WO1992017509A1

WO1992017509A1 - Precipitation polymerization process

Info

Publication number: WO1992017509A1
Application number: PCT/US1992/002286
Authority: WO
Inventors: Jenn S. Shih; Terry E. Smith
Original assignee: Isp Investments Inc.
Priority date: 1991-04-01
Filing date: 1992-03-23
Publication date: 1992-10-15
Also published as: AU1692392A

Abstract

What is provided herein is a precipitation polymerization process wherein homopolymers, copolymers and polymer mixtures with comonomers are produced in an advantageous manner, preferably as fine powders, at a high solids level, in high yield having a low residual monomer content, which may contain entrapped droplets of other materials, such as silicon compounds.

Description

PRECIPITATION POLYMERIZATION PROCESS

Many monomers and monomeric mixtures capable of forming polymeric precipitates are known as well as the preparation of their polymeric products by reacting the monomers in aqueous or organic liquid media or in a Redox system. However, these processes, as described in the prior art, have many disadvantages and objectionable side effects among which are relatively low yields of pure polymeric product and polymers which are generally colored or subject to discoloration due to the presence of residual monomer. Also, many of these prior processes produce products in the form of gels or gummy gelatinous materials which are difficult to handle and from which the polymer is not easily isolated. Although homogeneous polymerization processes have achieved low residual monomer content, the product produced, often a flammable product solution, is gummy or highly viscous and polymeric product recovery very difficult as opposed to heterogeneous systems where the product is directly recovered as a precipitate. However, substantially all of the prior heterogeneous methods have been unable to produce a product in which the objectionable and contaminating monomeric residue is reduced to less than 0.1% (1,000 ppm). Reduction to practically exclusion of the monomer, e.g. to less than 1,000 ppm, is the desired goal of research since entrained monomeric moieties, even in small quantities, noticeably degrade polymeric properties, and in some instances, may have a carcinogenic effect which is particularly objectionable when the polymer is used in cosmetic and biological formulations. Finally, many of the prior polymerizations produce low molecular weight products since they are carried out under conditions which provide a short propagation stage resulting from the formation of a highly viscous reaction mixture thus hindering agitation and tending to terminate the reaction. In the Redox system for polymerization of acrylic acid/lactam monomers, it has been found that only certain proportions of monomer and comonomer produce commercially acceptable yields and that when the lactam is present in excess, the conversion to copolymer is less than 60%.

Accordingly, in one embodiment of this invention there is provided a heterogeneous, liquid phase process which comprises contacting a solution of a polymerizably precipitatable monomer or monomeric mixture with an initiating amount of a high temperature, free radical initiator having at least a 10 hour half-life at 100°C. and polymerizing the resulting mixture at a temperature of from about 110° to about 150°C. while maintaining vigorous agitation and an oxygen-free, anhydrous atmosphere throughout the reaction to produce a particulate polymer containing less than 0.1% (1,000 ppm) lactam residual monomer and having a glass transition temperature (Tg) in excess of the temperature at which polymerization is effected.

As another feature of the invention, there is provided herein a process for making homopolymers of vinylcaprolactam in the form of fine powders at a solids level of at least about 17%, preferably 30%, and in a yield of at least 95%, preferably 98%, by precharging a reactor with a predetermined amount of a solvent which is a non-solvent for polyvinylcaprolactam at the reaction temperature effecting little or no plasticization, and is a ^c ₃~^c2₀ ^aJ-kane, preferably heptane, and a free radical polymerization initiator, and feeding vinylcaprolactam monomer into the precharged reactor at a selected rate, preferably about 0.75 to 1.5 g vinylcaprolactam/min/1000 g of heptane, which rates preclude build-up of monomer during the polymerization, and for a feed period which provides the desired level of polymer solids in the reaction product, preferably at least about 120 minutes. The polymer product may be isolated from the reaction mixture by filtration and drying, or by direct drying.

In another embodiment of the precipitation polymerization process of the invention, the polymerization is carried out in a reaction mixture of vinyl lactam such as vinyl pyrrolidone or vinyl caprolactam and acrylamide, in the presence of a polymerization initiator, e.g. a free radical initiator, in an aliphatic hydrocarbon solvent, preferably, a ₃-C₁₀ saturated, branched or unbranched, cyclic or acyclic, and preferably heptane, hexane or cyclohexane.

The precipitation polymerization process of the invention may be used for entrapping droplets of a silicon compound in an organic polymer. Such process involves precharging a reactor at between about 50 and about 80°C. with a polymerization initiator and a non-polar solvent in which the silicon compound is soluble; adding to the precharged reactor, a silicon compound under vigorous agitation and gradually introducing from about 50 to about 99 wt. %, based on silicon compound, of a polymerizably precipitatable, aliphatically unsaturated monomer at a controlled rate; continuously polymerizing the monomer component, under vigorous agitation with the silicon compound, at between about 50 and about 165°C. while maintaining a desired monomer level of not more than 10% in the reactor and recovering a solid particulate product of silicon droplets entrapped in said polymerized monomer. - A -

The precipitatable monomers useful in this invention are polar compounds whose polymers have a Tg greater than 110°C. which include individual monomers as well as monomeric mixtures whose copolymeric products possess an equally high Tg. Examples of homopolymerizable monomers included in this invention are N-vinylpyrrolidone, alkyl substituted N-vinylpyrrolidones, N-vinyl caprolactam, alkyl substituted N-vinyl caprolactams, acrylic acid, methacrylic acid, acrylamide, methacrylamide, etc. Copolymers within this group are also suitable candidates for the present high temperature polymerization reaction. Additionally, nonpolar monomers, when used in an amount less than 30% of the total monomer content, can be included to form a monomeric mixture whose copolymers have certain desirable properties. These monomers, preferably employed in an amount not more than about 20%, include styrene, tetrafluoroethylene, isoprene, ethylene, isopropylene, isobutylene, acrylonitrile, C-^ to C₄ alkyl acrylate or methacrylate, vinyl chloride, vinyl acetate, N,N-dimethylamino C-^ to c₄ alkyl acrylates or ethacrylates and the like. Suitable comonomers may also include cross-linking agents such as the divinyl ether of diethylene glycol, N,N-divinyl-imidazolidone, pentaerythritol triallyl ether, triallyl-1,3,5-triazine-2,4,6-(1H,3H,5H) trione, ethylene glycol diacrylate, 2,4,6-triallyloxy-l,3,5-triazine, 1,7-octadiene, 1,9-decadiene, divinyl benzene, ethylene bis(acrylamide) , ethylene bis(methacrylamide) and the like.

The monomer or monomeric mixture may be predissolved in from about 50 to about 90 wt. %, preferably from about 70 to about 85 wt. % of a nonpolar solvent for introduction into the reactor. Suitable solvents include cyclohexane, heptane, benzene, toluene, xylene, ethyl benzene, and linear, branched or cylic alkanes having from 2 to 20 carbon atoms. High temperature free radical initiators for use herein having at least a 10 hour half-life at 100°C. are used for the reaction at about 110°-150°C. and include those having a boiling point above 110°C. such as 2,5-dimethyl-2,5-di(t-butylperoxy) hexane, di-t-butyl peroxide, dicumyl peroxide, t-butylcumyl peroxide, t-butylperoxy maleic acid, t-butyl hydroperoxide, 2,2-di(t-butylperoxy) butane, ethyl-3,3-di(t-butylperoxy) butyrate, t-butylperoxy acetate, t-butylperoxy benzoate, n-butyl-4,4-bis(t-butylperoxy) valerate, 2,5-dimethyl-2,5-di(benzooylperoxy) hexane, di-t-butyl-diperoxy phthalate, t-amylperoxy benzoate, 2,5-dimethyl-2,5-bis(benzoylperoxy) hexane, 2,5-dimethyl-2,5-di(t-butylperoxy) hexyne-3, 00-t-butyl-O-(2-ethylhexyl) monoperoxy carbonate, and the like and mixtures of these initiators. In the precharge, the initiator is dissolved in between about 10 and 90% of the selected solvent and the overall concentration of initiator, or initiator mixture, with respect to total monomer, during the reaction is maintained and controlled to between about 0.2 and about 5 wt. %, preferably between about 0.5 and about 2 wt. %.

In the initial stage of the process, i.e. precharging and introduction of the monomeric component, at which some polymerization takes place, the use of a low temperature initiator or a mixture of low temperature and high temperature initiators is recommended. Such low temperature initiators include diacyl peroxides such as diacetyl peroxide, dibenzoyl peroxide, dilauroyl peroxide; peresters such as t-butylperoxy pivalate, t-butyl peroctoate, t-amylperoxy pivalate, t-butylperoxy-2-ethyl hexanolate; percarbonates such as dicyclo hexyl peroxy dicarbonate, as well as azo compounds such as 2,2'-azo-bis(isobutyrolnitrile) , 2,2'-azo-bis(2,4-dimethylvaleronitrite) ,

2,2 '-azo-bis(cycanocyclohexane) and mixtures thereof, the organic peroxides being preferred. The reaction is carried out under anhydrous conditions in the absence of oxygen which is maintained by purging the reaction zone with an inert gas, such as nitrogen, throughout the reaction. In carrying out the present process, the reactor is precharged under moderate conditions such as a temperature of between about 50° and about 90°C. , preferably for lactam monomer reaction, between about 60° and about 70°C, with a polymerization inducing amount of the low temperature free-radical initiator or high and low temperature initiator mixture dissolved in the nonpolar solvent selected for the reaction. The monomer or monomeric mixture in solution is then introduced, e.g. gradually within a period of 1-6 hours, into the reactor and contacted with the precharged solution under vigorous agitation, e.g. by agitation with high shear mixing device operating at from about 100-800 rpm and the resulting mixture is then heated to reaction temperature at between about 110° and about 150°C. , preferably between about 115° and about 135°C. It is essential that the high temperature initiator be present at this stage of the reaction. Hence, in cases where it is absent in the precharge of initiator solution, the high temperature initiator is introduced at this stage. The pressure in the reactor during polymerization may vary from atmospheric up to 100 psi, more often between about atmospheric and about 50 psi, depending upon the monomeric species selected. Although the total initiator solution can be added as the precharged mixture, it is more desirable to add initiator solution throughout the reaction either by gradual addition or at separate stages of conversion as desired. In the preferred operation, it is best to contact the reaction mixture initially or with additional high temperature initiator solution after at least 50% of the monomers are converted to the polymeric product. The polymerization temperature of this invention is critical since a minimum of 110°C. is needed to activate the high temperature initiator; whereas, above 150°C. , as the temperature approaches the Tg of the polymer, the product is formed as a gelatinous mass in place of the desired finely divided particles.

The polymerization reaction is carried out over a period of from about 2 to about 48 hours, more often a reaction time of from about 6 to about 12 hours is sufficient to achieve complete conversion of the monomeric species. Toward the end of the reaction, the polymerization mixture may become too viscous for good agitation. In this case, additional solvent can be introduced to reduce the solids level below 10%. However, this step is optional. Another expedient which improves contact between the monomer and initiator involves introducing the monomeric species below the level of the initiator solution in the reactor.

After polymerization is completed the reactor is cooled and the contents withdrawn and the solvent removed by drying at a temperature of between about 80°C. and about 120°C. to recover the desired granulated particulate product containing less than 1,000 ppm (less than 0.1 wt. %) , preferably less than 400 ppm, of residual monomer.

A major advantage of this embodiment of the present process is the ability to produce polymer containing no more than trace amounts of lactam residual monomer, in which concentrations it does not alter or dilute the desired polymeric properties and has no toxic affect. Thus, the present products are particularly useful for cosmetic, medicinal and pharmaceutical applications. Another advantage achieved by the present polymerization operation is that the initiator precharge and high reaction temperature permits substantially quantitative conversion to pure homopolymers or to pure copolymers in ratios heretofore unachievable without significant contamination. Further advantages of the present process is the convenience of pure product recovery by solvent stripping.

The process herein also can make fine powders of homopolymers of vinylcaprolactam at a high solids level and in high yield by controlling the amount of vinylcaprolactam monomer in the reaction mixture to preclude excessive build-up of the monomer therein. Free monomer present during such polymerization ordinarily can cause the formation of a gummy polymer product; however, the absence of excessive build-up of monomer in the reaction mixture will enable the preparation of fine polymer powders of polycaprolactam in a yield of at least 95%, preferably 98%, at a very high solids level, suitably at about 17%, and even at 30% or more.

The solvent used herein is one in which polyvinylcaprolactam has a glass transition temperature of at least 100°C. Preferably, the solvent is a C₃-C₂₀ alkane. Other related solvents are not suitable because the polymer has a low glass transition temperature in such solvents. For example, in cyclohexane solvent, only gummy polymer products are obtained.

The monomer feeding rate is 0.75 to 1.5 g monomer/min/1000 g of heptane. At feeding rates higher than about 1.5 g monomer/min/1000 g of heptane, only gummy products are formed, or low yields, whereas fine powders at high yields are obtained within the predetermined feeding rates. Feeding rates slower than 0.75 are impractical. Furthermore, the monomer feed time provides a desired high polymer solids level, suitably at least 120 minutes, and generally 3 to 6 hours, depending upon the selected feed rate. Copolymers of a vinyl pyrrolidone (VP) and acrylamide (AAM) can be made herein by the precipitation polymerization process of the invention in an aliphatic hydrocarbon solvent in the presence of a polymerization initiator.

These monomers may be employed in weight ratios over the entire compositional range of the copolymers, i.e. from 1-99 weight percent vinyl pyrrolidone and 99:1 weight percent of acrylamide. Accordingly, weight ratios of VP:AAM in the copolymer of 99:1, 90:10, 75:25, 60:40, 50:50, 40:60, 25:75, 10:90 and 1:99, for example, may be conveniently prepared in this invention in substantially quantitative yields.

The amount of solvent used in the process of the invention should be sufficient to dissolve an appreciable amount of the reactants and to maintain the copolymer precipitate in a stirrable state at the end of the polymerization. Generally, up to about 40% solids, usually about a 10-20% solids, is maintained in the reaction mixture.

The precipitation polymerization process is carried out in the presence of a polymerization initiator, preferably a free radical initiator, and most suitably, a peroxy ester, e.g. t-butylperoxy pivalate, although other free radical initiators such as acylperoxides, alkyl peroxides and azo-nitriles, known in the art or described in the aforementioned references, may be used as well.

The amount of such initiator may vary widely; generally about 0.2-5.0% is used, based on the weight of total monomers charged.

The reaction temperature may vary widely; generally the reactants are maintained at about 50°-150°C. , preferably 60°-70°C, during the polymerization. Pressure usually is kept at atmospheric pressure, although higher and lower pressures may be used as well. The reaction mixture should be stirred vigorously under an inert atmosphere, e.g. nitrogen, during the polymerization. A stirring rate of about 400-600 rpm in a 1-liter lab reactor is quite adequate to effect the desired polymerization and to keep the precipitate in a stirrable state during the polymerization.

The monomers and initiator used herein are commercially available materials, as described below.

The precipitation polymerization process of the invention may be carried out by first precharging a suitable reactor with predetermined amounts of vinyl pyrrolidone and acrylamide monomers in the aliphatic hydrocarbon solvent, and heating the solution to a desired reaction temperature while stirring vigorously under an inert gas atmosphere. The initiator is then charged into the reactor. Then the reaction mixture is held for an additional period of time for polymerization to occur. Finally, the mixture is cooled to room temperature. Filtering, washing with solvent, and drying provides the copolymer in yields approaching quantitative, and, substantially, in a composition predetermined by the weight ratio of monomers introduced into the reactor. Alternatively, the aliphatic hydrocarbon solvent and acrylamide monomer can be precharged into the reactor, purged with nitrogen, heated to reaction temperature, the initiator added, and then vinyl pyrrolidone monomer is introduced over a period of time into the precharged reactor.

TABLE I

P(VP/AAM) SOLUBILITY (2% SOLUTION)

VP/AAM W/W 90/10 75/25 60/40 50/50 40/60 25/75 10/9

P = Polymer

VP = Vinyl Pyrrolidone

AAM = Acrylamide

W/W = Weight to weight

S = Soluble

I = Insoluble

In accordance with another feature of this invention, there is provided a non-aqueous, liquid phase process for forming discrete particles, most desirably in powder form, of a silicon compound encapsulated in a water-soluble or water-swellable polymer, which process comprises precharging a reactor at between about 50° and about 80°C. with a polymerizing amount of a free radical initiator and a non-polar solvent in an amount sufficient to solubilize a selected silicon compound; adding to the precharged reactor, the silicon compound under vigorous agitation and gradually introducing from about 50 to about 99 wt. %, based on silicon compound, of a polymerizably precipitatable, aliphatically unsaturated monomer at a controlled rate; continuously polymerizing the monomer, under vigorous agitation with the silicon compound, at between about 50 and about 165°C. while maintaining^"a desired monomer level of not more than 10% in the reactor and recovering a solid particulate product of silicon droplets entrapped in said polymerized monomer by separation from the reaction mixture.

The order of addition as precharge is critical to the formation of polymeric particles; however, the silicon compound and the monomeric component can be introduced simultaneously or separately into the precharged reactor. When the monomeric component is introduced separately, it has been found beneficial, but not essential, to feed the monomer below the surface of the liquid reaction mixture containing dissolved silicon compound to promote better contact. Also, an excess of the monomeric component, e.g. from about 50 to about 99 wt. % based on the silicon compound, is preferred in the present process. The most desirable weight ratio of monomer to silicon compound is between about 4:1 and about 8:1.

The silicon compounds, primarily silanes, siloxanes and silanols, used in the present invention are those which are soluble in a non-polar organic solvent and are solids or non-volatile liquids having a viscosity of between about 5 and about 600,000 centistokes (cs) at 25°C. These include polyalkyl siloxanes, polyaryl siloxanes, hydroxylated and/or halogenated polyaryl- or polyalkyl- siloxanes, polyalkaryl siloxanes, polyether siloxane copolymers and alkylene acrylate* derivatives of

* "Acrylate" or "acrylic" as used herein, is intended to include both unsubstituted acrylate and methacrylate or unsubstituted acrylic and methacrylic compounds. polyalkyl-, polyaryl- or polyalkaryl- siloxanes as well as trialkyl silanols, silicon halides such as hexachloro polysilane, hexaaryl polysilanes and other silicon containing compounds having a boiling point greater than about 165°C. , species of which are disclosed in U.S. Patents 2,826,551; 3,964,500 and 4,364,837 as well as in British Patent 849,433; all incorporated herein by reference.

Preferred of these silicon compounds are those having a viscosity of from about 100 to about 100,000 cs which are described by the formula

wherein n has a value of from 0 to 50, R^, R₂, R₃ and R₄ are each individually hydrogen, chloro, bromo, hydroxyalkyl, lower alkyl or phenyl and wherein R₃ alternatively can be alkylene acrylate. These compounds can be employed individually, in admixtures or as silicon copolymers, for example, poly[ (dimethylsiloxane) / (diphenylsiloxane) ] , and other combinations of the above designated species. Examples of these preferred silicon compounds include polydimethyl siloxanes, polymethylphenyl siloxanes, polymethylsilanols, tetramethylbis(chloromethyl) disiloxane, trimethyloxy silyl propyl methacrylate, trimethyloxy silyl methyl methacrylate etc. Of these, the polydimethylsiloxanes are most preferred.

The silicon solubilizing solvents employed herein include linear, branched or cyclic alkanes having from 2 to 20 carbon atoms; although cyclohexane and heptane are particularly recommended. The silicon compound is intimately mixed and dissolved in the selected solvent at a temperature of from about 50° to about 80°C. Generally the silicon solution formed in the reactor contains from about 0.5 to about 50%, preferably from about 0.5 to about 10%, of dissolved silicon compound.

The aliphatically unsaturated monomer employed in the present invention can be an individual monomeric compound or it can be a mixture of copolymerizable monomers which are soluble in the reaction mixture and which form a water-soluble or water-swellable precipitate when polymerized. These monomeric components include acrylic acids, acrylamide, N-vinylpyrrolidone, N-vinylcaprolactam, alone or in admixture with less than 50% of a comonomer such as a C^ to C₄ alkyl acrylate, an acrylic acid, vinyl acetate, N,N-dimethylaminoethyl methacrylate, N,N-dimethylaminomethyl acrylate, N,N-dimethylaminopropyl methacrylate, N,N-dimethylaminopropyl methacrylamide, N,N-dimethylaminoethyl acrylamide or a crosslinking agent such as N,N-divinylimidazolidone, the divinyl ether of diethylene glycol, pentaerythritol triallyl ether, triallyl-1,3,5-triazine-2,4,6-(1H,3H,5H)trione, ethylene glycol diacrylate, 2,4,6-triallyloxy-l,3,5-triazine, 1,7-octadiene, 1,9-decadiene, divinyl benzene and methylene bis(acrylamide) or any other comonomer which is capable of forming with the primary monomer a macro- or micro- cellular polymeric structure around the silicon molecule.

Generally the monomer or monomeric mixture is introduced into the precharged reactor at a controlled rate, with high shear mixing over an extended period depending on the solvent employed. The reaction mixture requires vigorously agitation under an inert atmosphere, e.g. a nitrogen atmosphere, during polymerization. A stirring rate of from about 100 to about 800 rpm is generally adequate to keep the monomeric species uniformly distributed and the polymeric precipitate product dispersed throughout the polymerization reaction. In a preferred embodiment, the polymerization reaction is carried out in a low and a high temperature stage, i.e. the later stage of polymerization is effected at a higher temperature of between about 100° and about 165°C, most preferably between about 110° and about 130°C. , as opposed to the formation of the silicon solution, and early stage of polymerization at 50 to 80°C. , preferably at 60° to 70°C.

At the high temperature level, the monomer concentration in the reactor is controlled to below 2%, more desirably below 1%, as can be determined by iodine titration. Further, the precipitated solids level in the reaction should be maintained at between about 10% and about 50%, preferably between about 15% and about 30%.

When the entire reaction is carried out at a temperature below 100°C, with a low temperature initiator, the monomer concentration in the polymerizing mixture can be allowed to rise to about 10%, more desirably to about 6%.

These limits of monomer concentration are critical since it is discovered that monomer levels above 10% in the low temperature operation, or monomer levels at or above 2 . in the high temperature operation produce non-particulate, gummy, gelatinous products which are difficult to handle and purify. Accordingly, the feed rate of the monomeric component is also critical to the success of the process and is controlled to between about 0.08 and about 2.5 g/minute/1000 g. of solvent. In preferred embodiments of the invention, N-vinyl pyrrolidone or cross-linking agent and N-vinyl pyrrolidone feed rate of from about 0.8 to about 1.3 g/minute/1000 g. of cyclohexane or from about 0.2 to about 0.8 g/minute/1000 g. of heptane, are employed to obtain a particulate product in fine powdery form. The monomeric component is introduced over a period of from about 2 to about 15 hours in order to achieve a desired high polymer solids level in the reactor, e.g. between 10 and 50%.solids, preferably between 15 and about 30% solids.

The polymerization initiator of in the present reaction, which is precharged to the reactor at a temperature of between about 50 and about 80°C, is a low temperature, free radical initiator or, when the reaction is partially conducted at 100°C. or above, can be a mixture of low and high temperature initiators, employed in catalytic amount, for example, between about 0.2 and about 15%, preferably between about 1 and about 5%, based on the weight of total monomer charged. Suitable low temperature initiators are represented by the free-radical polymerization inducing peroxides such as hydrogen peroxide, diacyl peroxides such as diacetyl peroxide, dibenzoyl peroxide, dilauroyl peroxide; peresters such as t-butylperoxy pivalate, t-butyl peroctoate, t-amylperoxy pivalate, t-butylperoxy-2-ethyl hexanolate; percarbonates such as dicyclo hexyl peroxy dicarbonate, as well as azo compounds such as 2,2'-azo-bis(isobutylronitrile) , 2,2'-azo-bis(2,4-dimethylvaleronitrite) , 2,2 '-azo-bis(cycanocyclohexane) . However, the organic peroxides are more desirably recommended.

Preferred operation involves continuously metering the initiator or introducing the initiator at several stages or intermittently during the polymerization reaction. However, when the temperature of the reaction is raised to 100°C. and above, high temperature initiators, having a half life of at least 10 hours at 100°C. or above, are employed. Representative examples of these high temperature initiators include, 2,5-dimethyl-2,5-di- (t-butylperoxy) hexane, di-t-butyl peroxide, dicumyl peroxide, t-butylcumyl peroxide, t-butylperoxy maleic acid, t-butyl hydroperoxide, 2 , 2-di (t-butylperoxy) butane, ethyl-3 , 3-di(t-butylperoxy) butyrate, t-butyl peroxy acetate, t-butylperoxy benzoate and the like. Thus, in the preferred operation, the reactor is precharged with a low temperature initiator, the silicon and monomer(s) are introduced and polymerization takes place at a temperature of between about 50° and about 80°C. , e.g. 60-70°C. Subsequently, e.g. after about 2 hours or more, the reaction temperature is raised to 100°C. or above, most preferably to 110-130°C. and a high temperature initiator is introduced at one or more stages, to complete the reaction. It has been found that at the higher temperatures, above about 100°c, products containing substantially less than 2%, usually less than 1% monomer are produced. Also, the gradual or intermittent introduction of initiators throughout the polymerization reaction insures high conversion of monomer.

The present reaction is carried out under a pressure ranging from about atmospheric to about 80 psig with thorough mixing until the desired amount of polymeric precipitate has been formed. Because of the vigorous mixing and the controlled feed rate of monomeric component, a polymeric film is formed around a molecule of the silicon compound so as to entrap droplets of the silicon within the particulate polymeric structure. Of course, it is understood that during the reaction, some molecules of the silicon may adhere to the external surface of the polymeric structure as well. This effect may take place when larger amounts of the silicon component are employed. However, such occasional attachment does not detract from the water solubility or water-swellability of the polymeric portion of the particulate product. After the reaction is completed, the solids are removed from the reactor and recovered by filtration, decantation or by any other convenient means and the recovered solids are dried to produce discrete white particles, which, in most cases, have an average particle diameter of from about 40 to about 450 micrometers. The particulate product of this invention contains between about 1 and about 50%, preferably between about 10 and about 20% silicon compound, depending upon the feed ratio of the silicon to monomeric component.

The silicon-containing products of the present invention combine the valuable properties of both the silicon compound and the polymeric encapsulating agent, which properties include flexibility, hair and skin substantivity, thermal stability, oxygen permeability, etc. as well as providing glossy, lustrous coatings having excellent release properties.

The use of the silicon products in hair formulations such as shampoos, conditioners, hair dyes or bleaches, hair structure altering compositions, is particularly desirable for their lusterous effects. Generally, between about 8 and about 30 wt. %, preferably between about 10 and about 20 wt. %, of non-crosslinked polymer and between about 0.5 and about 10%; preferably between about 1 and about 8%, of crosslinked polymer imparts high gloss when incorporated into a standard hair or skin formulation, particularly a shampoo or conditioning formulation. These formulations, of course, may also include other adjuvants such as perfumes, essential oils, dyes and the like to enhance commercial acceptability. A typical lusterizing shampoo composition may contain the following components. Wt .

Silicon in Crosslinked Polymer

Silicon in Non-Crosslinked Polymer

Hair bodying component

Suds booster

Ethanol

Water

Amphoteric detergent

Perfume, colorant, UV Absorber

Another use for the present products is in the field of commercial thickeners which are added to compositions in oil recovery, textiles and detergents.

EXAMPLE 1

In a 2-liter, 4-necked reaction kettle equipped with a condenser, a constant speed (set at 170 rpm) mechanical stirrer with torque reading and anchor agitation (open radius of 4 and 5/6 inches) , 2 dip tubes connected to 2 separate metering pumps, a nitrogen purge adaptor and a thermocouple connected to the temperature controller, 1,000 grams of heptane were charged and the reactor was heated to 65°C. in 60 minutes with nitrogen purge throughout the entire process. The reactor was held at 65°C. for 30 minutes, after which 520 microliters of t-butylperoxy pivalate (Lupersol 11) was added followed by addition of a solution of 150 grams of N-vinylpyrrolidone and 50 grams of acrylic acid over a period of 4 hours. After completion of the addition, the resulting solution was transferred to a 2 liter stainless steel high pressure reactor and 1 gram of 2 , 5-dimethyl-2 , 5-di (t-butylperoxy) hexane was added. The resulting mixture was heated to 130°C. under 50 psig within one hour and held at that temperature for an additional 8 hours with constant agitation. The reaction mixture was then cooled to room temperature and the reactor contents transferred to an oven wherein it was dried at 100°C. for 16 hours and then in a vacuum oven at 90°C. for an additional 16 hours after which a white powdery product of non-crosslinked poly(vinylpyrrolidone/acrylic acid) copolymer containing 0.04% (400 ppm) of total residual monomer, was recovered.

EXAMPLE 2

Example 1 was repeated except that cyclohexane was substituted for heptane. The white powdery N-vinylpyrrolidone/acrylic acid copolymer product obtained in this Example had a residual monomer content of 300 ppm.

EXAMPLE 3

1 gram of 2,5-dimethyl-2,5-di(t-butylperoxy) hexane was used into the process of Example 1. The reactor was held at 65°C. for 30 minutes after which 520 microliters of t-butylperoctoate was added followed by addition of 150 grams of N-vinyl caprolactam and 50 grams of acrylic acid over a period of 4 hours. The reactants were reacted at 130°C. under 50 psig over a period of 8 hours with constant agitation, and further treated as in Example 1. A white powdery product of poly(vinyl caprolactam/acrylic acid) , containing about 500 ppm residual monomer was recovered. EXAMPLE 4

Into a 2 liter, stainless steel reactor equipped with a condenser, a mechanical stirrer, 2 tubes connected to separate metering pumps, a nitrogen purge and a thermocouple connected to the temperature controller, are charged 1,000 grams of heptane and 520 microliters of t-butylperoxy pivalate (Lupersol 11) and the reactor heat to 65°C. in 60 minutes with nitrogen purge throughout the entire process. Example 1 was followed with a solution o 200 grams of N-vinylpyrrolidone added over a period of 4 hours. After completion of the addition, 1 g of 2,5-dimethyl-2,5-di- (t-butylperoxy) hexane (Lupersol 101 is added and the resulting solution is heated to 130°C. under a developed pressure of 50 psi within one hour and held at that temperature for an additional 8 hours with constant agitation. The reaction mixture is then cooled room temperature and the reactor contents transferred to oven wherein it was dried at 100°C. for 16 hours and then in a vacuum oven at 90°C. for an additional 16 hours afte which a white powdery homopolymeric product of non-crosslinked poly(vinylpyrrolidone) containing 0.02% (200 ppm) of residual monomer, is recovered.

EXAMPLE 5

520 microliters of a 50/50 mixture of dicumyl peroxide and t-butylperoxy pivalate (Lupersol 11) and the reactor is heated to 65°C. in 60 minutes with nitrogen purge throughout the entire process. The reactor is held at 65°C. for 30 minutes, after which is added a solution 185 grams of N-vinylpyrrolidone and 15 grams of styrene over a period of 4 hours. After completion of the addition, the resulting solution is heated to 130°C. unde 60 psi within one hour and held at that temperature for an additional 10 hours with constant agitation. The reaction mixture is then cooled to room temperature and the reactor contents transferred to an oven wherein it was dried at 100°C. for 16 hours and then in a vacuum oven at 90°C. for an additional 16 hours after which a white powdery product of non-crosslinked poly(vinylpyrrolidone/styrene) copolymer containing a trace of residual monomer, is recovered.

EXAMPLE 6

As in Example 1, the reactor is held at 90°C. for 30 minutes, after which 450 microliters of a 50/50 mixture of t-butylperoxy pivalate (Lupersol 11) and t-butylperoxy benzoate is added followed by addition of a solution of 150 grams of acrylamide over a period of 4 hours. After completion of the addition, the resulting solution was transferred to a stainless steel reactor equipped with a mechanical stirrer and heated to 120°C. under 40 psi within one hour holding at that temperature for an additional 6 hours with constant agitation and an additional 70 microliters of t-butylperoxy benzoate initiator is then added and the reaction continued under agitation at 120°C. for an additional 3 hours. The reaction mixture then cooled to room temperature and the reactor contents transferred to an oven wherein it was dried at 100°C. for 16 hours and then in a vacuum oven at 90°C. for an additional 16 hours after which a white powdery product of non-crosslinked polyacrylonitrile containing 0.05% (500 ppm) of residual monomer, is recovered. EXAMPLE 7

Into a 2 liter, stainless steel reactor equipped with a condenser, a mechanical stirrer, 2 tubes connected to separate metering pumps, a nitrogen purge tube and a thermocouple connected to the temperature controller, are charged as in Example 1, 1,000 grams of heptane, and 15 grams of acrylamide are charged and the reactor heated to 90°C. in 60 minutes with nitrogen purge throughout the entire process. The reactor is held at 90°C. for 30 minutes, then 520 microliters of a 50/50 mixture of dicumyl peroxide and t-butylperoxy pivalate (Lupersol 11) is added after which a solution of 185 grams of acrylic acid is introduced over a period of 4 hours. After completion of the addition, the resulting solution is heated to 130°C. under 60 psi within one hour and held at that temperature for an additional 10 hours with constant agitation. The reaction mixture is then cooled to room temperature and the reactor contents transferred to an oven wherein it was dried at 100°C. for 16 hours and then in a vacuum oven at 90°C. for an additional 16 hours after which a white powdery product of non-crosslinked poly(acrylic acid/acrylamide) copolymer containing a trace of residual monomer, is recovered.

EXAMPLE 1

A 2-liter, four-necked reaction kettle (bottom radius = 5-1/8 inches) equipped with a condenser, a constant speed mechanical stirrer at 170 rpm with torque reading and anchor agitator (open radius = 4-5/6 inches) , one dip tube connected to a metering pump, a nitrogen purge adaptor, and a thermocouple connected to a temperature controller, was charged with 1000 grams of heptane. The reactor then was heated to 65°C. in 30 minutes while purging with nitrogen, held at 65°C. for 30 minutes and 52 microliters of t-butylperoxypivalate (Lupersol 11) was added. Then a solution of 200 g of vinylcaprolactam prepared by melting the solid monomer at a 65°C. water bat temperature and adding 50 g of heptane was fed into the reactor over a predetermined period of time (see below) . Finally 200 microliters of additional t-butylperoxypivalat was charged into the reactor and the reaction mixture, under stirring, was kept overnight at 80°C. Then the contents were cooled to room temperature and filtered. The polymer reaction product was a white powder cake which was dried successively in a hood, in an oven at 100°C. , and in a vacuum oven at 90°C, for 16 hours each.

TABLE II

Feed Rate (g monomer/ min/1000 g

VP (g) Feed Time (hrs) of heptane Yield % Solids Product *K-val

200 1.1 100 16.7 Fine powder 42.6

200 0.75 100 16.7 Fine powder 40.0

200 1.5 100 16.7 Fine powder 42.6

200 1.1 100 16.7 Fine powder 40.9

200 1.1 98 28.6 Fine powder 41.8

200 1.5 1.9 Gum

* Fikentscher values : measured in a 1% aqueous solution at 25°C.

EXAMPLE 9

The procedure of Example 8 was followed using cyclohexane in place of heptane. The results show that even at a low feeding rate only gummy products are obtained.

TABLE III

Feed Rate (g monomer/ min/1000 g VP (g) Feed Time (hrs) of cyclohexane) Yield % Solids Product

200 0 . 75 Gum

EXAMPLE 10

1. PREPARATION OF COPOLYMERS OF VINYL PYRROLIDONE AND ACRYLAMIDE

A 1-liter, 4-necked reaction kettle was equipped with a mechanical stirrer, thermometer, dropping funnel and a nitrogen purge tube. The reactor was precharged with 45 g. of vinyl pyrrolidone and 5 g. of acrylamide in 500 g. of cyclohexane. The solution then was heated to 65°C. during 20 minutes and held there for 30 min. , while stirring under nitrogen gas. Then 210 microliter (0.2 g.) of t-butylperoxy pivalate initiator was added. The reaction was stirred overnight at 65°C.

The reaction product then was cooled to room temperature. A fine white powder precipitate of copolymer product was obtained which was filtered, washed twice with heptane and dried overnight at 100°C. and then for two days in a vacuum oven at 190°C.

A 90:10 VP:AAM copolymer (wt. ratio) was obtained in 100% yield and a nil level of residual monomer.

EXAMPLES 11-16

The procedure of Example 10 was followed using 37.5, 30, 25, 20, 12.5 and 5 g. of vinyl pyrrolidone and 12.5, 20, 25, 30, 37.5, and 45 g. of acrylamide, to produce the corresponding 75:25, 60:40, 50:50, 40:60, 25:75 and 10:90 wt. ratio VP:AAM copolymers in yields approaching 100% and a residual monomer level below 1%.

EXAMPLES 17-18

The procedure of Examples 10-16 was followed using hexane and heptane in place of cycloheptane, with similar results. EXAMPLE 19

The procedure of Examples 10-18 was repeated using a continuous feed of a stream of VP into the AAM solvent-charged reactor at 65°C. to provide the copolymer in 95-100% yield.

EXAMPLE 20

The procedure of Examples 10-19 were followed using vinyl caprolactam in place of VP with similar results.

EXAMPLE 21

In a 2-liter, four-necked reaction kettle equipped with a condenser, a constant speed (set at 170 rpm) mechanical stirrer with torque reading and anchor agitator (open radius = 4 and 5/6 inches) , two dip tubes connected to two separate metering pumps, a nitrogen purge adaptor, and a thermocouple connected to the temperature controller, 1000 grams of cyclohexane were charged and the reactor was heated to 65°C. in 30 minutes with nitrogen purge throughout the entire process. The reactor was held at 65°C. for 30 minutes, after which 520 microliters of t-butylperoxy pivalate (Lupersol 11) was added followed by addition of a solution of 250 grams of vinylpyrrolidone (VP) , 1.25 grams of pentaerythritol triethyl ether crosslinking agent and 25 grams of silanol terminated polydimethyl siloxane were added to the reactor over a period of 4 hours at a rate of 1-1.1 ml/minute) . After completion of the addition, the resulting mixture was stirred at 65°C. overnight and thereafter heated to 85°C. for 1 hour after which t-butylperoxide pivalate (200 microliters) were charged each hour for an additional 4 hours at 85°C. to complete the reaction. The reaction mixture was then cooled to room temperature, after which i was dried in an oven at 100°C. for 16 hours and then in a vaccum oven at 90°C. for an additional 16 hours, whereupon 98% yield of a white powdery product in which at least 80% of the silicone compound was entrapped in a crosslinked polyvinylpyrrolidone matrix is recovered.

EXAMPLE 22

Example 21 was repeated, except that 1000 g. of heptane was substituted for 1000 g. of cyclohexane; 1.25 g of divinyl imidazolidone crosslinking agent and a feed rate of 0.5-0.55 ml/minute was substituted for pentaerythritol triethyl ether and a feed rate of 1-1.1 ml/minute.

The product of this example was recovered in 98% yield as a white powder in which at least 80% of the silicone compound was encapsulated in the crosslinked polyvinylpyrrolidone matrix.

EXAMPLE 23

1000 grams of cyclohexane were charged and the reactor was heated to 65°C. in 30 minutes with nitrogen purge throughout the entire process. The reactor was held at 65°C. for 30 minutes, after which 520 microliters of t-butylperoxy pivalate (Lupersol 11) was added followed by addition of a solution of 250 grams of vinylpyrrolidone and 75 grams of Dow Corning 200 silicone fluid of 200 cs viscosity* were added to the reactor over a period of 4 hours at a rate of l-l.l ml/minute). After completion of the addition, the resulting mixture was stirred at 65°C.

* DC 200 polydimethyl siloxane overnight and thereafter heated to 85°C. for 1 hour after which t-butylperoxide pivalate (200 microliters) were charged each hour for an additional 4 hours at 85°C. to complete the reaction. The reaction mixture was then cooled to room temperature, after which it was dried in an oven at 100°C. for 16 hours and then in a vaccum oven at 90°C. for an additional 16 hours, whereupon 94% yield of a white powdery product in which at least 90% of the silicone compound was entrapped in the non-crosslinked polyvinylpyrrolidone matrix is recovered.

EXAMPLE 24

Example 23 was repeated except that 150 g of DC 200 was substituted for 75 g. of DC 200. The identical silicone encapsulated product was recovered in 92% yield.

EXAMPLE 25

Example 23 was repeated except that 25 g. of silanol terminated polydimethylsiloxane was substituted for 75 g. of DC 200. The identical silicone encapsulated product was recovered in 90% yield.

EXAMPLE 26

Example 23 was repeated except that 1000 g. of heptane was substituted for 1000 g. of cyclohexane, a feed rate of 0.5-0.55 ml/minute for VP and DC 200 was used instead of 1-1.1 ml/minute. The identical silicone encapsulated product was recovered in 96% yield. EXAMPLE 27

1000 grams of heptane were charged and the reacto was heated to 65°C. in 30 minutes with nitrogen purge throughout the entire process. The reactor was held at 65°C. for 30 minutes, after which 520 microliters of t-butylperoxy pivalate (Lupersol 11) was added followed by addition of a solution of 250 grams of N-vinyl caprolactam and 50 g. of monomethacryloxypropyl terminated polydimethylsiloxane over a period of 3 hours at a rate of 1.5 ml/minute). After completion of the addition, the resulting mixture was stirred at 65°C. overnight and thereafter heated to 85°C. for 1 hour after which t-butylperoxide pivalate (200 microliters) were charged each hour for an additional 4 hours at 85°C. to complete the reaction. The reaction mixture was then cooled to roo temperature, after which it was dried in an oven at 100°C. for 16 hours and then in a vaccum oven at 90°C. for an additional 16 hours, whereupon 92% yield of a white powdery product in which at least 80% of the silicone product was entrapped in a non-crosslinked polyvinyl caprolactam matrix is recovered.

EXAMPLE 28

1000 grams of heptane were charged and the reactor was heated to 65°C. in 30 minutes with nitrogen purge throughout the entire process. The reactor was held at 65°C. for 30 minutes, after which 520 microliters of t-butylperoctate was added followed by addition of a solution of 250 grams of N-vinyl pyrrolidone and 50 g. of monomethacryloxypropyl terminated polydimethylsiloxane over a period of 7 hours at a rate of 0.6 ml/minute). After completion of the addition, the solution was transferred to a 2 liter stainless steel high pressure reactor and 1 gram of 2,5-dimethyl-2,5-di(t-butylperoxy) hexane added. The resulting mixture was then heated to 130°C. under 50 psi. within l hour and held at that temperature for 8 hours with constant agitation. The reaction mixture was then cooled to room temperature and the reactor contents transferred to an oven wherein it is dried at 100°C. for 16 hours and then in a vaccum oven at 90°C. for an additional 16 hours, whereupon a white powdery product containing less than 0.1% monomer and in which at least 80% of the silicone compound was entrapped in a non-crosslinked polyvinyl pyrrolidone matrix is recovered.

EXAMPLE 29

1000 grams of heptane and 20 g. of monomethacryloxypropyl terminated polydimethylsiloxane were charged and the reactor was heated to 65°C. in 30 minutes with nitrogen purge throughout the entire process. The reactor was held at 65°C. for 30 minutes, after which 520 microliters of t-butylperoxy pivalate (Lupersol 11) was added followed by addition of a solution of 280 grams of N-vinyl caprolactam was introduced over a period of 3 hours at a rate of 1.5 ml/minute). After completion of the addition, the resulting mixture was stirred at 65°C. overnight and thereafter heated to 85°C. for 1 hour after which t-butylperoxy pivalate (200 microliters) were charged each hour for an additional 4 hours at 85°C. to complete the reaction. The reaction mixture was then cooled to room temperature, after which it was dried in an oven at 100°C. for 16 hours and then in a vaccum oven at 90°C. for an additional 16 hours, whereupon 95% yield of a white powdery product in which at least 85% of the silicone product was entrapped in a non-crosslinked polyvinyl caprolactam matrix, is recovered.

Claims

WHAT IS CLAIMED IS:

1. A precipitation polymerization process for making homopolymers, copolymers and polymers mixtures with other comonomers, of a precipitable, aliphatically unsaturated monomer, preferably as fine powders, at a high solids level, in high yield, having a low residual monomer content, optionally with entrapped silicon compounds, which comprises:

(1) preparing a particulate polymeric product containing less than 1,000 ppm residual monomer, by the steps of:

(a) precharging a reactor with a polymerizing amount of a mixture containing a low temperature, free-radical initiator dissolved in a non-polar inert solvent to provide an initiator solution;

(b) contacting a non-polar polymerizably precipitatable monomeric component with said precharged solution at a temperature between about 50° and about 90°C. ;

(c) polymerizing said monomeric component to completion under agitation in the presence of a high temperature free radical initiator having at least a 10 hour half life at 100°C. at a temperature of between about 110° and about 150°C. under a pressure from about atmospheric to about 100 psi and

(d) recovering a particulate polymeric product containing less than 1,000 ppm lactam residual monomer; or

(2) producing homopolymers of polyvinyl caprolactam in the form of fine powders during polymerization of vinyl caprolactam at a solids level of at least about 17% and in a yield of polymer of at least 95%, which comprises precharging a reactor with a predetermined amount of a solvent which is a C₃-C_2Q alkane which, is a non-solvent for the polymer effecting little or no plasticization, and a polymerization initiator, and feeding vinyl caprolactam monomer as a solution in said solvent into said precharged reactor at a rate of 0.75 to 1.5 g vinyl caprolactam/min/lOOO g of said solvent during the polymerization during a feed period of at least 120 minutes which provides the desired level of solids in the product; or

(3) making fine, white, powdered copolymers of vinyl lactam and acrylamide in a yield of greater than 90% which comprises copolymerizing vinyl lactam and acrylamide monomers in a weight ratio of between about 1:99 to 99:1, respectively, in an aliphatic hydrocarbon solvent in the presence of a polymerization initiator; or

(4) encapsulating silicone droplets in a water soluble or water swellable polymer under anhydrous, oxygen free conditions by

(a) precharging a reactor with a reaction solvating amount of a non-polar hydrocarbon solvent and an effective polymerization promoting amount of a free radical polymerization initiator at a temperature of from about 50° to about 80°C ;

(b) feeding to said precharged reactor a silicon compound which is soluble in said solvent and gradually introducing to said reactor, over a period of several hours with vigorous agitation, between about 50 and about 99 wt. %, based on said silicon compound, of a polymerizably precipitatable, aliphatically unsaturated monomer; such as vinyl pyrrolidone or vinyl caprolactam;

(c) continuously polymerizing said monomer and precipitating polymer under vigorous agitation with said silicon compound at a temperature of from about 50° to about 165°C. while maintaining the precipitated solids level at between about 10% and about 50% and the monomer level below about 10% in the reactor; (d) separating precipitated polymer containing entrapped silicon compound droplets from the reaction mixture and

(e) drying said precipitate to a particulate product.

2. The process of claim 1 wherein in (a) the concentration of said high temperature initiator in said reaction mixture is maintained at from about 0.2 to about 5 wt. % and at least a portion of the high temperature initiator is added to the system in the precharge in admixture with said low temperature initiator.

3. The process of claim 1 wherein said precharge consists of low temperature initiator and said high temperature initiator is added to the reaction mixture when the temperature is raised to between about 110°C. and about 150°C, said monomeric species contains vinyl pyrrolidone or N-vinyl caprolactam, a portion of said high temperature initiator is added in said solvent to the reaction mixture after at least 50% of the monomeric component is converted to polymer, the solvent is cyclohexane or heptane, and the monomeric component is gradually added over a period of from about 1 to 6 hours.

4. A process according to claim 1 wherein in (2) said solvent is a C - ₁₀ saturated hydrocarbon, branched or unbranched, cyclic or acylic, such as heptane, hexane or cyclohexane, which includes the steps of precipitating the copolymer as a fine, white powder from solution, filtering and drying, wherein the polymerization is carried out at about 50°-150°C, under an inert gas, with agitation, wherein the solvent is present in an amount sufficient to keep the reactants in solution during the polymerization and to keep the copolymer precipitate in a stirrable state, said vinyl lactam is vinyl pyrrolidone or vinyl caprolactam, and optionally, the vinyl lactam, acrylamide and solvent are precharged in a reactor, or the acrylamide and solvent are precharged and the vinyl lactam is introduced into the reactor.

5. The process of claim 1 wherein in (4) said silicon compound and said monomer are simultaneously fed into said precharged reactor, or wherein said silicon compound is first fed into the reactor followed by the addition of said monomer.

6. The process of claim 1 wherein in (4) said silicon compound has the formula

R₃-f-SiO)_nSi-R₄ ^R2 ^R2

wherein n has a value of from 0 to 50, R-^, R₂ , R₃ and R₄ are each individually hydrogen, chloro, hydroxyalkyl, lower alkyl or phenyl and R₃ can also be an alkylene acrylate, said monomer is selected from the group of acrylic acid, acrylamide, N-vinyl pyrrolidone, N-vinyl caprolactam and mixtures of N-vinyl pyrrolidone and N-vinyl caprolactam, optionally with a polyfunctional polymerizable comonomer selected from the group of an acrylic acid, vinyl acetate, a C-^ to C₄ alkyl acrylate, N,N-dimethylamino- ethyl methacrylate, N,N-dimethylaminomethyl acrylate, and N,N-dimethylaminopropyl methacrylate, optionally with a crosslinking agent selected from the group of triallyl-1,3,5-triazine-2,4,6-(1H,3H,5H)trione, N,N-divinyl-2-imidazolidone, the divinyl ether of diethylene glycol, 2,4,6-triallyloxy-l,3,5-triazine, ethylene glycol diacrylate, 1,7-octadiene, divinyl benzene, 1,9-decadiene, methylene bis(acrylamide) and pentaerythritol triallyl ether.

7. The process of claim 6 wherein said monomer is N-vinyl pyrrolidone optionally containing less than 50% cross-linking agent and the monomer is fed to said precharged reactor at a rate of from about 0.3 to about 0.8 g/minute/1000 g. of said heptane, wherein the entire reaction is carried out at a temperature below 100°C. in the presence of a low temperature free-radical peroxide initiator and the monomer concentration in the reactor is maintained below 6%, wherein the concentration of silicon compound in said solvent is between about 0.5 and about 10 wt. %.

8. The encapsulated silicon powdered product of claim 1 (4) .