The reaction of benzylic radicals with quinoid inhibitors

Quinone inhibitors are used to prevent polymerization during the storage, transportation and processing of vinyl monomers. If left unchecked, polymerization will decrease the yield of vinyl monomers, result in higher production cost, and even ruin the processing equipment. Most of the published research on such compounds concerns polymer stabilization. The relatively few papers on quinone derivatives as polymerization inhibitors do not lead to a consistent picture of their chemistry. The four most important open questions are: (1) What is the inhibition mechanism? (2) What is the rate constant of these inhibitors with alkyl radicals? (3) Why do the products differ from one report to another? (4) Is the radical scavenging process reversible? All of these questions are important because they determine the effectiveness of inhibitors. We investigated the reaction of four inhibitors (BQ, QM, DPPI and 2,6-di-t-butyl-p-benzoquinone) with alpha-phenethyl radicals 4, which resemble the chain propagating radical in styrene polymerization. The ultimate goal of this research was to better understand the reaction mechanism and rates of alpha-phenethyl radicals with quinoid type radical scavengers