PURPOSE: To obtain the subject thermoreversible copolymer which is prepd. by grafting a polymer ingredient consisting of an N-substd. (meth)acrylamide deriv., etc., onto a vinyl polymer ingredient contg. vinyl chloride unit and exhibits excellent moldability and strength and is useful for medical materials, etc.

CONSTITUTION: By a method wherein, after polyvinyl chloride is dissolved in a solvent such as DMF and sodium diethyldithio-carbamate (DTC-Na), etc., are added thereto and the mixture is reacted under stirring at 60°C for 4 hr to prepare a DTC-polyvinyl chloride, an N-substd. (meth)acrylamide deriv. (e.g. N-isopropyl acrylamide, etc.), or a mixture of this compound with various copolymerizable monomers is added thereto and photopolymn. is performed by using a high pressure mercury vapor lamp, the objective graft copolymer wherein a polymer ingredient consisting of the N-substd. (meth)acrylamide deriv. or a copolymer ingredient consisting of this compound and various monomers is grafted onto a vinyl polymer ingredient contg. vinyl chloride unit, is obtd.