Patent ID: 6855786

Claim:
A method for preparing a methylmethacrylate-butadiene-styrene graft copolymer having superior anti-stress whitening properties, the method comprising steps of: a) preparing a rubber latex by conducting a polymerization using 65 to 95 parts by weight of butadiene and 5 to 35 parts by weight of vinyl-based monomers until the final polymerization conversion rate is 98% or more; b) adding 5 to 25 parts by weight of alkyl methacrylate to 75 to 95 parts by weight of the rubber latex prepared in step a) and conducting graft polymerization on the rubber latex to form a first-stage polymer; c) adding 0.0001 to 5 parts by weight of acrylate to 94 to 99.9999 parts by weight of the first-stage polymer prepared in step b) and conducting graft polymerization to form a second-stage polymer; and d) adding 5-30 parts by weight of ethylene unsaturated aromatic compound to 70-95 parts by weight of the second-stage polymer prepared in step c) and conducting graft polymerization to form a third-stage polymer.