Abstract: A high refractive index, foldable polymer suitable for use in ophthalmic devices, such as intraocular lenses, is provided. The polymer may be produced from a polymerization reaction of first, second and third monomeric components and a crosslinking agent. The first monomeric component includes an aryl acrylate or an aryl methacrylate. The second monomeric component, which is not an acrylate, includes a monomer having an aromatic ring with a substituent having at least one site of ethylenic unsaturation. The third monomeric component includes a high water content hydrogel-forming monomer. The resulting high refractive index copolymer is durable enough to be cut and polished when dry, and becomes soft and foldable when hydrated.

Abstract: In vivo polymerizable intraocular lens compositions which comprise substituted fluoroalkyl or perfluoroalkyl monomers having anionic, cationic, and/or nonionic surface active functionality in the unsaturated fluorophobic ends. The compositions are preferably cured by UV photoinitiation and are useful in repairing torn or detached retinal tissue or forming intraocular lenses in situ.

Abstract: The present invention provides a method for producing a cement dispersant having high percentage in water reduction-rate and appropriate air-entraining property. This method for producing a polycarboxylic acid for a cement dispersant is characterized in that alkylene oxide is added at a specific temperature range.

Abstract: The invention relates to heat-hardenable paint composition which contains (A) vinyl based copolymer of hydroxyl group value from 20 to 200 mg KOH/g, being a copolymer of from 5 to 70 wt % hydroxyl group containing a particularly defined vinyl based monomer and from 95 to 30 wt % other vinyl based monomer (a-2), and (B), a particularly defined 1,3,5-triazine-2,4,6-triscarbamic acid ester, or an oligomer thereof, in which the mol ratio of hydroxyl groups originating from the aforementioned (A) component: NHCOOR groups originating from the aforementioned (B) component in the composition is from 1:3 to 3:1.

Abstract: A process for the preparation of an addition product of a linear telechelic difunctional unsaturated polymer containing terminal functional reactive groups other than vinyl groups, involves simultaneously reacting at least one cyclic olefin of from about 4 to 30 carbon atoms, at least one difunctional acyclic olefin of up to about 30 carbon atoms, and at least one reactant YZ in the presence of at least one olefin metathesis catalyst to prepare an addition product of a linear difunctional unsaturated polymer, wherein YZ is capable of adding to a carbon--carbon double bond under ROMP reaction conditions.

Abstract: Described is a polymerizable organic composition comprising a polyol(allyl carbonate), e.g., diethylene glycol bis(allyl carbonate), and an additive represented by the general formulaR.sub.2 --O--(R.sub.3 O).sub.m --(CH.sub.2 CH.sub.2 O).sub.n-1 --CH.sub.2 CH.sub.2 --Xwherein R.sub.2 is a monovalent organic radical having a terminal ethylenically unsaturated group, e.g., allyl, R.sub.3 O is a divalent radical derived from an epoxide other than ethylene oxide, e.g., butylene oxide, m is a number from 0 to 100, n is a number between 3 and 100, and X is selected from halide, hydroxyl, quaternary ammonium groups, the acid groups acetic acid, sulfonic acid, sulfuric acid, isethionic acid and phosphoric acid, salts of said acid groups, alkoxy groups and carboxylic acid ester groups. The additive is present in the composition in an amount at least sufficient such that a polymerizate, e.g., a plus lens, obtained from said composition is substantially free of tinting defects, e.g., ferns and/or moons.

Abstract: A process for the preparation of an addition product of a linear telechelic difunctional unsaturated polymer containing terminal functional reactive groups other than vinyl groups, involves simultaneously reacting at least one cyclic olefin of from about 4 to 30 carbon atoms, at least one difunctional acyclic olefin of up to about 30 carbon atoms, and at least one reactant YZ in the presence of at least one olefin metathesis catalyst to prepare an addition product of a linear difunctional unsaturated polymer, wherein YZ is capable of adding to a carbon--carbon double bond under ROMP reaction conditions.

Abstract: Mesogens are provided based on substituted unsaturated carboxylic acids such as acrylic and methacrylic acid. Substitution of a variety of hydrophobic tails onto the carboxylic acid or acid derivative via the vinyl carbon proximal to the carbonyl of the carboxylic acid results in mesogens that are capable of forming thermotropic and single-phase lyotropic mesophases over a broad range of compositions. The mesophases can be polymerized to lock in the ordered phases.

Abstract: A crosslinkable composition of a polymeric thermoplastic and/or elastomeric material which is susceptible to scorching when processed at elevated temperatures, prior to crosslinking, in the presence of a free radical initiator, is protected against such scorching by the incorporation therein of a mixture of at least one hydroquinone compound and a sulfur accelerator. This mixture may also contain at least one monomeric allylic, methacrylic, acrylic or diene type coagent. The mixture exhibits a synergistic effect resulting in improved scorch protection for peroxide cured systems when compared with the protection afforded by the components singly.

Abstract: An ocular lens material made of a polymer obtained by polymerizing polymerizable components comprising a monomer of the formula (I): ##STR1## wherein R.sup.1 is a group of the formula: ##STR2## wherein R.sup.2 is a C.sub.1-5 alkylene group, and R.sup.3 is a hydrogen atom or a methyl group, or a group of the formula: ##STR3## wherein R.sup.4 is a direct bond or a C.sub.1-5 alkylene group.

Abstract: Disclosed is a plastic lens formed of a crosslinked polymer obtained by polymerizing or copolymerizing a monomer composition comprising as essential component the following component (A) and/or the following component (B), and optionally a component (C) composed of at least one monomer copolymerizable with the essential component comprising the component (A) and/or the component (B):Component (A):an ester obtained from (1)(a) a diol which is obtained by reducing a dimer of an unsaturated fatty acid having 16-18 carbon atoms and/or (b) a diol which is obtained by reducing a dimer of a lower alcohol ester of an unsaturated fatty acid having 16-18 carbon atoms, and (2) acrylic acid or methacrylic acid; andComponent (B):an ester obtained from (1)(a) a triol which is obtained by reducing a trimer of an unsaturated fatty acid having 16-18 carbon atoms and/or (b) a triol which is obtained by reducing a trimer of a lower alcohol ester of an unsaturated fatty acid having 16-18 carbon atoms, and (2) acrylic acid or met

Abstract: Disclosed are optically clear xerogel polymer compositions containing an interpenetrant.

Abstract: Urea and urethane-containing monomers for contact lens materials are disclosed.

Abstract: Disclosed is a diacylperoxide vinyl ester of the general formula I ##STR1## in which R is an alkylene residue which can be straight-chained, branched or cyclic and which can contain 2 to 10 C atoms or R is an aryl residue, suitable for copolymerization with olefinic unsaturated monomers under conditions in which they do not yet radically decompose.

Abstract: Disclosed are optically clear xerogel polymer compositions containing an interpenetrant.

Abstract: Urea- and urethane-containing monomers for contact lens materials are disclosed.

Abstract: A transparent resin obtained by polymerizing styrene, a methacrylic or acrylic acid ester, a polyfunctional monomer, and if necessary a copolymerizable vinyl monomer in the presence of a molecular weight modifier is suitable for producing a polymer lens having a low specific gravity, and excellent in transparency, edging ability with other good properties.

Abstract: A vinyl acetylsalicylate-vinyl alcohol based copolymer which comprises a structural unit having the following formula (1): ##STR1## and a structural unit having the following formula (2): ##STR2## optionally with at least one member selected from the group consisting of a structural unit having the following formula (3): ##STR3## and a structural unit having the following formula (4): ##STR4## In the copolymer, the amounts of vinyl acetylsalicylate units and vinyl alcohol units, degree of polymerization and the like can be controlled, whereby the efficacy of acetylsalicylic acid can be easily controlled as desired. Therefore, the copolymer is expected to be widely applicable as medicament.

Abstract: Graft copolymers having improved phase binding between the graft base and the grafted-on polymer, are prepared from:a) a grafted-on polymer phase containing one or more monomers from the group consisting of (meth)acrylates of alcohols having 1 to 10 carbon atoms, vinyl esters of saturated aliphatic carboxylic acids having 2 to 10 carbon atoms, olefins, vinyl halides, styrene and styrene derivatives, andb) a peroxy group-containing copolymer phase containing from 0.01 to 20% by weight of an olefinically unsaturated peroxy compound of the general formula I or II ##STR1## where R.sup.1 is a chemical bond or a linear or branched alkyl chain having 1 to 10 carbon atoms or a cycloalkyl group having 3 to 10 carbon atoms, R.sup.2 and R.sup.3 are an alkyl group having 1 to 4 carbon atoms, R.sup.4 is an alkyl group or an alkyl-substituted phenyl group having 3 to 12 carbon atoms, and R.sup.5 is a cycloalkyl group having 3 to 12 carbon atoms, and from 80 to 99.

Abstract: A plastic light conduit of cross-linked polymer material having good light transmitting characteristics, without voids or noticeable bubbles, is disclosed. Also disclosed is a method of manufacture and an apparatus, involving progressive heating of reactive monomer mixture in a tube which is submerged in a progressive reactor utilizing cold oil to maintain a cold, non-reacting zone, and hot water to create a hot zone that causes reaction, while simultaneously carrying away the excess exothermic heat of reaction.

Abstract: A homopolymer or a copolymer comprises a polymerizable compound represented by formula (I):A--X--COCOOR.sub.1 (I)whereinR.sub.1 represents a hydrogen atom, a C.sub.1 -C.sub.5 alkyl group or an aryl group;X represents an oxygen atom, a sulfur atom, --COO-- or --NR.sub.5 --whereinR.sub.5 is a hydrogen atom or a C.sub.1 -C.sub.5 alkyl group;A represents a C.sub.3 -C.sub.18 alkenyl, alkynyl, alkenylaryl or alkenylaralkyl group, or a group represented by: ##STR1## wherein R.sub.2 and R.sub.3, which may be the same or different, independently represent a hydrogen atom or a C.sub.1 -C.sub.5 alkyl group;Y represents an oxygen atom or --NR.sub.4 -- wherein R.sub.4 represents a hydrogen atom or a C.sub.1 -C.sub.5 alkyl group; n is an integer of 1 to 5; m is an integer of 1 to 10; and l is 0 or an integer of 1 to 20;with the proviso that if Y is present, X is not --NR.sub.5 --. Additionally, disclosed are processes of preparing the homopolymer or copolymer as well as the polymerizable compound.

Abstract: A heterofunctional macromer represented by the formula: ##STR1## in which R.sub.1 is H or C.sub.1 -C.sub.4 alkyl; R.sub.2 is a (poly) lactone or (poly) ether chain; X.sub.1 is --COO--, --COOCH.sub.2 CH.sub.2 OCO--, --CONHCOO--, --COOCH.sub.2 CH.sub.2 NH--COO-- or ##STR2## X.sub.2 is --O--, --COO-- or --OCO--NH--R.sub.3 --NHCOO-- group; R.sub.3 is C.sub.1 -C.sub.6 alkylene, aromatic or alicyclic group; A is --CH.sub.2 --, --C(CH.sub.3).sub.2 -- or ##STR3## and reactive polymers derived from said macromer.

Abstract: An allyl ester oligomer composition having a viscosity of 200 to 50,000 cP at 30.degree. C. and a refractive index of 1.50 to 1.57 at 30.degree. C., which is formed by mixing (a) 20 to 90% by weight of an allyl ester oligomer, (b) 10 to 80% by weight of at least one polyvalent allyl ester monomer selected from the group consisting of diallyl phthalate, diallyl isophthalate, diallyl terephthalate, diallyl adipate, triallyl (iso)cyanurate and triallyl trimellitate, and (c) up to 40% by weight of at least one monofunctional polymerizable monomer selected from the group consisting of vinyl benzoate, allyl benzoate, phenyl (meth)acrylate and benzyl (meth)acrylate.

Abstract: Crosslinked polymeric microparticles obtained by polymerization of a mixture of polymerizable ethylenically unsaturated monomers being substantially free of monomers containing polar groups are disclosed. At least one of said monomers is a polyethylenically unsaturated crosslinking monomer free of oxyethylene groups and is present in amounts of 10 to 90 percent by weight based on total weight of said polymerizable ethylenically unsaturated monomers. The crosslinked polymeric microparticles are prepared by aqueous emulsion polymerization techniques in the absence of polyester emulsifier. The microparticles are separated from the aqueous polymerization medium and converted into organic medium by azeotropic distillation. The microparticles are useful in organic solvent-based high solids coating compositions and can be used in color coats, clear coats or composite color-clear coatings where the crosslinked polymeric microparticles can be contained in the color coat and/or in the clear coat.

Abstract: A process for producing a vinyl chloride polymer for matted moldings which comprises performing the suspension polymerization of vinyl chloride monomer or a mixture of vinyl monomers composed mainly of vinyl chloride in an aqueous medium, in the presence of (A) 0.01 to 3 parts by weight of a polyfunctional monomer having two or more ethylenic double bonds in the molecule and (B) 0.00005 to 0.01 part by weight of antioxidant, thereby yielding a vinyl chloride resin composed of 5 to 90% by weight of tetrahydrofuran-insoluble gel fraction, with the remainder being tetrahydrofuran-solubles.

Abstract: The present invention discloses an optical material having excellent transparency, impact resistance and heat resistance and having a low specific gravity and a high refractive index comprising a resin obtained by radical polymerization of specific difunctional (meth)acrylate (A) and aromatic vinyl monomer (B) and, if necessary, polymerizable monomer (C) copolymerizable with the ingredients (A), or (B) or by radical polymerization of the ingredients (A), (B) and (C) under the presence of a radical polymerizable or not-radical polymerizable compound having alkoxysilyl group, epoxy group, alcoholic hydroxy group or carboxyl group in the molecule, an optical molding product comprising the optical material, as well as production process therefor. The optical molding product is utilized as for ophthalmic lenses or lenses for various kinds of optical equipments, prisms, optical fibers, optical waveguides and optical discs.

Abstract: A process for producing a vinyl chloride polymer for matted moldings which comprises performing the suspension polymerization of vinyl chloride monomer or a mixture of vinyl monomers composed mainly of vinyl chloride in an aqueous medium, said suspension polymerization being performed after the addition of an aqueous dispersion obtained by dispersing a polyfunctional monomer having 2 or more ethylenic double bonds in the molecule into an aqueous solution of a water-soluble partially saponified polyvinyl alcohol, a water-soluble cellulose eter or an emulsifier, thereby yielding a vinyl chloride resin composed of 5 to 90 wt % tetrahydrofuran-insoluble gel fraction, with the remainder being tetrahydrofuran-solubles.

Abstract: The plastic lens of the present invention consists of a copolymer obtained by copolymerizing a monomer mixture consisting of given proportions of diethylene glycol bis(allyl carbonate), benzyl methacrylate, diallyl phthalate (these three monomers has been used as a monomer mixture for conventional plastic lenses) and, as an additional monomer, an alkyl methacrylate. This copolymer has excellent adhesion to upper and lower molds and, when immersed in, for example, a cleaning solution such as a methylene chloride-strong alkali mixed cleaning solution or the like, causes no separation from the molds; accordingly in the copolymer, there can be prevented the occurrence of surface roughening, cloudiness and striae which have been problems in conventional plastic lenses.

Abstract: A plastic light conduit of cross-linked polymer material having good light transmitting characteristics, without voids or noticeable bubbles, is disclosed. Also disclosed is a method of manufacture and an apparatus, involving progressive heating of reactive monomer mixture in a tube which is submerged in a progressive reactor utilizing cold oil to maintain a cold, non-reacting zone, and hot water to create a hot zone that causes reaction, while simultaneously carrying away the excess exothermic heat of reaction.

Abstract: Resin compositions for laminated sheets and laminated sheets produced therefrom are disclosed, the compositions comprising at least one allyl ester resin composed of a polybasic acid and a polyhydric alcohol, wherein an allyl ester group of said resin is bonded to at least one of terminals thereof.

Abstract: A diallyl aromatic dicarboxylate derivative of the formula ##STR1## wherein Y is hydrogen atom or perfluoroalkenyl group having 6 to 14 carbon atoms, is a novel compound. The compound (1) is a starting material for a prepolymer containing a repeating unit derived from diallyl aromatic fluorine-containing dicarboxylate and represented by the formula ##STR2## wherein X is prefluoroalkenyl group having 6 to 14 carbon atoms.

Abstract: Novel organic glass with a high refractive index comprising a copolymer of (a) a diallyl isophthalate monomer, (b) an allyl or methallyl benzoate monomer and (c) a diester of maleic acid and/or diester of fumaric acid monomer, which also shows excellent light resistance and excellent other physical properties such as excellent moldability, high impact resistance, high dimension stability, excellent mechanical processing properties, excellent dyeability and excellent hard coating property, and is useful as a material for optical or optoelectronic parts such as lenses, prisms, reflecting mirror and window materials.

Abstract: Disclosed are a coating composition (A) for preventing adhesion of organisms which comprises as its vehicle component a homopolymer or a copolymer, the homopolymer being one prepared by homopolymerizing a phenol-modified unsaturated monomer obtained by reacting (a) an unsaturated monomer containing epoxy group and/or hydroxyl group with (b) an addition reaction product of a phenolic compound with a compound having one carboxylic anhydride group per molecule, and the copolymer being one prepared by copolymerizing said phenol-modified unsaturated monomer and a radically polymerizable unsaturated monomer, and also a coating composition (B) for preventing adhesion of organisms which comprises as its vehicle component a phenol-modified resin prepared by reacting (c) a resin containing epoxy group and/or hydroxyl group with (b) and addition reaction product of a phenolic compound with a compound having one carboxylic anhyhdride group per molecule.

Abstract: A diallyl terephthalate prepolymer consisting essentially of diallyl terephthalate monomer units, having(a) 10 or less of the monomer units in the carbon-carbon bonded molecular chain portion which is composed of the allyl groups of the monomer units, and either(b) an unsaturation in a range of from 40 to 70, as represented by an iodine value determined by the Wijs method,(c) a number-average molecular weight in a range of from 6,000 to 10,000 as polystyrene, and a weight-average molecular weight in a range of from 10,000 to 70,000 as polystyrene, both being determined by gel permeation chromatography, and(d) a melt viscosity in a range of from 30,000 to 90,000 CP at 170.degree. C.

Abstract: A process for synthesizing ethers of alkyl alpha-(hydroxymethyl)-acrylate by reacting alkyl acrylate and formaldehyde in the presence of a DABCO catalyst. The ethers may be used as cross-linking agents for thermoplastic polymers. Further, these ethers in turn enable synthesis of cyclopolymers that may show promising biological activity.

Abstract: Disclosed are a coating composition (A) for preventing adhesion of organisms which comprises as its vehicle component a homopolymer or a copolymer, the homopolymer being one prepared by homopolymerizing a phenol-modified unsaturated monomer obtained by reacting (a) an unsaturated monomer containing epoxy group and/or hydroxyl group with (b) an addition reaction product of a phenolic compound with a compound having one carboxylic anhydride group per molecule, and the copolymer being one prepared by copolymerizing said phenol-modified unsaturated monomer and a radically polymerizable unsaturated monomer, and also a coating composition (B) for preventing adhesion of organisms which comprises as its vehicle component a phenol-modified resin prepared by reacting (c) a resin containing epoxy group and/or hydroxyl group with (b) an addition reaction product of a phenolic compound with a compound having one carboxylic anhydride group per molecule.

Abstract: Novel organic glass comprising a copolymer of (a) a diallyl phthalate monomer, (b) an allyl benzoate monomer and (c) a glycol bis(allylcarbonate) monomer, which has a high refractive index and excellent other physical properties such as high impact resistance, high dimension stability, excellent mechanical processing properties, excellent dyeability, excellent hard coating property, and is useful as a material for optical parts such as lenses and prisms.

Abstract: This invention relates to a process for polymerizing an aqueous solution of an .alpha.,.beta.-ethylenically unsaturated monomer and at least one crosslinking monomer to produce a water-swellable polymer using sodium thiosulfate as a component of a redox initiator system. The use of sodium thiosulfate as a component of a redox initiator system for the polymerization allows for controlling the rate of initiation so as to increase the time required for gel formation during polymerization. The resulting hydrated polymer of the present invention breaks up more uniformly and with greater ease resulting in a higher per batch yield.

Abstract: A novel heat-curable acrylic-terminated monomer is provided which exhibits an optically anisotropic melt phase at a temperature which enables it to undergo melt processing in the formation of molded articles, etc. Subsequent to melt processing articles prepared from the monomer are capable of being cured to produce a thermoset self-reinforced composite which is soft and flexible relative to prior art monomers. The monomer may, for example, consist essentially of the reaction product of a methacrylic-substituted phenol and terephthalic acid.

Abstract: (Methy)acrylic acid esters of the general formula(Mo).sub.n --[--A--O--CO--CH.sub.2 --O--CH.sub.2 --CH.sub.2 --O--CH.sub.2 --CO--O--].sub.x --A--(OM).sub.nare described whereinA is an alcohol radical having at least 4 chain atoms between two junction sites.M is CH.sub.2 .dbd.C(R.sup.1)--CO wherein R.sup.1 stands for hydrogen or methyl,n is 1 or 2, andx is 0.3 to 3.These esters are suited for the preparation of dental compositions.

Abstract: Ethylenically unsaturated monomers containing activated ester groups are used to make polymers and copolymers which are useful in coatings, adhesives and moldings.

Abstract: A plastic lens having a refractive index of not less than 1.55, comprising a polymer formed from dimethallyl phthalate as major monomeric constituent and, if necessary, one or more monomers represented by the general formula ##STR1## wherein R.sub.1 and R.sub.2 represent each a hydrogen atom or methyl group and m and n represent each an integer of from 0 to 3, or ##STR2## wherein R.sub.3 and R.sub.4 represent each a hydrogen atom or methyl group and n represents an integer of from 2 to 9. A method for manufacturing such a lens is also disclosed.

Abstract: A plastic lens which comprises a polymer (A) containing as major component at least one radicalpolymerizable biphenyl compound represented by the general formula [I]: ##STR1## wherein each of R's represents a hydrogen atom or methyl group, has a high refractive index of not less than 1.55 and is excellent in transparency, processability, impact resistance, and dyeability.

Abstract: Organic glass having a high refractive index and excellent other physical properties and being suitable as materials for optical parts such as lenses and prisms. The organic glass comprises a copolymer obtained by adding a polymerization initiator to a mixture of three monomer components of diallyl isophthalate, a benzoate ester with an unsaturated alcohol, and a methacrylate ester and then polymerizing the mixture.

Abstract: Novel heat-curable acetylene-terminated monomers are provided which exhibit an optically anisotropic melt phase at a temperature which enables it to undergo melt processing in the formation of molded articles, etc. The monomers are capable of being heat-cured at temperatures in excess of the melt processing temperatures to produce a thermoset self-reinforced composite.

Abstract: A polymer capable of forming an anisotropic melt characterized in that the polymer chain includes residues of cross-linking reactants at a concentration sufficient to give a polymer with a melt viscosity of not greater than 10.sup.7 Nsec/m.sup.2 measured by capillary rheometry at a shear rate of 10.sup.4 N/m.sup.2. The polymers exhibit favorable shear dependent viscosity characteristics in that the viscosity is high under low shear conditions and is low under high shear conditions, as judged by the viscosity characteristics of polymers of the same composition but not containing the residues of cross-linking reactants.

Abstract: 4-Vinyl-2-methylenebutanedioic acid and its esters, as well as amide and nitrile analogs of these compounds, are disclosed. These compounds are capable of undergoing a rapid free radical cyclopolymerization reaction. The compounds, themselves, may be used as film-formers (for example, in paints or plastics) or may be used as groups pendant from a backbone, especially a low molecular weight backbone, to form other, more complex film-forming polymer precursor materials.

Abstract: A lens having a high refractive index with a low dispersion produced by copolymerizing a polyfunctional allyl monomer with at least one monomer selected from the group represented by the general formula A: ##STR1## X: H, CH.sub.3, Cl Y: H, CH.sub.3, C.sub.2 H.sub.5, n-C.sub.3 H.sub.7, iso-C.sub.3 H.sub.7, OCH.sub.3, C.sub.6 H.sub.11, Cl, Br, CH.sub.2 Cl, CH.sub.2 Br, C.sub.6 H.sub.5, CH.sub.2 C.sub.6 H.sub.5, SCH.sub.3m=0, 1, 2n=0, 1, 2, 3, 4, 5.This lens is excellent in its transmittance, pencil hardness, impact resistance, dyeability, coating adhesion, solvent resistance, workability, etc.

Abstract: A molding compound is disclosed comprising a diallyl phthalate compound and capsules of water.

Abstract: A process is described for making sterically stabilized non-aqueous dispersions of polymer microparticles, in which (1) monomers including at least one crosslinking monomer are polymerized in an aqueous medium at a temperature at least 10.degree. higher than the glass transition temperature of the polymer to be formed, in the presence of a block or graft copolymer stabilizing agent containing in the molecule, as the component solvated by the aqueous medium, a polymer chain derived from a polyethylene glycol of molecular weight at least 1000, under conditions such that there is at no time present a separate monomer phase and (2) the microparticles thus obtained are transferred into a non-aqueous medium which is capable of dissolving the polyethylene glycol in question, when the latter is in the non-hydrated state, to the extent of at least 10% by weight at room temperature.