80037-93-0

The reaction of tert-butyl peroxypivalate (2) with methyl methacrylate (3) has been studied by the radical trapping technique employing 1,1,3,3-tetramethyl-2,3-dihydro-1H-isoindol-2-yloxyl (1) as a scavenger. Thermolysis of 2 generated tert-butoxyl, tert-butyl, and methyl radicals in the ratios of 48:50:2 at 60 °C in 3. Both alkyl radicals underwent selective tail addition to 3. tert-Butyl radicals reacted about twice as fast as methyl radicals with 3. The absolute rate constant for addition of tert-butyl radicals to 3 was estimated to be 2.3 x 106 M-1 s-1 at 60 °C. The overall ratio of addition to H abstraction in the reaction of 2 with 3 was 5:1.

Examination of the title reaction in a range of solvents shows that the ratio of hydrogen abstraction to t-butoxy radical addition increases with increasing solvent polarity.In several cases there is a competition between solvent and methyl methacrylate for reaction with t-butoxy radicals.The implications of these findings for polymer structure are discussed.

The reactions of three electrophilic radicals, benzoyloxy, and t-butoxy, have been examined with a series of α,β-unsaturated esters; methyl acrylate, methyl methacrylate, and methyl crotonate.For the three monomers the ratio of hydrogen abstraction to double bond addition was found to increase and the ratio of head against tail addition to decrease in the series: benzoyloxy; phenyl; t-butoxy.Relative rates for these reactions have been determined and the factors influencing the mode of reaction are discussed.

Cumyloxy (1-methyl-1-phenylethoxy) radicals have been generated by thermolysis (60 deg C) of dicumyl hyponitrite in methyl methacrylate and styrene.The carbon-centred radicals formed by interaction of cumyloxyl with the respective monomers were trapped as stable adducts of 1,1,3,3-tetramethylisoindolin-2-yloxyl.Extensive hydrogen atom abstraction and methyl radical generation as well as double-bond addition were observed in methyl methacrylate.Styrene underwent only double-bond addition by both cumyloxy and methyl radicals.Some possible implications of these results for polymer structure are discussed.A kinetic study of the decomposition of dicumyl hyponitrite in cyclohexane at various temperatures gave k=7.7*1014exp(-13600/T) s-1 for the rate constant.Rate constants for the addition of cumyloxyl to methyl methacrylate (k ca.2*104 dm3mol-1s-1) and styrene (k ca. 2*105dm3mol-1s-1) at 60 deg C have been estimated