Predominant methyl radical initiation preceded by β-scission of alkoxy radicals in allyl polymerization with organic peroxide initiators at elevated temperatures

Abstract

Allyl monomers polymerize with difficulty and their polymerization yields polymers of medium molecular weight or oligomers. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry is a powerful tool for structural identification of oligomers; therefore, we aimed to use it to collect direct evidence for a full mechanistic discussion, including initiation and termination reactions. In the course of our investigation, which was concerned with the temperature dependence of the reinitiation reactivity of resonance-stabilized monomeric allyl radicals and was especially focused on polymerization behavior at elevated temperatures, we found by chance that any direct contribution of cumyloxy radicals to the initiation reaction was not observed in the polymerization of allyl benzoate with dicumyl peroxide (a typical peroxide initiator) at elevated temperatures. However, a methyl radical initiation preceded by β-scission of cumyloxy radicals predominantly occurred. This finding was extended to the generalization of an initiation reaction mechanism in allyl polymerization with organic peroxide initiators at elevated temperatures. Allyl benzoate (ABz) was polymerized using dicumyl peroxide (DCPO) at 130 °C; almost no direct contribution of cumyloxy radical to initiation reaction was observed. This was extended to other organic peroxide initiators; it was confirmed that the initiation by methyl radical generated by β-scission of alkoxy radicals occurred predominantly in allyl polymerization at elevated temperatures.