Thermoplastic resin composition and method for preparing the same

A method for preparing a thermoplastic resin composition which comprises the step of melting and mixing, at 100.degree.-300.degree. C., an aromatic polyester resin (I) with

• 1 to 100% by weight of a graft polymerization precursor (A) which is obtained by first adding at least one vinyl monomer, at least one radical polymerizable or copolymerizable organic peroxide and a radical polymerization initiator to an aqueous suspension of an epoxy group-containing ethylene copolymer, then heating said suspension under such conditions that the decomposition of said radical polymerization initiator does not occur substantially, in order to impregnate said epoxy group-containing ethylene copolymer with said vinyl monomer, said radical polymerizable or copolymerizable organic peroxide and said radical polymerization initiator, and raising the temperature of said aqueous suspension, when the degree of said impregnation has reached at least 50% by weight of the original total weight of said vinyl monomer, peroxide and initiator, in order to copolymerize said vinyl monomer with said radical organic peroxide in said ethylene copolymer,
• 0 to 99% by weight of an epoxy group-containing ethylene copolymer (B), and
• 0 to 99% by weight of a vinyl polymer or copolymer (C) obtained by polymerizing at least one vinyl monomer,
• or alternatively melting and mixing said components (A), (B) and (C) previously at a temperature in the range of 100.degree. to 300.degree. C., and then melting and mixing the resulting mixture with said aromatic polyester resin (I).