HEAT-RESISTANT METHACRYLIC COPOLYMERS, PRODUCTION PROCESS THEREOF AND OPTICAL ELEMENTS

摘要

A process for production of methacrylic copolymers, characterized by charging a monomer mixture comprising 70 to 95 % by mass of methyl methacrylate, 0 to 15 % by mass of a-methylstyrene, 0 to 20 % by mass of styrene and 2 to 15 % by mass of maleic anhydride at a molar ratio of the sum of a-methylstyrene and styrene to maleic anhydride lying within the range of 1.0 to 2.5 into a polymerizer containing at least one polymeric membrane layer having an oxygen permeability of 1.5 x 10<-13> (mol•m<-2>•s<-1>•Pa<-1>) or below, sealing the resulting polymerizer, and polymerizing the monomer mixture under heating in a gas phase; methacrylic copolymers obtained by this process, which are reduced in yellowness and excellent in transparency and heat resistance; and optical elements made of the copolymers.