Process for production of thermoplastic copolymer

A process for producing a thermoplastic copolymer, in which a copolymer (A) containing (i) unsaturated carboxylic acid alkyl ester units and (ii) unsaturated carboxylic acid units is produced and in succession heat-treated to undergo an intramolecular cyclization reaction through a dehydration and/or dealcoholization reaction, wherein a thermoplastic copolymer (B) containing (iii) glutaric anhydride units, each represented by the following general formula (1), and the (i) unsaturated carboxylic acid alkyl ester units is produced, said process comprising:

• supplying into a polymerization vessel, in the absence of water, a monomer mixture containing an unsaturated carboxylic acid alkyl ester monomer and an unsaturated carboxylic acid monomer as raw material's, a raw material mixture solution containing 0.1 to 2.0 parts by weight of a chain transfer agent per 100 parts by weight of the monomer mixture, and a radical polymerization initiator with a half life of 0.01 to 60 minutes at the polymerization temperature in a polymerization step, and
• performing continuous polymerization while the content of the copolymer (A) in the polymerization vessel is kept at 20 to 80 wt %, to continuously produce a copolymer solution (a) consisting of the copolymer (A) and an unreactive monomer mixture, whereby in succession, the copolymer solution (a) obtained in the polymerization step is continuously supplied into a devolatilization apparatus and subjected to devolatilization in a range from the polymerization temperature to lower than 300° C. at a reduced pressure of 200 Torr or less to separate and remove the unreactive monomers in a devolatilization step, and the copolymer (A) obtained in said devolatilization step is continuously supplied into a cyclization apparatus to be heat-treated in the cyclization apparatus at a temperature of 200° C. to 350° C. so as to conduct an intramolecular cyclization reaction in a cyclization step to produce thermoplastic copolymer (B),
• wherein R1 and R2 denote, respectively independently, any one selected from a hydrogen atom and alkyl groups with 1 to 5 carbon atoms.