Synergistic impact modifier system for poly (alkylene terephthalates)

Claim 1

A synergistic impact modifier system for poly(C 2 to C 8 alkylene terephthalate) comprising A. one or more thermoplastic segmented copolyester elastomers, and B. one or more multiphase composite interpolymers comprising a final rigid thermoplastic phase polymerized in the presence of a first elastomeric phase polymerized from a monomer system selected from the group consisting of i. a monomer system comprising about 75 to 99.8% by weight C 1 to C 8 alkyl acrylate, 0.1 to 5% by weight crosslinking monomer, 0.1 to 5% by weight graftlinking monomer, said crosslinking monomer being a polyethylenically unsaturated monomer having a plurality of addition polymerizable reactive groups all of which polymerize at substantially the same rate of reaction, and said graftlinking monomer being polyethylenically unsaturated monomer having a plurality of addition polymerizable reactive groups, at least one of which polymerizes at a substantially different rate of polymerization from at least one other of said reactive groups; and ii. a monomer system comprising at least 50 percent by weight butadiene and 0 to 50 percent by weight of a different ethylenically unsaturated monomer, the weight ratio of B to A being about 1:2 to 4:1.