Copolymer, thermoplastic resin composition, and process for producing the same

The present invention relates to a maleimide-based and/or an unsaturated dicarboxylic acid anhydride-based copolymer excellent in heat resistance, transparency, mechanical strength and moldability, unlikely to thermal degradation, small in an extent of coloration and deterioration occurring in the process of molding, and superior in appearance after molding, a thermoplastic resin composition comprising said copolymer and a rubbery polymer, and processes for producing said copolymer and said thermoplastic resin composition. A copolymer comprising a maleimide-based monomer unit and/or an unsaturated dicarboxylic acid anhydride-based monomer unit, where the copolymer contains an unreacted maleimide-based monomer and/or an unsaturated dicarboxylic acid anhydride-based monomer in an amount of 200 ppm or less and an adduct of a compound other than the polymerized units of the copolymer and the maleimide-based monomer and/or unsaturated dicarboxylic acid anhydride-based monomer in an amount of 0.1 to 3,000 ppm.