INITIATION MECHANISMS IN COPOLYMERIZATION - REACTION OF T-BUTOXYL RADICALS WITH CO-MONOMERS ETHYL VINYL ETHER AND METHYL-METHACRYLATE

The radical trapping technique employing 1,3,3-tetramethyl-1,3-dihydro -1H-isoindol-2-yloxyl as a scavenger has been used to investigate the reaction of t-butoxyl radicals with mixtures of ethyl vinyl ether and methyl methacrylate. The range of identified products includes those f rom both addition and hydrogen abstraction with both monomers, head ad dition with ethyl vinyl ether, and some second monomer addition produc ts. Relative rate constants have been obtained for Various pairs of co nstituent reactions. t-Butoxyl radicals add to ethyl Vinyl ether one t o two times faster than to methyl methacrylate, depending on which mon omer is in excess. The ratio is less than 1 in nonolefinic solvents an d as high as 6 in t-butanol. This solvent effect is thought to be due to the radicals complexing to either methyl methacrylate or t-butanol (H-bonding), thereby increasing its electrophilic character. (C) 1997 John Wiley & Sons, Inc.