Abstract: A thermoplastic resin composition is prepared by blending 50-95 wt. % of a copolymer (A) of 10-75 wt. % of .alpha.-methyl styrene, 10-60 wt. % of methyl methacrylate, 5-35 wt. % of acrylonitrile and 0-20 wt. % of a monomer copolymerizable therewith; and 5-50 wt. % of a graft copolymer (B) comprising 50-85 wt. parts of a butadiene-based rubber polymer and 15-50 wt. parts of a vinyl monomer graft-polymerized onto the rubber polymer. The butadiene-based rubber polymer includes 50-98 wt. % of butadiene, 2-50 wt. % of an aromatic polycyclic vinyl monomer represented by a formula (I) below and 0-20 wt. % of a monomer copolymerizable therewith: ##STR1## wherein R denotes an optionally substituted biphenylyl or naphthyl group, and R.sub.1 denotes a hydrogen atom or a methyl group.

Abstract: The present invention relates to a core-shell polymer which is useful for polyoxymethylene resin, a polyoxymethylene resin composition containing the core-shell polymer and a molded article made of the polyoxymethylene resin.The core-shell polymer is produced by an emulsion polymerization reaction using an oligomeric surfactant and a neutral radicals-liberating polymerization initiator.This core-shell polymer makes the molded article be improved on the impact strength, elongation at the weld line, weatherability, thermal stability, etc., and the molded articles is used as various products.

Abstract: A modified block copolymer composition comprising a thermoplastic polymer and a modified block copolymer consisting essentially of a base block copolymer of a monovinyl substituted aromatic hydrocarbon polymer block and an olefin compound polymer block having an ethylenic unsaturation degree not exceeding 20%, the base block copolymer having a molecular unit containing a carboxylic acid group and/or a group derived therefrom grafted thereto. The modified block copolymer composition of the present invention is a resinous composition excellent in impact resistance, adhesion, paint adhesion, weatherability, resistance to thermal deterioration, transparency and gloss or a rubbery or leather-like composition excellent in heat resistance, adrasion resistance, compression set resistance, adhesion, transparency, oil resistance, weatherability and resistance to heat aging.

Abstract: A polymer composition comprising2-50 parts by weight of a fine particles component dispersed in a matrix described later, of (1) a high-nitrile (co)polymer, wherein the proportion of the nitrile polymeric unit (a) is at least 86% by weight based on the total of the high-nitrile (co)polymer, and98-50 parts by weight of a matrix of (2) a low-nitrile copolymer comprising the nitrile polymeric unit (a), the acrylic ester polymeric unit (b) and the aryl vinyl polymeric unit (c), wherein the proportion of the polymeric unit (a) is 50-85 % by weight and the polymeric unit (b) and the polymeric unit (c) occupy the remaining portion.

Abstract: Compounds of Formula I ##STR1## wherein Z is an aromatic group, each R is individually selected from the group consisting of alkyl groups of from 1 to about 12 carbon atoms, thioalkyl groups of from 1 to about 12 carbon atoms, and halogen atoms, n is from 1 to about 6, and x is from 0 to 7, are suitable for use in preparing rubber latex particles. The rubbers are useful as substrates in graft copolymers and the resulting graft copolymers are suitable for use in thermoplastic blend compositions, particularly with transparent polymers. The rubber materials are advantageous in that they exhibit low glass transition temperatures and high refractive indices.

Abstract: Polymers comprising blocks of a hydrogenated conjugated diene (B), a vinylarene (A), and an alkyl methacrylate (M), are readily prepared as a mixture of molecules having the structures B-A-M and B-A-M-A-B wherein both structures are effective as viscosity index improvers for oil compositions. Reaction of the polymers with a primary or secondary amine results in a dispersant viscosity index improver.

Abstract: Multi-stage rubber-based MBS resin compositions are provided which include a polymeric substrate stage of a conjugated diolefin-based polymer or copolymer and optional units derived from a cross-linking agent or agents, and at least one polymeric graft stage graft polymerized in the presence of the substrate stage which include monomers of an acrylate, a vinyl aromatic, or a mixture of those monomers and optional units derived from a cross-linking agent or agents and/or units which serve as a graft-linking agent or agents wherein the weight ratio of acrylate in all graft stages combined to vinyl aromatic in all graft stages combined is at least 1.2:1. Additionally, modified vinyl chloride polymer compositions which include a vinyl chloride polymer or copolymer in combination with an impact modifying, yellowness index improving amount of the multi-stage rubber-based resin compositions above are provided.

Abstract: Improved plasticizer resistant pressure sensitive hot melt adhesive compositions are prepared by incorporating in the adhesive polymer, tackifying resin and oil 5 to 70% by weight of the adhesive of a core shell modifier comprising a crosslinked rubbery core and a glassy thermoplastic polymer shell, the core being crosslinked by the presence therein of up to 5% by weight of a polyunsaturated monomer having two or more non-conjugated sites of unsaturation of unequal reactivity.

Abstract: A resin composition comprising a graft copolymer of a rubbery polymer having a vinyl cyanide compound and an aromatic vinyl compound grafted thereon, and a copolymer comprising a vinyl cyanide compound and an aromatic vinyl compound. A molded article of the resin composition is characterized with improved coating performances.

Abstract: Disclosed is a process for producing a styrene polymer composition, which comprises polymerizing styrene monomer using a catalyst comprising (A) aluminoxane and (B) a compound of the group IV B transition metal in the periodic table, in the presence of rubber-like elastomer.The resin composition obtained thereby is superior in heat resistance, and impact strength, and utilized as the starting material for various moldings.

Abstract: An improved process for the preparation of segmented copolymers of polyolefins and poly(methacrylates) is disclosed.

Abstract: Disclosed is a process for the production of a rubber-reinforced polymer composition having a bimodal particle size distribution using parallel, substantially plug flow reactors to separately polymerize the same or different solutions of a rubber in a monovinylidene aromatic monomer and optionally at least one other monomer. After separate partial polymerizations, first and second prepolymer compositions are produced containing rubber particles having average particle sizes of from 0.05 to 1.5 micrometer and from 0.7 to 10 micrometer, respectively, with the average rubber particle size of the second prepolymer composition being at least 1.3 times the average rubber particle size of the first prepolymer composition.

Abstract: A crosslinked, unsaturated elastomeric polymer of a C.sub.4 to C.sub.7 isomonoolefin and a C.sub.4 to C.sub.14 conjugated multiolefin is produced by curing the corresponding uncrosslinked polymer having a low level of chemically bound halogen with a curing agent which reacts only with the halogen (e.g., zinc oxide) in combination with a bifunctional dienophile (e.g., a bismaleimide). The uncrosslinked elastomeric polymer is particularly suitable for use in the pharmaceutical industry, for example, for container closures. Shaped rubbery products comprising the crosslinked copolymer are also provided.

Abstract: Disclosed is an improved process of the post-emulsion method capable of forming crosslinked resin particles which do not have fusion bonds between particles and which have good storage stability and good redispersibility in an aqueous medium. The process comprises (a) dispersing in an aqueous medium a resinous component comprising (I) a base resin having a glass transition temperature (Tg) of 0.degree. C. or less and a polymerizable double bond, (II) a monomer which, when polymerized, provides a resin of which Tg is 20.degree. C. higher than that of said base resin, or a resin of which Tg is 20.degree. C. higher than that of the base resin, and (III) a polyvinyl compound; (b) crosslinking inside the dispersed resin particles and; (c) removing the aqueous medium therefrom.

Abstract: Modified rubber compositions comprise by weight about 15-60% of a highly saturated aliphatic rubber such as ethylene-propylene-diene rubber, about 25-80% of acrylate monomer units; and less than about 5% multi-functional monomer units. The compositions exist as amorphous heterogeneously dispersed phases. The first phase comprises the copolymer rubber to which polymers of at least 10% of the other monomer units are grafted. The second phase comprises the other monomers polymerized as homo and copolymers, not grafted to the rubber. Optionally, up to 20% of the composition comprises high index monomer units. The high index monomer units may be copolymerized with the acrylate and grafted to the rubber. Greater than 10% of the monomer units other than rubber are grafted to the rubber. The number average molecular weight of the grafts is between 10,000 and 80,000 daltons.

Abstract: This invention relates to poly(vinyl chloride) injection molding compositions which contain novel additive polymers which modify the rheology characteristics of the composition, and to the novel additive polymers themselves.

Abstract: A graft copolymer is formed by graft-polymerizing 10-95 wt. parts of a vinyl monomer onto 5-90 wt. parts of the rubber polymer which comprises 40-99 wt. % of butadiene and 1-60 wt. % of an aromatic polycyclic vinyl monomer represented by the following formula (I) or (II): ##STR1## wherein R denotes a hydrogen atom or a methyl group. The graft copolymer is characterized by the rubber polymer having a high refractive index as well as a low glass transition temperature due to the use of the aromatic polycyclic vinyl monomer. Accordingly, the graft copolymer per se may be used as a thermoplastic resin having good transparency and impact resistance at a low rubber polymer content and may also be added to a transparent thermoplastic resin inclusive of a vinyl chloride resin and a styrene-acrylonitrile copolymer resin to provide the thermoplastic resin with an improved impact resistance while retaining a good transparency.

Abstract: A hydrogenated diene block copolymer having a polystyrene-reduced number-average molecular weight of 50,000-600,000 which is a hydrogenation product of an (A)--(B) block copolymer in which (A) means an alkenyl aromatic compound polymer block and (B) means a conjugated diene homopolymer block wherein the vinyl content of the conjugated diene portion is more than 60%, or an alkenyl aromatic compound-conjugated diene random copolymer block wherein the vinyl content of the conjugated diene portion is 15% or more, an (A)--(B)--(C) block copolymer in which (A) and (B) are as defined above and (C) means an alkenyl aromatic compound-conjugated diene copolymer tapered block wherein the proportion of the alkenyl aromatic compound increases gradually, or an (A)--(B)--(A) block copolymer in which (A) and (B) are as defined above, in which block copolymer(1) the weight proportion of theh alkenyl aromatic compound/the conjugated diene is 5/95 to 60/40, and(2) the content of the bound alkenyl aromatic compound in at least o

Abstract: The present invention relates to rubber-modified styrene copolymer that exhibits excellent rigidity, impact strength, external appearance and fluidity, while retaining rigidity, impact properties and external appearance, and when prepared by copolymerizing a maleimide monomer, has high heat resistance and therefore is suitable for materials for components of electric equipments, electronic equipments, automobiles and business machines.

Abstract: A bituminous composition comprising a bituminous component and a polymer which comprises at least one block of a conjugated diolefin and at least one block of an alkyl methacrylate.

Abstract: A modified polymer rubber is obtained by(1) graft-polymerizing at least one grafting monomer to a shreaded rubbery polymer (A) in an aqueous suspension at a temperature of 30.degree.-130.degree. C. to obtain a graft polymer, and(2) kneading the graft polymer with at least one polymerizable monomer in the presence of a free radical initiator at a temperature of 180.degree.-280.degree. C. This process does not cause gel formation and is advantageous in manufacturing cost.The modified polymer rubber thus obtained is excellent in processability and storage stability, and highly useful as a compatibilizer for various resins.

Abstract: A polymer particle is provided comprising a rubbery polymer and a methacrylic glassy polymer as formed in latex interpenetrating polymer networks structure, which is prepared by swelling a rubbery polymer with a swelling solvent and carrying out an emulsion polymerization reaction of methacrylic monomers in the presence of said swollen rubbery polymer. Also provided are a resin composition comprising the polymer particles, such as poly (alkylene terephthate) resin melt-blended with the polymer particles, and a molded article of the resin composition. The molded article has a high impact-strength.

Abstract: This invention relates to a core-shell polymer which is useful for polyoxymethylene resin, a polyoxymethylene resin composition containing the core-shell polymer and a molded article made of the polyoxymethylene resin composition.The core-shell polymer comprises a rubbery polymer core and a glassy polymer shell and has substantially no detectable anion.This core-shell polymer makes the molded articles be improved on the impact strength, elongation at the weld line, etc. The molded articles is used as various products (such as gears, reels, etc.).

Abstract: Disclosed is a dental composition comprising a (meth)acrylic ester compound as the principal component and containing a polymerization initiator, which is characterized by having incorporated therein a grafted rubber obtained by polymerizing at least one ethylenically unsaturated monomer in the presence of a rubber. This dental composition can be cured to yield a cured product having excellent strength properties and, therefore, is particularly useful in applications such as a molar restoration material and a denture base resin.

Abstract: The invention relates to graft-modified linear polyethylene with low density (<940 kg/dm.sup.3) (LLDPE), and in particular with very low density (density <915 kg/dm.sup.3) (VLDPE), grafted particularly with styrene/maleic anhydride.These polyethylenes are very good impact modifiers with a high UV resistance and a high degree of toughness and do not cause discoloration of the polyamides and polyesters modified with them. They can be prepared in a simple and economically efficient manner with a high degree of conversion.These polyethylenes are also highly suited as impact modifiers, adhesives or adhesive layers, heat-seal layers, bonding layers in composite films, compatibility enhancement agents as well as bonding promotors, or as components of such agents or layers.Graft-modified polyethylene can be prepared by converting a linear low-density polyethylene with the grafting material at at temperature higher than 110.degree. C.

Abstract: An impact modifier obtained by emulsion polymerizing acrylic monomer(s), etc., in the presence of a conjugated diene rubber to give a graft rubber polymer, or obtained by polymerizing acrylic monomer(s) and the like ethylenically unsaturated monomers in the presence of the graft rubber polymer, is effective for improving impact resistance and weathering resistance of molded articles obtained from thermoplastic resin compositions containing such an impact modifier.

Abstract: Disclosed is a methacrylic resin cast plate which is comprised of 100 parts by weight of [I] polymethyl methacrylate or a methyl methacrylate copolymer containing at least 90% by weight of methyl methacrylate units and, dispersed therein, a graft copolymer [IV] obtained by graft-polymerizing a hard resin component [III] containing at least 90% by weight of methyl methacrylate units onto a crosslinked rubbery copolymer [II] containing at least 45% by weight of butyl acrylate units and having an average particle diameter of 0.1 to 1 .mu.m, the amount of the graft copolymer [IV] being 2 to 30 parts by weight as the amount of the crosslinked rubbery copolymer.

Abstract: Novel diene/methacrylate ester block polymers, especially tertiary butyl methacrylate ester block polymers are uniquely prepared at near ambient temperatures and capable of being hydrolyzed and neutralized to yield the corresponding methacrylic acid and methacrylic acid salt (ionomer) derivatives. The compositions are usefully employed in the preparation of thermoplastic elastomers, adhesives and laminating films.

Abstract: Disclosed herein is a continuous mass polymerization process for the preparation of acrylonitrile-butadiene-styrene-ester polymers (ABSE) having a balance of gloss, tensile strength, impact strength, processability and heat resistance properties.

Abstract: Copolymers of styrene or a-methylstyrene and at least one comonomer, containing crosslinked elastomer particles, can be light-stabilized by modifying the elastomer particles by copolymerization with a suitable derivative of a sterically hindered amine. The modification is preferably carried out by graft polymerization, the elastomer used preferably being polybutadiene.

Abstract: An improved method for carboxylating styrenic resins and particularly impact-modified styrenic resins such as ABS resins, by melt-processing a mixture comprising the styrenic resin, an ethylenically-unsaturated carboxylic compound, and, optionally, a free-radical generator.

Abstract: The invention relates to a graft copolymer obtainable by reacting a rubbery base polymer, which has been provided with hydroperoxide groups via photo-oxidation, with one or more radical-polymerizable graft monomers, the graft copolymer being based upon 90-20 parts of a rubbery base polymer containing at least 4 (four) hydroperoxide groups per rubber chain and 80-10 parts of one or more of the graft monomers.

Abstract: An improved method for carboxylating styrenic resins and particularly impact-modified styrenic resins such as ABS resins, by melt-processing a mixture comprising the styrenic resin, an ethylenically-unsaturated carboxylic compound, and, optionally, a free-radical generator.

Abstract: Disclosed is a graft copolymer resin prepared by graft polymerizing a vinyl compound onto a composite-structured acrylic rubber whose particles are composed of a core consisting of a diene rubber enlarged by treatment with an acid group-containing copolymer latex, and an outer layer consisting of an acrylate polymer having a crosslinked structure formed by the combined use of a graft-linking agent and a cross-linking agent. This graft copolymer resin may be blended with a rigid thermoplastic resin in a specific proportion. This resin composition imparts a good gloss to the molded articles formed therefrom, while retaining excellent impact resistance and weather resistance.

Abstract: A method of producing a modified polypropylene comprising the step of graft-polymerizing a propylene random copolymer containing an unconjugated diene comonomer represented by the general formula: ##STR1## wherein R.sub.1 -R.sub.4 are H or an alkyl group having 1-6 carbon atoms, and n is an integer of 1-20, with a monomer having an unsaturated bond by a radical method.

Abstract: A core/shell polymer is capable of increasing a composition's whiteness of opacity. The shell polymer has either a crystalline structure of a T.sub.g of at least about 50.degree. C. The shell polymer comprises (i) at least one nonionic monomer selected from the group consisting of soft alkyl acrylate monomers, soft methacrylate ester monomers, and mixtures thereof, and (ii) at least one additional nonionic monomer. The core has a different composition than the composition of the shell and a T.sub.g of at least about 50.degree. C. The core comprises alkenyl aromatic monomers. The core and shell polymers are homopolymers or copolymers.

Abstract: Disclosed is a modifier to be incorporated in a polyvinyl chloride resin, which is a graft copolymer obtained by carrying out, in the presence of 100 parts by weight of a butadiene rubber having a swelling degree of 10 to 50 and an average particle diameter of 0.1 to 0.4 .mu.m, first-stage graft polymerization of 1 of 42 parts by weight of methyl methacrylate and 0 to 5 parts by weight of an alkyl acrylate, second-stage graft polymerziation of 10 to 120 parts by weight of styrene and third-stage graft polymerization of 7 to 75 parts by weight to methyl methacrylate and 0 to 20 parts by weight of an alkyl acrylate, the content of the butadiene rubber in the graft copolymer being 35 to 75% by weight. The polyvinyl chloride resin composition having this modifier incorporated therein provides a molded article having excellent impact resistance, solvent resistance, and transparency.

Abstract: An impact resistance modifier for polycarbonate, which is a copolymer, comprising an elastomer and a methyl methacrylate copolymer, which are bonded covalently. The methyl methacrylate copolymer is one that is compatible by itself with polycarbonate resin due to specific comonomers. Such comonomers are aromatic (meth)acrylic esters and (meth)acrylamides, cycloalkyl(meth)acrylamides and cycloalkylmaleimides. Thermoplastic molding compounds comprising polycarbonate and the new impact resistance modifier exhibit excellent impact resistance.

Abstract: A photosensitive elastomeric composition comprising (1) at least one elastomer, (2) an addition-polymerizable compound having at least one CH.sub.2 .dbd.C< group and (3) a polymerization initiator activatable by actinic light, wherein the elastomer (1) is an elastomer selected from (a) an elastomeric polymer composed of a polyene monomer containing at least two non-conjugated double bonds and a conjugated diene-type monomer or both a conjugated diene-type monomer and a copolymerizable vinyl monomer and (b) an elastomeric linear A-B type (wherein A represents a polymer block of a monovinyl aromatic compound and B represents a polymer block of a conjugated diene-type monomer) block copolymer in which a terminal group having a polymerizable ethylenic double bond is present in at least one end of the molecular chain.

Abstract: A process for producing a block copolymer composed of polyphenylene sulfide segments and polyphenylene sulfide sulfone segments comprises reacting a polyphenylene sulfide prepolymer with a mixture of a dihalodiphenyl sulfone and a sulfidization agent, or a polyphenylene sulfide sulfone prepolymer with a mixture of a polyhalogenated aromatic compound and a sulfidization agent.

Abstract: The improvement of toughness and impact strength of polyester resins is achieved by blending 60-90 parts by weight of the polyester with 10-40 parts by weight of an ethylene, propylene, diene rubber, having 2-20 unsaturated C.dbd.C linkages per 1000 carbon atoms and which has been grafted with glycidyl methacrylate to a level of 1-10 percent by weight.

Abstract: The pressure-sensitive adhesive of the invention comprises a latex of natural rubber graft-copolymerized with 2 to 10% by weight of styrene and 10 to 25% by weight of methyl methacrylate and a finely divided particulate material having no thermoplasticity such as silica gels and zeolites in an amount of 5 to 30 parts by weight per 100 parts by weight of the natural rubber. The pressure-sensitive adhesive has excellent characteristics in the adhesive bonding, resistance against blocking, frictional behavior, heat resistance and abrasion resistance and also is free from the trouble of decrease in the adhesive bonding strength caused by the transfer of a silicone oil from the roller of printing machines.

Abstract: Core/shell polymers containing a rubber-core and a thermoplastic shell acrylate-vinylacetate-acrylic terpolymer having excellent cold seal strength properties.

Abstract: Process for the preparation of a thermoplastic moulding composition of 10 to 65% by weight of at least one graft polymer which is obtainable by emulsion polymerization of styrene and acrylonitrile in a weight ratio of 90:10 to 50:50, it being possible for all or some of the styrene to be replaced by .alpha.-methylstyrene or methyl methacrylate, in the presence of at least one rubber base, and the weight ratio of monomers employed to rubber polymer employed being 20:80 to 70:30, and 90 to 35% by weight of a copolymer of styrene and acrylonitrile in a weight ratio of 90:10 to 50:50, it being possible for all or some of the styrene to be replaced by .alpha.-methylstyrene or methyl methacrylate, wherein, to prepare the graft polymer, the grafting monomers and 0.05 to 1.00 part by weight (per 100 parts by weight of grafting monomer) of a mercaptan are added stepwise to the latex of the rubber base over a period of time, the part amount of the monomer added in each time interval .DELTA.t.sub.n+1 being 0.30 to 0.

Abstract: A resin having a low dielectric constant obtained by heat-curing 100 parts by weight of a butadiene polymer containing in its polymer chain at least 50 mol% of a 1,2-butadiene unit having a double bond in its side chain and from 10 to 100 parts by weight of a vinyl compound having at least 3 vinyl groups in one molecule in the presence of an organic peroxide. Also disclosed is a resin having flame resistance obtained by heat-curing a blend of an organic peroxide with a composition comprising 100 parts by weight of a butadiene polymer containing in its polymer chain at least 50 mol% of a 1,2-butadiene unit having a double bond in its side chain, from 10 to 100 parts by weight of a vinyl compound having at least 3 vinyl groups in one molecule and at least one member selected from the compounds of the formulas I-IV: ##STR1## wherein X is H or CH.sub.3, Y is Br or Cl, A is --, --o--, --CO--, SO.sub.2, --CH.dbd.CH--, --C(CH.sub.3).sub.2 --or --(CH.sub.2 .sub.

Abstract: Hydroperoxidized rubber-containing polymers are prepared in a process wherein a rigid phase polymer is prepared by polymerization of one or more free radically polymerizable monomers in the presence of a hydroperoxidized rubbery intermediate in a well stirred back-mixed reactor operating under essentially homogeneous conditions at a solids content of from about 30 to about 75 percent by weight, and an initial rubber content in the feed of from about 5 to about 12 percent by weight.

Abstract: The invention relates to a process for the production of graft polymers of resin-forming monomers on a rubber in which a very high graft yield is obtained by the use of an initiator system of an organic hydroperoxie and ascorbic acid. The graft polymers obtained are suitable as thermoplastic molding compositions or as constituents thereof.

Abstract: Stable dispersion of addition (co)polymers in an inert relatively non-polar organic hydrocarbon liquid, the dispersed particles embracing both a (co)polymer and a polymer containing an ethylenically unsaturated monomer. The (co)polymers are substantially composed of:(a) 5 to 100 mole % of styrene and/or methyl styrene;(b) 0 to 95 mole % of alkyl methacrylate having 1 or 2 carbon atoms in the alkyl group and/or alkoxyalkylene methacrylate having 1 or 2 carbon atoms in the alkoxy group and the alkylene group;(c) 0 to 40 mole % of alkyl methacrylate having 3 to 12 carbon atoms in the alkyl group;(d) 0 to 40 mole % of hydroxalkyl methacrylate having 2 to 12 carbon atoms in the alkyl group and/or glycidyl methacrylate; and(e) 0 to 20 mole % of m methacrylic acid.The (co)polymers are grafted to a polymer of a number average molecular weight of 2000 to 10.

Abstract: Dense star polymers on immobilized cores are very useful as ion-exchange resins and chelation resins. For example, an aminated form of chloromethylated styrene/divinyl benzene copolymer can be employed as an immobilized core compound and reacted successively with methyl acrylate via a Michael addition reaction and then with ethylenediamine to form a first generation dense star polymer or dendrimer. These reactions can then be repeated to form second and third generation dendrimers.

Abstract: In the suspension polymerization of styrene monomers in water using suitable suspension stabilizers, the only modifier needed has been found to be organotin compounds in amounts from 10 to 1000 ppm based on monomer. The product beads have a narrow bead size distribution.