Process for producing methyl methacrylate polymers

An improvement in the process of producing a methyl methacrylate polymer or a copolymer, said methyl methacrylate polymer or copolymer comprising at least 80% by weight of units derived from methyl methacrylate and at most 20% by weight of units derived from a copolymerizable ethylenically unsaturated compound, by a bulk polymerization procedure wherein the monomer or monomers are polymerized at temperatures of 150.degree. to 180.degree.C with a conversion of 50 to 80% in a polymerization zone and the polymerizaton mixture withdrawn from the polymerizaton zone is introduced into a separation zone where volatiles predominantly comprised of an unreacted monomer or monomers are separated from the polymer product, said separated volatiles being cyclically used as a part of the monomer feed for the polymerization, said improvement comprising substantially removing polymers having molecular weights of 186 to approximately 1,000 from the volatiles and cyclically using the volatiles so treated as a part of the monomer feed for the polymerization while maintaining the content in the volatiles of impurities having boiling points of lower than 200.degree.C at normal pressure within the range from 5 to 20% by weight based on the weight of the volatiles.