Mitsui Petrochemical Industries, Ltd.

Isaburou Higashi

Mikio Hashimoto

Tadao Yatsu

Yoshinori Akana

Masaki Kohsaka

In accordance with the present invention, there are provided polyester carbonate copolymers obtained by polymerization of a mixture of 20-80% by weight of an alkylene terephthalate oligomer [I] containing ethylene terephthalate as main structural units and having an intrinsic viscosity [.eta.], as measured at 25.degree. C. in o-chlorophenol, of less than 0.6 dl/g, and 20-80% by weight of a carbonate oligomer [II] containing 2,2-bis(4 -hydroxyphenyl)propane as main structural units and having an intrinsic viscosity [.eta.], as measured at 25.degree. C. in o-chlorophenol, of less than 0.6 dl/g, said copolymers having an intrinsic viscosity [.eta.], as measured at 25.degree. C. in o-chlorophenol, of 0.4-1.2 dl/g and a glass transition temperature (Tg) of 80.degree.-140.degree. C. with a single peak, and polyester resin compositions containing said copolymers, said resin composition being excellent in transparency, heat resistance and mechanical strength.

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Yamaguchi, Japan

Isaburou Higashi