Processes for preparing copolymers

A process for preparing copolymers which comprises, in the order stated:

• (1) adding monomers containing unsaturated carbon-to-carbon bonds, two polymerization initiators, namely a first polymerization initiator with a 10 hour half-life temperature of from about 50.degree. C. to about 95.degree. C. and a second polymerization initiator with a 10 hour half-life temperature of from about 85.degree. C. to about 130.degree. C., and a solvent to a reaction vessel;
• (2) subsequent to step 1, purging the resulting solution with an inert gas;
• (3) subsequent to step 2, sealing the reaction vessel and pressurizing it by addition of an inert gas to a pressure of from about 20 to about 600 kiloposcals above ambient atmospheric pressure:
• (4) subsequent to step 3, maintaining the temperature within the pressurized reaction vessel at a substantially constant temperature within the range of from about 50 to about 100.degree. C. for a period of from about 60 to about 300 minutes;
• (5) subsequent to step 4, maintaining the temperature within the pressurized reaction vessel at a substantially constant temperature within the range of from about 80 to about 115.degree. C. for a period of from about 30 to about 300 minutes, wherein the temperature in step 5 is higher than the temperature in step 4:
• and (6) subsequent to step 5, maintaining the temperature within the pressurized reaction vessel at a substantially constant temperature within the range of from about 115 to about 160.degree. C. for a period of from about 30 to about 180 minutes, wherein the temperature in step 6 is higher than the temperature in step 5, wherein the resulting copolymer is substantially free of gel formation.