Patent ID: 7294399

Claim:
A thermoplastic composition comprised of a. about 40-90 weight percent of a rigid thermoplastic copolymer matrix consisting of 50-85 weight percent methyl methacrylate, and 15-50 weight percent of an alkyl acrylate selected from the group consisting of ethyl acrylate, methyl acrylate, and mixtures thereof; and b. about 10-60 weight percent of a multi-stage, sequentially-produced polymer characterized by: (A) a first stage which is optionally non-elastomeric, relatively hard, and has a glass transition temperature of greater than 25° C., and which is polymerized from a monomer mixture consisting of 50-85 weight percent of methyl methacrylate, and 15-50 weight percent of an alkyl acrylate selected from the group consisting of ethyl acrylate, methyl acrylate, and mixtures thereof, 0 to 10 weight percent of a copolymerizable polyfunctional crosslinking monomer, and 0 to 10 weight percent of a copolymerizable graftlinking monomer having two or more addition polymerizable unsaturated reactive groups which participate in the polymerization reaction at substantially different rates said percentages of said alkyl acrylate, methyl methacrylate, polyfunctional crosslinking monomer and graftlinking monomer adding up to 100 percent; (B) an intermediate stage which is elastomeric and which is polymerized in the presence of the first stage, from a monomer mixture comprising 50 to 99.9 weight percent of an alkyl acrylate and/or alkyl methacrylate mixtures thereof wherein the alkyl groups contain 1 to 8 carbon atoms, 0 to 49.9 weight percent of a copolymerizable monoethylenically unsaturated monomer, 0 to 5.0 weight percent of a copolymerizable polyfunctional crosslinking monomer, and 0.05 to 5.0 weight percent of a copolymerizable graftlinking monomer as described above, said intermediate stage further characterized in that it would exhibit a glass transition temperature of 25° C. or less if the monomers were polymerized in the absence of the first stage; and (C) at least one final stage which is relatively hard and which is polymerized in the presence the first and intermediate stages from a monomer mixture of the monomers described above for the rigid thermoplastic polymer, the final stage further characterized in that it would exhibit a glass transition temperature of greater than 50° C. if the monomers were polymerized in the absence of first and intermediate stages, the graft linking monomer having two or more addition polymerizable unsaturated reactive groups which participate in the polymerization reaction at substantially different rates and the cross-linking monomer having a plurality of addition polymerizable unsaturated groups all of which participate in the polymerization reaction at about the same rate as one another.