Free-radical polymerizations using mixed initiator systems at two thermally distinct polymerization stages

Claim 1

A process for the free-radical polymerization of vinyl monomers, including vinyl aromatic monomers, comprises polymerizing said vinyl monomers in at least two thermally distinct polymerization stages, each between the temperatures of about 70° C. and 150° C. in the presence of at least two free-radical initiators, one of which initiators is particularly effective at the lowest temperature stage and has the formula ##STR3## and where R is an alkylene, alkynylene or alkenylene diradical, R 1 is alkyl, alkenyl, alkynl or alkoxy and R 2 is lower alkyl and R 3 is hydrogen or lower alkyl and a second of which initiators have a 10 hour half-life temperature of at least about 80° C., said temperature being at least about 15° C. above the 10 hour half-life temperature of the compound of Formula (I) wherein the same solvent is used for measuring the half-life of all initiators, wherein the initiator of Formula (I) allows completing the polymerization in a shorter time with the resulting polymer having a higher viscosity-average molecular weight than without the initiator of Formula (I).