Initiation mechanisms for radical polymerization of methyl methacrylate with tert-butyl peroxypivalate

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.