarge all neceswy initiator, co-catalyst and ~ol~ent to the polymerization vessel before adding monomer(s), ~ubsequent polymerization rate being controlled by monomer addition, hrther 206~296 , 18, additions of co-catalyst may ~ometimeo be neceosary to ~u~tain polymerization .
The final (non-}iving) pol~nneric product obtained i~ formed by .espo6ing the ~iving" pol~nner to an active hydrogen ~ource, ~uch as moisture or an alcohol, for example, methanol. The ~liv~ polymers rema ns living for subshntial periods provided t;hey ~re protected from active hydrogen sources such as water or alcohols. Solutions of ~living polymer6 in cupercritic~l fluid C02 alone or ~vith inert oolvents, such as hydrocarbons, are especiaUy useful for quenching t~e livin~ polymers.
The monodispersed anionic polymerized t~ermoplastic polymers may be separated from t~e polymerization reaction by conven-tional means, such as by precipitation, distillation, eYtraction and the lilce procedure6, and thereafter formulated into a coating compo~ition, uung traditional methods. The coating compositions m~y contun tyes, 1 5 pigments, reinforcing ~gent, crosdin~ers, and t~e lilce.
T'ne invention contemplates tlle u~e of coalescing agenb in t~e polymer composition where t~ere is a need for solvating or plasticizing tlle polymer when it is removed from t~e composition and di~associated from t~e ~upercritical fluid or near supercritical fluid. Solvenb, such as t~ose describet above, and conventional plasticizers m4y be incor-porated into the composition of t}le invention for ~istiDg in the ap-plication of the polymer from asso~ation with the supercritical nuid, near wpercritical fluid and subcritical fluid.
The reference to superclitical fluids as ~olvents for ~igh polymeric solids compositiono means the di~solving of the supercritical fluid in the polymer. The invention is not limited to the di~solution of t~e 8upercritical fluid by the polymer or vice ver~a; the invention encompasses as well, disper~ions and suspension~ o~ the polymer w~th the supercritical fluid. Therefore, where there i~ the tendency to lump ~0 sohrency as the function of the oupercritical fluid, it io to be understood that ~upercritical nuid solvency i8 intended to mean t~e polymer cornbined with the ~upercritical fluid i~ providet as a more dilute flowable composition by virtue of the supercritical fluid, and the~efore, D,1 6~87 2~6~29~
, 19, ~lvency means tissolvir g, ~wpending or dwpersiDg of poly neric ~olids compo8ition with the supercritical f~uid 80 that tlle combined fluidity is characterizable by a lower viscouty and a more fluid cornpodtion for transport.
The ~upercritical fluid phenomenon ;B ~vell tocumentet, see wes F-62 - F 64 of the CRC Handbool~ of Chemistry and Physics, 67th Edition, 1986-1987, published by the CRC Press, Inc., Boca Raton, Florida. At high pressure6 above the critical point, the resulting super-critical fluid, or dense gas~, ~ill athin tensities approaching those of a liquid and will assume some of the properties of a liquid. These proper-ties are tependent upon the nuid composition, temperature, and pressure.
The compressibility of supercritical fluids is great just above the critical temperature where small changes in pres6ure result in large c~anges in the den3ity of the supercritical fluid. The liquid-lilce~
behavior of a supercritical fluid at ~igher pressure~ resulb in greatly enhanced solubilizing capabilitiea compared to those of the ~subcritical~
compound, with higher difflusion coefflcients and ~n extended useful temperature range compared to liquids. Compounds of higl~ molecular weight can often be di~aolved in the supercritical fluid at relatively low temperature~. An interesting phenomenon associated ~vith ~upercnticP~l fluita i8 the occurrence of a ~t;hreshold pressure~ for solubility of a high molecular weight solute. As the preuure is increaset, the solubility of t~e solute will o~en increase by rnany orters of magnitude wit~ only a 2 5 small pressure increase.
Near-supercritical liquids d80 temonstrate solubulity charac-teristics aad other pertinent properties sim~lar to tho~e of supercritical fluids. lhe 601ute ~nay be a liqlud at the supercritical temperaturea, e~en though it iB a solid at lower te~peraturea In atdition, it has been ~0 demonstrated that fluit ~odifier~ can o~en dter ~upercritic~l fluid properties significantly, even in relatively low co~centrations, greatly increasir~g solubility for some solutes.

D~l b687 , .

~. .

2~2~6 , 20, A su~critical fluid is a material at a temperature and/or pressure 80 t~at it is below its critical point. A ~ubcritical fluid may be (i) below its critical temperature while being above its critical pres~ure, or (u) belo~r its critical pressure while being above its critical tempera-ture, or (iii) below both its critical temperature and critical pressure.
Subcritical ~uids are useful in this ca~e becau~e of the law viscosity of the monodispersed acrylic polymer~ in the coating compo~ition of the invention. ID this case, the subcritical fluid is a gas at standard condi-tions of 0C. and one atmosphere pressure (~STP" conditions).
Examples of compounds which are lcnown to have utility as ~upercritical fluids are given in Table B.

D,l $~87 2~6~2~

2 1 , Table B

Bo~ing Cn~cd Cn~cd Cn~
Point Temper~turo Pr~ure Den~itY
Compound (C) (C) (~tm)(~/cm~) C2 - 78.5 U.~ 72.~0.448 1 0 NH3 - 8~.S61~2.4 112.60.235 H20 100.00874.16 218.30.316 N20 . 88.6686.6 71.70.45 Xenon -1082 16.8 57.60.118 Xrypton -1~32 -63.8 64.30.091 Me~hane -164.00- 82.1 45.8 0.2 Eth~e - B8.6382.28 48.10203 2 5 Ethylene - 103.7 ~21 49.70.218 Propan~ - 42.196.67 41.80~17 Pehta~e 86.1 196.6 S3.90 232 Methanol 64.7 240.5 78.~0~72 Et~anol 78.6 243.0 68.00.276 7 5 Isopropanol 82.~ 235.S 47.00273 Ioobutanol 108.0276.0 42.40~72 C~lorotrifluoromethane ~1~ 28.088.7 0.579 ~onofluoromethan~ -78.4 44.6 68.0 O.S
~yclohe~anol 166.65856.0 ~8.00.273 Many other supercritical co~npound~ are cited in the aforementioned CRC Handbook of ChemiE~t~y and Phy~cs, ~upra.
Due to the low cost, low tmicity and low c~itical temperature of car~on dimide, ~up0rcritical c~rbo~ xide fluid i~ preferably u~ed in D,l ~87 20~2~
, 22 , the practice of the present invention. For many of the same reasons, nitrous o~de (N20) i8 a desirable ~upercritical fluid in the practice of the present invention. However, use of any of the aforementioned supercritical fluuds and mixtures thereof are to be considered within the ~cope of the present invention.
The solvency of supercritical carbon dio~de is similar to that of a lower aliphatic hydrocarbon and, as a result, one can consider super6critical carbon dioxide as a replacement for a hydrocarbon 801-~ent. In addition to the environmental benefit of replacing hyd-rocarbon solvents with supercritical carbon dioxide, there is a safety benefit al80, becsuse carbon dio~de is nonflammable and nontoxic.
T~e thermoplastic polymer may be employed, a~ indicated above, without the use of a ~olvent other than the supercritical fluid, near supercritical fluid or subcritical fluid. The active solvent(s) other l 5 t~an the supercritical fluid suitable i~ the practice of this invention ~cludes a~y ~olvent or mixture of solvents that is ca~able of dissolving, dispersing or suspending the polymer in cor~bination wit~ the super-critical fluid. It i8 apparent that the selection of solvent will be depend-ent upon the polymer used.
In addition to the monodispersed thermoplastic polymer that L~ contained in the solids fraction, additives that are typically utilized in coatings may also be used. For example, pigments, pigment e~tenders, metallic flal~es, fillers, d~ying agent~, anti-foaming agent~, anti-skinning agent~, wetting agents, ultraviolet ab~orber~, cro~linl~ing agents (if the monodispersed thermoplastic polymer is provided with crosslinlcable functionality), and miYtures thereof, may be utilized in the precursor compo~ition of tlle present invention.

6. How~er, ~ tstement o a~ alleged ~uivalen~y a~not be ~nded acros~
the board. A~ pointet out by McHugh ct ~, Su~cr~ntic~l Fluid Ex~tion, ButtcnuorthJ (publishcrJ Boston, MA, (1986), at pageJ t56 ?, ~ fluid fluoroal~l ~thcr pol~ncr ~xhibitJ bcttcr ~olubility in JUp~ car~oon dio~idc thon in hc~anc D~l 66B7 236~2~6 , 27 , In connection with the use of the variow additives noted above, it is particularly desirable for pigments to be present in the precursor composition inasmuch a~ they have been found to a d in the diffusion of the supercritical nuid from the sprayed composition result-ing in improved atomization.
The solvent fraction of the coating composition of the present illvention includes at least one solvent in which the monodispersed t~ermoplastic pol~nner is at least partially ~oluble. While the solvents t}lat are ~uitable for use in the present invention include any solvent or mLstures of solvent that is capable of dissolving, dispers~g or suspend-ing the solids f~action when adm~ed with the supercritical fluid, as with the monodispersed thermoplastic polymer, there are preferred solvents and solvent mi~ctures w~ich are particularly desirable. Such preferred solvents posssss certain desirable characteristics which mal~e them 1 5 generally more suitable for admi2cture with a supercritical fluid followed by spraying such admisture onto a substrate material. Generally, the selection of a particular ~olvent or solvent m~ture tepends on the particular monodispersed polymeric compounds being used.
Suitable 301vents which may be utilized with tlle monodi~
persed thennospla~tic polymer include ltetone~ such as acetone, metllyl ethyl lcetone, methyl i~obutyl lcetone, mesityl o~ide, methyl amyl lcetone, cyclohe~anone and other aliphatic }etones; esters ~uch aa methyl acetate, ethyl acetate, ~yl polycarbo~ylic a~cid esters; ethers such as met~yl t-butyl ether, dibutyl ether, methyl phenyl ether and 27 other aliphatic or allyl aromatic et~ers; glycol ethers BU~l as ethoy etllanol, butoxy ethanoL ethoxy 2-propanol, propo~y ethanol, butoxy propanol a~d other glycol ethers; glycol ether e~ter~ BU~ aB butoxy ethosy acetate, ethyl 3-ethoy propionate and other glycol ether esters;
alcohols such as met~ahol, ethanol, propanol, ~propanol, butanol, iso-butanol, amyl alcohol and ot~er aliphatic alcohols; aromatic hyd-rocsrbons cuch as toluene, sylene, and ot~er aromatics or mDcture~ of aromatic ~ol~ents; aliphatic hydrocarbons BU(~ as VM&P naphtha and ~ eral spirits, and other aliphatics or m~tures of aliphati~; nitro all~anes such as 2-Ditropropane. A renew of t~e st~uctural relatior~hips 7 5 ~mportant to the choice of solvent or oolvent blend is gi~ren by Dileep et , . .

D~l 6687 ~ a ~ 6 , 24 , ~, Ind. Ene. Chem. (Product Research and Development) 24, p. 162 (198~) and Francis, A. W., ~. Phvs. Chem. 68, p. 1099 (19~4).
In general, solvent~ 8 utable for the present invention ~hould have t31e desired solveD~y characteristics as aforementioned ant also the proper balance of eYaporation rates 80 as to ensure good coating formation. In other word~, the solvent fraction should have a proper blend of fast and P,low solvents.
More opecifically, sol~ents ~laving fast evaporation rates are needed to help solubilize the solids fraction, as well as help reduce ~cosity, and to ~ub6tantially leave the admi~ed coating composition once it has been sprayed and before the stomized droplets conhct the - substrate. Correspondinely, solvents having P~OW evaporation rate~ are also needed to help solubilize t~e ~olids f~action, but these sol~ents are primarily needed to be prese~t on t~e substrste after the atomized droplets have been applied BO a8 to provide a suitably low ~ucoeity to produce enough flow-out to obtsin a uniform and continuous coating.
However, too much of the fast solvent will produce a dry coating not having enough flow-out. Conversely, too muc~ of the slow ~olvent will produce a coating hav ng ~agging and running tefects and will not readily be dried thereby hindering the early llandling of such a coated substrAte.
Based on 8 relative ~vaporation rate (RER) to a butyl acehte standard equal to 100 using ASTM Method D3599 ~t 25C. and one atmosphere pressure, t}~e solvent fraction deEirably has the following composition of fast and alow solvents a~ representsd by corresponding RE~ ~ues:

D~l 6b'd 7 2 ~ 9 6 , 25 , Wt. 9~ of l'otal Solvent Fraction RER
30 -100% ~ 60 0 70% ~0-100 0 - 40% 101 - 250 < 10% > 250 More preferably, the solvent fraction has the following com-position:
Wt. % of TQta1 Solvent F'raction ~:R
1 5 40 -100% ~ ~0 O - 60% 60 - 100 0 - 30% 101 - 250 <6% >250 T~e surface ten~ion of a solvent represents anot~er c~arac-teristic of the solvent fraction which desirably is optimized ~o as to make it particularly 8 utable for admixtwe with a wpercriti~l fluid for spray applications. Specifically, a de~irable ~o~ent has 1eBB ~urface tension. The mDre BO~ the better. Accordi3;lgly, ~ohrenb Wit}l low ~urface ten~ion properties pravide good atomizatio~ of ~he coat~ng compositiwL q~ney pro~ride a fine aerosoL A fine aerosol desirably ~0 facilitate~ the ~cape of the ~upercritical fluid from t}le sprayet admised coating composition prior to cont~ ~e ~ubstrate.
o, wlvents ~vi~ low surf~ce tension propertie~ fu ilitate t~e formation of good quali~y coatings on the ~ubstrate by ~iding diffu~ion of any re~idusl superc~tical fluit ~om t~e applied coatiDg. I~ e ~ame D-l 668~

2~2.~
, 2~ , manner, the low surface tension solvents help to suppress the formation of ~urface bubbles caused by escaping residual oupercntical fluid.
Additiorally, solvents with low ourface tensiorl properties provide fast wetting ar~d spreading characteriEtics which ~ud in the formation of a defect-free, uniform coatîng on the substrate.
Preferably, the solvent fraction has a surface tension at 25C
which is les~ tb~n 35 dynes/centimeter. More preferably, the surface tension is less t~an 30 dynQs/centuneter, for eYample, 23-28 dynes/cen-timeter Dlustrative of such ~olvents are toluene, VM&P naphtha, butyl acetate pentyl propionate, glycol ethers, methyl PROPASOL~ acetate, UCAR E~ter EEP (both manufactured by Union Carbide Chemical &
Plastics, Company, Danbury, CT), and the lilce. Low surf~ce tension may be achieve by conventional additives to the coating composition of this invention. The~e additive~ auppress the surface ten~on of the composition as a whole. Such additives include ~ ce acti~e materiaLs, commonly lcnown as surfactants, that are well l~nown to those in the ~rt as effective in either the solvent fraction or in the coating composition as a whole.
As the admised coating composition containing the mixture of polymer, solvent and supercritical iluid, near ~upercritical fluid or ~ubcritical fluid is sprayed, e~laporation of a f~st solvent contributes to overall cooling of the sprayed composition~ Inas~uch as the solubility of mo~t supercritical fluids, near supercntical fluid or subcri~ical fluid, particularly carbon dioYide, ia higher at cooler temperatures, such cooling m~nife6tly }linders the diffusion of the supercritical fluid, near supercritical fluid or subcritical fl ud from tbe sprayed compo~ition. It is desirable to have e~entislly all of the fluid e3cape from the admised coating compo6ition once it ~as been sprayed, oo that essentially none of it is left oalce tbe atomized liquid droplets contact tlle oubstrate.
In t~s connection, the tenn liquid dropleb~ ~ meant to define a droplet containing a portion of the ~olid~ fraci;ion a~ well as a portion oithe solvent fraction, in addition to any entrained super&ritical D loo87 2~ ~29~
, 27 ~

fluid, near supercritical nuid or ~ubcritic~l nuid that may ~till be pre-sent in suc~ troplet.
In order to help r~ninuze the cooling effect caused by e~rapora-tion of the fast solvent, it is desirable tllat the ~olrent fraction ha~re an overall low heat of vaporization. Prefer~ly, the ~o~ent fraction has an overall low heat of vaporization of less than 110 calories per gram of solvent fraction and more prefer~bly, le~s than about 100 calories per gr~n of solvent fraction. Desirably, the overall heat of ~aporization of the solvent fraction is in the range of from about 66 to about 95 1 0 calories/gram.
To minimize the unnecessary release of solvent~apors into the atmosphere dur~ng the spray application of the atmD~ed coating com-positions, the amount of aolvent used in the coating compositions should be less than that required to protuce a m~ture of monodis-17 persed thermoplmtic pobmer and solvs~t ha~ing a viscosity which would pe~nit its applicstion by liquid ~pray tec~niques~ In other words, t~e inclusion of the solvent frsction should be mini~zed such thst the diluent effect due to the solubilization of the ~upercritical fluid, near supercritic~l fluid or subcritical fluid in the polymer is fully utilized~
The vi~cosi~y of the coating composition dlould be low enough ~ - suc~ that there is enough solvent present to provide proper coalescence -~ upon the ~ubstrate o~ce the compositio~ spra~red while ~till being high enough to allow for a reduction in solvent u~age 80 as to ma~mize the utilization of the supercritical fluid, near supercritical fluid or ~ubcritical fluid diluent and to concomitantly facilitate good atomization and coating fonnation.
Tne ~iscosity of the monodispersed thermoplattic ac~ylic polymer coating composition ~ould ~Lso be 8UC~ thatwheII supercritical fluid, near supercritical fluid or subcritical fluid is sdde-d, it ~ possible to~0 add enough of it witbout entering the t~vo fluid plla~e regon, ~uch ~t tlle viscosity iA lowered to less than about ~00 centipoise, above the cntical temperature and pressure of t~e oupercritic~l fluid, when used, or below ~uc~ conditions wh~n near supercritical fluid or ~itic~l D,1 6U7 2~6~
, 2~ , fluid is u6ed, so aa to render the miYture ouitable for spray application.
More preferably, the admised liquid coating composition has a viscos ty that is less that about 160 centipoise and preferably has a ~cosity in the range of from about 6 to 160 centipoi~e. Most preferably, the .~iscosity of the admiYture of solids fraction, solvent fraction and super-critical fluid, near supercritical fluid or subcritical fluid is in the range off~om about 10 to about 60 centipoise.
More particularly, the liguid mondisperset thermopla~tic acrylic polymer coating composition should have a compatibility with the aupercritical fluid, near supercritical fluid or subcriticsl fluid, above the critical temperature and pressure of the supercritical fluid, or lower in the case of the near supercritical nuid or the subcritical fluid, 80 that at least 6% by weight thereof in the liquid composition. Preferably, t~e dilutancy should be at least 16% by weight of the wpercritical fluid, near supercritical fluid or subcritic~l fluid in the misture, and more preferably, about 20 to oO% or greater by weight of supercritical fluid, near ~upercritical fluid or subcntical fluid, per liter of mi~ture. Mo~t preferably, it is in the range of from sbout 2~% to about 35% byweight.
The coating cornposition containi~g the mon~dispersed polymer, after having been admised with supercritical ~uid, ne~
~upercritical fluid or subcritical fluid, i~ sprayed onto a substrate to form a liquid coating thereon containing solids fraction, a portion of the ~olvent fraction, and any re6idual gas t}lat may be left, by p~ng the admixed liquid m~ture under pressure t~rough an oAfice into t}le enviromment of the 6ubstrate to form a liquid spray.
The spray pres6ure used in the practice of the pre~ent inven-tion is a function of the coating formulation, the ~upercritical fluid, near supercritial fluid or subcritical fluid being u~ed, and the v~cosity of t~e liqt~id ~sture. T'ne minimum ~pray pre6sure is typically at or di8htly ~0 below the critical pressure of the wpercritical fluid. Generally the pressure will be below about 6000 psL Preferably, the spray pre~sure iB
above the critical pres ure of the ~upercritical fluid and below about 3000 p8L If the ~upercritical fluid i8 supercsitical carbon dioxide fl~ud, tlle preferred spray pressure is between about 1070 p~ and about 3000 D~ 87 2afi~

, 29 , psi. The most preferred ~pray pressure is between about 1200 pu and about 2600 psi.
The ~pray temperature u~ed in the practice of the present invention iB a function of the coating formulation, the superc~tical fluid, near llupercr tical fl ud or subcritical fluid being used, and their concentration in t~e liquid mixture. The minimum ~pray temperature M at or ~ightly below tbe critical temperature of the supercritical fluid.
The ma~nmum temperature is the highest temperature at which the components of the liquid miYture are not dgnificantly thermally deg-raded during the t;me that the liquid misture iB at that temperature~
If the supercritical fluid is Bupercritical csrbon dioside fluid, because the supercritical fluid escaping from the spray no~zle could cool to the point of condensing solid carbon dio2ide and a~y ambient water vapor present due to }~g~ humidity `n the surrounding ~ray environ-l 5 ment, the spray compoùtion is preferably beated prior to atomization.
T~e minimum ~pray temperature ~ about 31C~ T}le ma~im~n tem-perature iB determined by the thennal stability of the components in the liquid mixture. The preferred spra;y temperature ~ between 35C~and 90G The most preferred temperature iB between 45C~ and 7~C~ Generally liquid mistures with greater amount~ of ~upercritical carbon dio2~ide fl~d require higher ~pray temperatures to counteract t~e greater cooling effect~
l~pically, the spray undergoes rapid cooling while it i6 clo8e to t}le orifice, 80 the temperature drop~ rapidly to ne~r or belo~v ambient temperature~ If the spray cools below ambient temperature, elltrain-ment of a~ibient air into t~e spray warm~ the ~pray to a~bient or near ambient temperature be~ore the s~ray reaches t~e substrate~ T'ni~ rapid cooling iB beneficial, because les~ active ~olvent(s~ evaporates in the ~pray in comparison to the amount of ~ohrent lost in conventioDal ~0 heated airless spr~rs. T'nerefore a greater proportion of the acS~e ~olvent is ret~ined in the coating formula~ion to aid leveling of the coating formulation on the sub~trate~ Conventional heated ai~less oprsys also cool to ambient temperature before reaching the ~u~te, becau~e of sol~ent evaporation and entrainment of ambient air~

D~l ~687 - 2a6A2s~
~ ~o~

T~e spray temperature may be obtained by heating the liquid mi~ture before it ent~rs the sprsy gun, by heating the ~pray gun itself, by circulating t}le heated liquid mu~ture to or through the ~pr~g gun to maint~in the ~pray temperature, or by a combination of methods.
Circulating the heated liquid misture through the spray gun is pre-ferred, to avoid heat 1088 and to r~untain the desired spray tempera-ture~ Tubing, piping, hoses, and the spray gun are preferably insulated or heat traced to prevent heat 1088.
l~ne en~ironment in which the liquid spray of the compoaition of the present invention is conducted i~ not narrowly critic~. However, the environmental pres6ure should be less than that required to maintain the supercritical fluid component of the liquid spray mixture in the supercritical state. Preferably, the present invention i8 con-ducted in air under conditions at or near atmospheric pressure. Other ga~ environments c~n also be used, such as air with reduced osygen content or ~ert gases ~uch a~ nitrogen, carbon dioside, helium, argon, xenon, or a mi~cture. O~ygen or osygen-enriched air i8 not desirable, because oy~gen enhances the flammability of organic components in the gpray.
The present process may be used to apply coatings by the application of liquid E~pray to a variety of substratea The choice of sub6trates is therefore not critical in the practice of the present inven-tion. Examples of suitable 8ubstrates include but are not limited to metal, wood, glass, plastic, paper, cloth, ceramic, rn~gor~ryl stone, ce-2 5 ment, asphalt, rubber, and composite materi~1~ The substrate rn~ be a conductor or a dielectric llhere are a broad ~ariety of 8pr~y den~ices tl~at one may use in car~nng out the inventio~ Essentially any 8pray gun ma;lrbe used, ~om conventional airless and air-a~isted airless spray device~ to electrostatic ~0 spray devices. The choice of spray device is dependent upon tlle l;ind of application in which the in~ention is used.
Airle6s spray wes a high pressure drop scross the orifice to propel the coating formulation through the orifice a~ lligh velociql.

D,l Sb87 206~29~
, ~,, Upon exiting the orifSce, the high-velocity liquid breal~s up ~to droplets and disperses into the air to form a liquid spray. Sufficient momentum remains af~er atomization to carry tbe droplets to the l~ubstrate. The Bpray tip iB contoured to modify the shape of the liquid spray, which is usually a round or elliptical cone or a flat fan. Turbulence promoters are sometimes inserted into the Bp~ noszle to aid atomization. Spray pressure~ typically range from 700 to 5000 psi. The pressure reqmred increa~e~ ~nth fluid viscQsity.
Air~sisted airless spray combines feature~ of air spray and airless ~pray. It wes both compressed air and high pressure drop acros6 the orifice to atomize the coating formulation and to shape the liquid spray, typically under milder conditions than each type of atomization is generated by itself. Generally the cQmpressed air pressure and the air flow rate are lower than for air ~pray. Generally tbe liquid pres6ure drop iB lower than for airless spray, but higher than for air spray. Liquid 8ptay pressures typically range from aoo to 800 p6i. The pressure required increa~e~ with fluid ~cosity.
The pre~ent invention may utilize compre6sed gas to assist formation of the liquid spray and/or to modify the s}lape of the liquid spray that comes from the orifice. The as6ist gas is typica11y compressed air at pre~sures from 6 to 80 p~i, with low pressures of 6 to 20 psi pre-ferred, but may also be air ~vith reduced osygen content or inert gases such as compressed nitrogen, carbon dioside, helium argon, or Yenon, or a misture of them. Compres~ed osygen or oxygen enriched air, as noted abo~e, is not desirable becauee oygen enhances the f~ammability of the orgaruc components in the spray. The a~sist ga~ is directed into the liquid spray as one or more big~ elo~ty jets of gas, preferably arranged symmetrically on each dde of the liquid spray to balanc~ each other.
Tne assist gas jets will preferably come frGm eas orifices built into the ~0 spray tip ant/or nozzle. The assist gas may also issue from an opening in the epray tip or nozzle that i~ a concentric aunular ring that ~a around and centered on the liquid orifice, to produce a hollow-cone ~ligh-velocity jet of gas that converges on the liquid ~r4y, but tlli~ ~eates a larger flow of assist gas that is not as desirable. The concentric annular ring may be divided into segment~, to reduce gas flow rate, and it may be D,l ~687 2~6~2~
, ~2, elliptical instead of circular, to shape the spray. Preferably the nOw rate ant pressure of the a~sist Bas are lower than those wed in air ~pray.
The a~ist gas may be heated to counteract the cooling effect of the supercritical fluid diluent in the liquid spray.
Airle~s spray and air-asusted airless ~pray can also be used with the ]iquid coating formulation heated or with the air heated or ~vith both heated. Heating reduces the nscoQty of the liquid coating formulation and aids atomization.
The material of construction of the orifice is not cr tical in the practice of the present invention, provided the material possesses necessary mechanical strength for the high spray pressure wed, has sufficient abra~ion resistance to reQst wear from fluid flow, a~d is inert to chemicals with which it comes into conhct. Any of the materials used in the construction of airless spray tips, such as boron carbide, titanium carbide, ceramic, stainless steel or brass, is suitable, with tungsten carbide generally being preferred.
Suitable orifice sizes generally range from about .004-inch to about .072-inch diameter. Because the orifices are generally not cir-cular, the diameters referred to are equivalent to a circular diameter.
The proper selection is determined by the orifice size that will supply the desired amount of coating and accomplish proper atomization for it.
Generally smaller orifices are de~red at lower nscosity and larger orifices are desired at higher n~coùty. Smailer orifices givs finer - atomization but lower nutput. Larger orifices give higher output but poorer atomization. Finer atomization i8 preferred in the practice of the pre~ent invention. Therefore small orifice aize~ from about .004-inch to about .026-inch diameter are preferred. Orifice sizes from about .Oû7-inch to about .Ol~inch diameter are Jnost preferred.
The de~ of t~e spray tip that contains the spray orifice and ~0 of the spray nozzle that contains tbe sprsy tip are not cri~ccl to the practice of the present invention. The spray tips ant ~pray no~le~
should be es~enti~lly free of protubera ces near the orifice t~at could/would ~terfere with the spray.

D~l 6~87 2~6~9~

The shape of the spray ;B not critical to the practice of the present in~ention but it can be ;mportant in some applications of the invention. The spray may be in the sl~ape of a cone t;hat is circular or elliptical in cross section or the Bp~ may be in t~e shape of a flat fan, : but the spray ie not limited to t}lese shapes. Sprays tllat are flat fans or cones that are elliptical in cross section are preferred for applications requiring a broad sweeping deposition of the coating. In those cases, wide-angle fans are most preferred.
The distance from the orifice to t~e surface iB not critical.
Generally the substrate in ~vhich a broad depo~ition of the coating is ef~ected will be spr~ed from a distance of about 4 inches to about 24 inches. A tistance of 6 inches to 18 inches iB preferred. A distance of 8 inches to 14 inche~ is most preferred.
Devices and flow designs that promote turbulent or agitated flow in the liquid mixture prior to pas~ing t~e li~id mixture unter pres~ure through tlle orifice rnay also be u~ed in t}-e practice of the pre6ent invention. Such techrliques include but are ~ot limited to the use of pre-orifices, diffiusers, turbulence plates, restrictors, flow ~plit-ters/combiners, flow impingers, screens, ba~es, vanes, ~nd other inserts, device~, and flow networks that are used in eleckostatic, airless spray and air-a~usted l~irless ~pray.
~Sltering tJle liquid misture prior to ~ow through the orifice is desirable in order to remove particulates that might plug the orifice.
Tl~is caD be done u~3ing co~ventional high-pressure paint filters. A filter 2 5 may also be in~erted at or in the gun a~d a tip screen may be inserted at the spray tip to prevent orifice plug~png. The size of the flow pa~sages in the filter should be ~naller ~han tlle dze of the orifice, preferably E~ignificantly srnaller.
Electrostatic forces are commonly utiLized vtith orifice spray~
~0 euch a~ air spray, airless spMy, and air-assisted airless spray to increase the proportion of coating compo6ition that i8 deposited onto t~e ~ub-strate from t~e ~uid spray. T'ni~ is commonly referrsd to a~ increa~ing the traDsfer ef~iciency. T'nis is done by u~ing a high elec~ical voltage D~l 6687 206~29~

relati~re to the substrate to impart a negative electrical charge to the ~pray. The substrate i~ electric~lly grounded. Thi~ creates an electrical force of attraction between the fluid ~pray particles and the ~urface, llvhich causes particles that woult otherw~e mw the ~urface to be S .deposited onto it. When the electrical force causes particles to be depo~ited on t;he edge~ and baclcside of the substrate, this effect is commonly referred to as wrap around. The ~urface should be electrical-ly conduct~g or be given a conducti~g surface before being sprayed.
Tne fluid sp~ay c~n be electricdly ~harged at any lltage of the spray formation process. It can be charged by applying high electric01 voltage and electrical current 1) within the spray gun, by direct contact with electrified walls or internal electrodes before passing through the orifice; 2) as the fluid emerges from the orifice, by electrical discharge from esternal electrodes located near the orifice and close to the spray, or 3) away from the orifice, by pa~ng the iluid spray through or be-tween electrified grids or arrays of esternal electrodes before the spray reaches tlle surface.
Elactrically charging ~he fluid ~pray as it emerge~ from the orifice i~ widely used. Usually a short pointed metal wire, srhich ex-tends from the spray noz~le to beside the ~pray, is used as the electrode.
When 8 higll electrical ~oltage is applied to the electrode, electric~l current flows f~om the point of the electrode to tl~e fluid spray, which becomes charged. This method i~ u~ed for air spra~, airless ~pray, and air-assi~ted sirless spray gun~. It is used for both }land spray guns and 2 7 sutomatic spray guns. Gener~lly the electric~l ~oltage ranges from 30 to 160 l~ilovolts. Coating fonnulations that are ~ciently cnntuctive will lealc electrical charge through the fluid to the material ~upply system;
these ~ystems must be ~olated from electrical ground 80 that the sy~tem itself becomes electrified. For safety reasons, the ~oltage of hand spray guns is usually restricted to less than 70 }ilovolts and t}le equipmsnt is designed to automstically shut ~ff the ~oltage when the current esceeds a safe level. Generally for hand spray guns the u~e~l range of electric~l current is between 20 and 100 microamperes and optimum results ~re obtained ~vith coating formulations that haYe ve~y 7 5 low electric~l conductivity, that is, very high electrical resistance.

D,l ~b~7 2~6~29~
, ~5, Method~ of electroshSic charging are known to those who are dcilled in the arS of convenSional electrostaSic ~praying. Supercritical carbon tio~cide fluid surpri~ingly has been found to be an insulating solvent wiSh good electrical properSies for electrostaSic spraying. The fluid sprays give good electroshtic wrap around the substrate. This ~hows that the particles are ~hly charged and retain ~he electric charge.
Hunud air can cause electrostatic sprays to lose their electrical charge more qui~lcly than dry a~r, hence the elecSrostatic atSraction to the substrate and wrap around is less effective. The supercritical carbon dioside fluid diluent is beneficial for spraying in a humid environment, because t~e carbon dioxide as it vents *om the spray tends to displace the humid air surrounding the spray. This helps the spray to retain its electric charge longer. When compres3ed air iB used to assist electros-tatic atomization, dry air i~ favored over humid air.
:' For electrosSaSic spraying, the subsSrate is preferably an electrical conductor such as mehl. But sub~trates that are not conduc-- tors or semiconductors can also be sprayed. Preferably they are pre-treated to create an electrical~y conducting surface. For instance, the substrate can be immersed in a special solution ~o impart conductivity to the surface.
Tne method of generating the high electrical voltage and electrical current is not critical to the practice of the current invention.
High ~roltage electrical power supplies can be used in the same way as in conventional electroshtic spraying. The power supply should have ~tandart ~afety features that prevent current or voltage ~urges. The electric~l power supply may be built into the spray gun. Ot~er c~arging methods may al~o be used.
More i~forma~on about orifice sprays such as air spray, airless ~0 ~pr~, and dr-assi~ed airless spray, about heated orifice apray~, and about electroshatic spray~g csn be obhined from the general lite~sture of the coating indus~y and from te~ical bulletins ~sued by ~pray equipment manufacturers, sucll as the following references:

f~6~1f)~
, ~h, 1. Marten~, C. R., Editor. 1974. Technolonr of Paint~arnishes and I,,acquers~ Chapter 36: Application. Robert E. Yneger Publis~ing Company, Huntington, NewYorlc.
2. Fair, James. 1983. Sprays. Pages 466 483 in Grayson, M., Editor.
5Kirlc-Othmer Encyclopedia of Chemical Technology. Third Edition.
Volume 2 1. Wiley-Interscience, New Yor}.
3. Zinc, S. C. 1979. Coating Processes. Pages 386-426 in Grayson, M., Editor. Kirk~)thmer Encyclopedia of Chemical Technology. T'nird Edition. Volume 6. Wiley-Inter~cience, NewYorlc.
104. Long, G. E. 1978 Q~srch 13). Spraying Theory and Practice.
Chemical Engineering: 73-77.
6. Tecl~ical Bulletin. Air Spray Manual. ID 10-2R. Bi~s Manuf~ctur-ing Company, Fran~lin P~rlc, Illinois.
6. Technical Bulletin. Compressed Air Spray Gun Principle~. TDl~1R-l 5 -4. Binlcs Manufacturing Company, Franl~lin Park, lllinois.
7. Technical Bulletin. Airless Spray Manual. TD11-2R. BiDlcs Manufac-turing Company, Franl~lin Parl~, Illinois.
8. Technical Bulletin. Airless Spraying. IDll-lR-2. Binlcs Manufactur-ing Company, Franklin Par~c, lllinoi~
200. Tec~nical Bulletin. Electrostatic Spra~ing. TD17-lR. Binl~ Manu-facturing Company, Frankli~ Park, Dlinois.
10. Technical Bulletin. Hot Sprayillg. TD42~ 2. Binks Manufilcturing Company, Fran~in Par~, lllinois.
11. Tec~nical bulletin on air-assisted airless spray painting ~yste~
25Kremlin, Incorporated, Addison, IlliDois.

2~6~2~
~ ~7, U. S. Patents 3,556,411; 3,647,147; 3,764,710; 4,097,000; and 4,346,849 di8clo8e ~pray nozzles and tipB for use in airless spray, includ-ing designs and methods of manufacture and methods of promoting turbulence in the atomizing fluid. U. S. Patent 3,659,787 aiscloses a spray nozzle and use of electrostatics for airless spray. U. 9. Patents 3,907,202 and 4,055,300 disclose spray no~zles and we of electrostatics for ur-assisted airless spray. None of these patenb uses supercritic~l fl~ud8 a~ diluents to epray coating formulations.
Ex~plE 1 A two riter round-bottomed flasl~ equipped with a mechanical stirrer, tllermometer, Friedrichs condenser with a nitrogen inlet, and two feed adaptors wa~ c~arged with 100.0 grams of pentyl propionate.
The solvent was heated to 160C and the temperature was contro~led with a Therm-0-Watch. A monomer miYture consisting of 237.0 grams of methyl methacIylate and ~3.0 gram8 of butyl acrylate wa~ fed via a piston pump to the f~aElc over a four hour period. Over the same time period, a mixture of a2.0 grams of tert~y-butyl peroxybenzoate dis-solved in 70.0 grams of pentyl propio~ute was fed to the flss~ ~ia a second piston pump. Af~er all ~e feeds were added, the moDomer line was flushed with 15.0 grams of pentyl propionate and the reaction mixture was allowed to coo~; out for thirty minutes at 160DC. Then 2.0 grams of tertiary-butyl peroxybenzoate dissolved in 16.0 grams of pentyl propionate wa6 fed to tJle flan~ and tlle reaction rnixture was heated for an additional two hour~ at 150C.
The resulting ac~ylic copolymer, at 59% weight ~olids, had a Brookfield ~cosity of 406 centipoises at 26C. Molecular weight determination by Gel Permeation Cbromatography (GPC) using polys-lyrene as the reference gave Mn~2125, MW-3722, and a polydisper~ity of 1.76.

D~l 66~7 2 ~ ~
~8, EX~4PIE 2 The procedure wed wa~ the l~ame as used in e~ample 1, e~cept tile monomer mi~ture con~isted of 237 grams of methyl methac~ylate . ~nd 63 grams of butyl acrylate, snd the initiator feed con~ted of 11.0 7 grams tertiary-butyl peroYybenzoate in 70.0 graim pentyl propionate.
The reaction temperature wa~ 150C. The poAt initiator consisted of 1.0 gram of tertialy-buty~ perosybenzoate in 16.0 grams of pentyl pro-pioDate. Tbe resulting copolymer, at 67% weight solids, had a Broo~field cosity of 1213 centipoises at 26C. Molecular weight determination l 0 by GPC ga~re Mn e 3263, Mw - 5544, and a polydispersity of 1.70.
EX~PIE ~

The procedure wa~ e ~ame as used example 2, except the reaction temperature wa~ 140C. ~he resulting copolymer, at 60%
weight solids, had a Brookfield ~ Co~ity of 5055 centipoi~es. Molecular weight determination by GPC gave MD - 1;404. MW e 9419~ and a polydispersity of 1.74.
EX~PIE 4 Tl~e procedure was t}~e same as esample 1, escept the initiator mi~cture con~sisted of 5.6 grams of tertia~-butyl peroxybenzoate dis 2D solved in 70.0 grams of pentyl propionate, ~nd the reaction tempera$ure ~ras 126C. The post initiator cons sted of 0.5 grams of tertiary-butyl peroxybenzoate in 15.0 grams of pentyl propionate. The re~ulting copolymer, at 60% weight solid~, ~ad a Broo~field ~iscoEiity of 39,333 centipoises at 25C. Molecular Yveight detennination by GPC gave Mn - 9129,MW ~19,303,andapolydispersityof2.12.

D,l b~87 206~%~
, ~9, E~PIE 5 The procedure was the ~ame a~ e~mple 1, except the monomer misture consisted of 141.0 gram~ of methyl methacrylate and : 169.0 grams of butyl acxylate, and the irutiator consisted of 11.0 grams tertiary-butyl peroybenzoate in 16.0 grams of pentyl propionate. The reaction temperature was 160C., and the post initiator consisted of 1.0 gram of tertiary-butyl peroybenzoate in 16.0 grams of pentyl pro-pionate. Tbe resulti~g acrylic copolymer, at 67% ~veight solids, had a Broolcfield Yiscosity of 129 centipoises at 26C. Molecular weight deter~nation by GPC gave Mn ~ 2331, MW - 4339, and a polydi~
persity of 1.86.
E~PIE ~

I'he procedure was the ~ame a~ esample 6, e~cept the reaction temperature wa~ lcept at 135C. The resulting copo.ymer, at 69%
1 5 weight solids, had a Broo~field viscosity of 262 centipoises at 25C.
Molecular weight determination by GPC ga~e Mn - 3607, Mw ~ 9603, and a polydispersity of 2.74.
Ex~pl~ 7 T'ne proceture was the same as e~nple 5, except tlle reaction temperature was lcept at 125C. The resulting copolymer, at 61%
weight ~olids, had a Broo~field ~iscosity of 840 centipo~se~ at 26C.
Moleculsr weight determination by GPC g~ve M. Y 4618, Mw - 14,740 and a polydispersity of 3.19.
EX~PIE 8 The procedure was the s~ne as e~ample 5, escept the initiator coD~isted of ~.5 grams of tertiary-butyl perosybenzoate di~o~ved in 70.
grams of pentyl propionate, and the reaction tsmperature wa~ 120C.
The post initiator consisted of 0.6-grams of tertiaIy-butyl peroxyben~

D,l b687 2~6~29~
, 40 ~

zoate in 16.0 grams of pentyl propionate. The resulting copolymer, at 69% weight ~olids, had a Broo~field ~codty of 3540 centipoi~es at 25C. Moleculsr wei~ht deten~ination by GPC gave Mn - 11632, Mw -61621 and a polydispersity of 4.47.
. E~PlE 9 T~e procedure was tl~e ~lame as e~ample 2, e~cept the monomer mu~ture consisted of 170.1 gram~ of methyl methacrylate, 104.4 grams of 2-ethylheyl met~rylate, and 26.6 grams of methac-rylic acid and the reaction temperature was 150C. The resulting terpolymer, at 61% weight solids, had a Broolcfield ~iscosity of 6530 centipoises at 26C. Molecular weight determination by GPC gave Mn ~ 3164, Mw ~ 7825, and a polydispersity of 2.47.
EX~PIE 10 The procedure was the ~me as e~ample 2, e~cept the monomer mixture consisted of 171.4 grams of methyl methacrylate, 104.4 gr~ms of 2-etllylhexyl methacrylate, and 26.5 grams of methac-rylic acid, and the reaction temperature was 130C. Tne resulting terpolymer, at 65% weight solid~, had a Broo~field nscosity of 70,800 centipoises at 25C. Molecular weight determination by GPC ga~re Mn 5 4266, Mw ~ 13,079 and a polydisper~ity of 3.07.
E~PIE 1 1 To a dried, round-~ottoDled, f~ equipped with a stirrer, nitrogen purge, and condenser were ~harged 302.4g of acetonitrile, 18.Q2g of TMSM (methyl trimethyl ~ilyl dimethyl lcetene acetal), and 0.6 mL of catalyst (O.lM solution of tri (dimethylamino)sulfur(trimethyl-dlyl)di~uoride in acetonitrile). A monomer feed composed of 174.38g (1.7417 moles) of methyl metllacrylate, 107.1g of 2~thyl~e~1 methacIylate (0.6403 mole), and 48.26g of trime~hylsikyl metl~ ylate (O. 3049 mole) was fed in the reactor at room temperature ~nthin 30 ~0 minutes, t31en an additional one mL of catalyst solutionwa~ add~ The ~ 41 ~ 2~6~

temperature rose from 24C to 30C. After 16 hours, no esot~erm was spparent, and the hydroly~is of the polymer was beg~L To the polymer solution were adted 44g of a oO% (by weight) water solution of THF, and the polymer solution heated at 60C. for two hours. The polymer vras then precipitated by slowly dropping it into stirring water (16 part~
water to 1 part polymer solution, by volume). The polymer was filter, snd ~rscuum dried overnight at 83C. The final yield of polymer was 304g, acid level, 7.7 (theoretical, 8.63%); Mn~ 2770g/mole; Mw, 2980g/mole.
1 0 EX~PIE 1 2 The procedwe was essentially the same ~8 esample 11 escept tl~at 13.98g of TMSM was used. T'ne yield of polymer was 304g, acid le~el,8.4% (t~eoreticai, 8.53%); Mn~ 4066; Mw~ 4330.
EX~PIE 1 ~

T'ne procedure was essentially t;he saIne as esample 11 eYcept that 11.12g of TMSM was used. The yield of polymer was 301g, acid level, 7.6% (theoretcial, 8.63%); Mn~ 4800; M~" 6130.
E~PIE 14 The procedure wa8 essentially the same as example 11 except that 9.32g of TMSM was wed. The yield of polymer wa~ 306g, acid level, 7.6% (theoretical, 8.63%); Mn~ 6090; Mw, 6490.
EX~PlE 1 5 The procedure ~va~ the ~ame as esample 2, e:lccept the monomer rnisture consis$ed of 196.6 grams of methyl met~acrglate and 25 104.4 grams of 2-ethyllleyl methacryla~e. Af$er completing the polymerization, the product was s$ripped of pentyl propionate by placing the mi~ture under high vacuum (~1Omm) and w~rming to 60C. An D~l 66~7 2~ 2~
, 42 , equal weight of methyl PROPASOL acetate was t~en added to replace the pentyl propionate removed. The re~ulting copolymer, at 67%
weight solids, had a Broolcfield viscosity of 2100 centipoises at 26C.
Molecular weight determination by GPC gave Mn - 3213, M~v - 7865, .and a polydi~persity of 2.45.
EX~4PIE 16 - T'ne procedure was the same as eYample 1~, escept the reac-tion temperature was 130C. The resulting copolymer, st 66% weight 801ids, had a Brool~ield viscosity of ao,ooo centipoises at 25C.
1 0 Molecul~r weight determination by GPC gave Mn ~ 434 1, MW - 12,636, and a polydisper~ity of 2.91.
EX~MPIE 1 7 To a dried, round-bottomed, fla~ilc equipped with a s~rer, nitrogen purge, and condenser were ~hsrged 210g of acetonitrile, 12.96g 1 5 of TMSM (methyl trimethyl silyl dimethyl lcetene asetal), and 0.4 mL of ca~alyst (O.L~ solution of tri(dimethylsmino) sulfur - (trmethylsilyl) difluoride in acetonitrile). A monomer ~eed composed of 136.92g (1.3676 moles) of methyl methac~late, and 73.08g of 2-ethylhe~yl met~ ylate (0.3687 mole) was fed in the r~actor at room temperature within 30 mfnutes, then an additional 0.7 mL of catalyst ~olution was added. I"ne temperature rose from 24C to 41C. After 16 hours, no eYotherm was apparent, and the hydrolysis of the polymer was begun.
T'ne polymer was precipitated by ~lowly dropping it into sti~ing water (16 parts water to 1 part polymer solution, by volume). The polymer was tl~en filter, and vacuum dried ovenught at 70C. T'ne final yield of polymer ~a~ 221g, Mn 2919g/mole; Mv~ S561g/mole.

D,l bb87 206429~
, 4~ , EX~PIE 18 rne procedure was essenti~lly the ulme lu e~mple 17 ~cept that 8.46g of TMSM wa~ used. The yield of polymer wa~ 218g, Mn1 4244;
M~v, 6178.
' .

D~ 87

Claims (18)

1. A coating composition low in volatile organic solvents which comprises a monodispersed aclylic polymer solutions containing super-critical, near supercritical or subcritical fluids as a diluent therein.

2. The coating composition of claim 1 wherein the monodis-persed acrylic polymer is a thermoplwtic that possesses coating proper-ties.

3. The coating composition of claim 2 wherein the monodis-persed thermoplastic acrylic polymer has a molecular weight suitable for use as a coating and a Mw/Mn ratio of from 1 to about 1.6.

4. The coating composition of claim 3 wherein the monodis-persed thermoplastic acrylic polymer has a molecular weight suitable for use as a coating and a Mw/Mn ratio of from 1.01 to about 1.4.

5. The coating composition of claim 4 wherein Mw/Mn ratio is from 1.05 to about 1.03.

6. The coating composition of claim 1 wherein the polymer has either a Mw or Mn greater than 2,500.

7. The coating composition of claim a wherein the polymer has either a Mw or Mn greater than 2,500.

8. The coating composition of claim 3 wherein the polymer has either a Mw or Mn greater than 2,500.

9. The coating composition of claim 4 wherein the polymer has either a Mw or Mn greater than 2,500.

10. The coating composition of claim 6 wherein the polymer has either a Mw or Mn greater than 2,500.

11. The coating composition of claims 6 wherein the polymer has either a Mw or Mn greater than 3,000.

12. The coating composition of claim 7 wherein the polymer has either a Mw or Mn greater than 3,000.

13. The coating composition of claim 8 wherein the polymer has either a Mw or Mn greater than 3,000.

14. The coating composition of claim 9 wherein the polymer has either a Mw or Mn greater than 3,000.

15. The coating composition of claim 10 wherein the polymerhas either a Mw or Mn greater than 3,000.

16. A coating composition comprising a supercritical fluid-low volatile organic compound containing thermoplastic acrylic polymeric coating solutions in which the polymer has either a Mw or Mn greater than 2,500, and a MW/Mn ratio of from 1 to about 1.5, and the thermop-lastic acrylic polymer is, as such, a polymeric coating vehicle.

17. The coating composition of claim 16 wherein the thermop-lastic aclylic polymer has either a Mw or Mn greater than 3,500, and a Mw/Mn ratio of from about 1.01 to about 1.03.

18. The coating composition of claim 17 wherein the thermop-lastic acrylic polymer has either a Mw or Mn greater than about 5,000.