Nippon Shokubai Co., Ltd.

Kimio Uda

Kazumi Fujioka

Fumioki Shimoyama

This invention provides a maleimide-based copolymer in which, because its molecular weight-retention ratio at high temperature is high, deterioration of physical properties by heating is little. Also, this invention provides a process wherein a maleimide-based copolymer is arranged so as not to heat more than necessity and thereby a maleimide-based copolymer containing only a small amount of residual volatile components is efficiently obtained without deterioration of physical properties. The maleimide-based copolymer is such as having a glass transition temperature of 170.degree. C. or higher, a weight-average molecular weight of 100,000 to 500,000, and a molecular weight-retention ratio of 90% or more when heated at 280.degree. C. for 10 minutes. When this copolymer is produced, volatile components are separated by supplying a polymer composition containing said copolymer and volatile components to a vent type screw extruder and operating this extruder under condition of a screw rotation number of 50 to 150 rpm.

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Hyogo, Japan

Kimio Uda