Patent ID: 7632892

Claim:
An acrylic copolymer composition comprising: an alkyl acrylate crosslinked polymer formed by the polymerization of 5-15 weight % of a crosslinking agent and alkyl acrylate monomer; and a non-crosslinked copolymer formed by the polymerization of 55-90 weight % of methyl methacrylate with 5-40 weight % of at least one monomer selected from the group consisting of alkyl acrylate compounds and alkyl methacrylate compounds, wherein the weights are based on the whole weight of the crosslinking agent and the monomer components, wherein the non-crosslinked copolymer has a weight average molecular weight of 4,100,00 to 9,100,000; and wherein the acrylic copolymer composition is prepared by a method of emulsion polymerization comprises: (a) (i) mixing 5-15 wt % of the crosslinking agent and the alkyl acrylate monomer to prepare an emulsion containing the alkyl acrylate crosslinked polymer having the degree of swelling of 3 to 10 in tetrahydrofuran and then adding 27.5-45 wt % of the methyl methacrylate, 2.5-20 wt % of the at least one monomer selected from the group consisting of the alkyl acrylate compound with an alkyl group of 1-18 carbon atoms and the alkyl methacrylate compound with an alkyl group of 2-18 carbon atoms, an emulsifier, a polymerization initiator, and a redox catalyst, to the emulsion containing the alkyl acrylate crosslinked polymer or (ii) mixing 27.5-45 wt % of the methyl methacrylate, 2.5-20 wt % of the at least one monomer selected from the group consisting of the alkyl acrylate compound with an alkyl group of 1-18 carbon atoms and the alkyl methacrylate compound with an alkyl group of 2-18 carbon atoms, an emulsifier, a polymerization initiator, and a redox catalyst to polymerize the monomers and then adding 5-15 wt % of the crosslinking agent and the alkyl acrylate monomer to the mixture; and (b) further adding 27.5-45 wt % of the methyl methacrylate, 2.5-20 wt % of the at least one monomer selected from the group consisting of the alkyl acrylate compound with an alkyl group of 1-18 carbon atoms and the alkyl methacrylate compound with an alkyl group of 2-18 carbon atoms, an emulsifier, a polymerization initiator, and a redox catalyst, to the resultant mixture of step (a).