Process for producing methacrylic polymer

A process for producing a methacrylic polymer wherein one perfect mixing type reactor, a plug flow type reactor which is a tubular reactor having a built-in static mixer and a volatile matter removing device are arranged in series, said process comprising:

• a) reducing the dissolved oxygen content in a mixture comprising one or more monomers to 2 ppm or less;
• b) in the perfect mixing type reactor, effecting continuous solution polymerization of the mixture in the presence of less than 5% by weight of an inert solvent or continuous bulk polymerization at a polymerization temperature of 110 to 160° C., in the presence of 0.01 to 1.0 mole % of a mercaptan compound as a chain-transfer agent and a radical initiator having a half-life period of 10 seconds to 1 hour at the polymerization temperature, by agitating the reaction mixture to make it substantially homogeneous, to form a reaction mixture having a polymer content in the perfect mixing type reactor in the range of 35 to 65% by weight;
• c) continuously withdrawing a portion of the reaction mixture from the perfect mixing type reactor and feeding the reaction mixture to the plug flow type reactor at a pressure that is not less than the vapor pressure of the reaction mixture throughout the plug flow type reactor;
• d) presetting the inner wall temperature of the plug flow type reactor to from 110 to 250° C., and passing the reaction mixture through the plug flow type reactor while polymerizing it by adding thereto and mixing therewith one or more radical initiators having a half-life period of not greater than 1,000 seconds at the inner wall temperature of the plug flow type reactor, so that the polymer content at the outlet of the plug flow type reactor is in the range of 50 to 85% by weight;
• and
• e) subsequently feeding the resultant reaction mixture to the volatile matter removing device to continuously separate and remove volatile matter, wherein the inner wall temperature of the plug flow type reactor is preset so that the plug flow type reactor is divided into two or more zones from the inlet toward the outlet and the inner wall temperature of one of said zones toward the outlet is higher than a zone toward the inlet, and
• wherein at one position immediately before the inlet of the plug flow type reactor, and at one or more positions within the plug flow type reactor, a radical initiator having a half-life period of not greater than 1,000 seconds at the inner wall temperature of the plug flow type reactor is added to and mixed with the reaction mixture.