High-temperature polymerization of styrene:: Mechanism determination with preparative gel permeation chromatography, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, and 13C nuclear magnetic resonance

An experimental study designed to elucidate mechanistic details regarding the thermal polymerization of styrene between 260 and 340degreesC is reported. The data show that back-biting to the third or fifth carbon from the chain end, followed by beta scission, is the dominant chain-producing reaction in the molecular weight development. This conclusion is supported by the C-13-NMR data coupled with preparative gel permeation chromatography, which show that the predominant low-molecular-weight oligomers are 2,4-diphenyl-1-butene and 2,4,6-triphenyl-1-hexene, that is, the products of the 1:3 and 1:5 back-biting/beta-scission reactions, respectively. The presence of head-to-head or head-to-tail branching, due to chain transfer to the polymer or back-biting, is shown to be negligible through C-13-NMR analysis. Finally, the distribution of terminal unsaturations, determined by the relative rates of termination, back-biting, and chain transfer to polymer, has been measured with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. This has shown that the back-biting/beta-scission reaction dominates the molecular weight development in comparison with either termination or chain transfer to the polymer. (C) 2004 Wiley Periodicals, Inc.