| Polymerization of olefins such as styrene, one of many industrially important monomers, is a troublesome problem during storage, transportation and processing. The problem is attenuated by addition of polymerization inhibitors such as quinone derivatives. Despite the importance of quinone type inhibitors, their chemistry is poorly understood. The goal of this research is to better understand the reaction mechanism by measuring trapping rates and product studies of quinone type inhibitors with alpha-phenethyl radicals. cis Azo-alpha-phenylethane was used as a new simple, unimolecular, low temperature source of alpha-phenethyl radicals. The absolute rate constants of five quinone type inhibitors (QIO, BQ, QM, DTBQ and DPQI) with alpha-phenethyl radicals generated from cis azo-alpha-phenylethane were measured by the radical dock method using the stable nitroxide SG1 as the dock. We found that the trapping rate decreased in the order QIO>BQ>QM>DTBQ=DPQI. Also product studies of QIO, BQ, QM, and DPQI with alpha-phenethyl radicals were done to augment previous results. A detailed product study revealed the formation of semi-stable cyclohexadienones in some cases as well as a temperature-dependent product distribution from 1,4-benzoquinone. The trapping of alpha-phenethyl radicals is sometimes reversible, dimishing the efficiency of quinone inhibitors at elevated temperatures. |
