TIME-RESOLVED ELECTRON-SPIN-RESONANCE STUDY ON RADICAL POLYMERIZATION WITH (2,4,6-TRIMETHYLBENZOYL)DIPHENYLPHOSPHINE OXIDE - DIRECT ESTIMATION OF RATE CONSTANTS FOR ADDITION-REACTIONS OF DIPHENYLPHOSPHONYL RADICALS TO VINYL MONOMERS

Rate constants for addition reactions of diphenylphosphonyl radicals (Ph2P=O) to vinyl monomers were directly estimated by time-resolved electron spin resonance (ESR) spectroscopy. The rate constants were on the order of 10(6)-10(7) s-1 M-1, being 1 or 2 orders of magnitude larger than those of carbon-centered radicals, which were obtained by photolysis of benzoin, benzoin methyl ether, or 1-phenyl-2-hydroxy-2-methylpropanone-1. The fact that (2,4,6-trimethylbenzoyl)diphenylphosphine oxide (TMDPO) is a more effective initiator than alpha,alpha'-azobis(isobutyronitrile( (AIBN) was made clear in the radical polymerizations of vinyl pivalate at -30 and 70-degrees-C.