Evidence for the presence of cage reaction in the initiation step of thermal polymerization of styrenes by field desorption mass spectrometry

Field desorption mass spectrometry (FDMS) was applied to the study of the initiation mechanism of thermal polymerization of styrenes. The FD mass spectrum was measured for a cooligomer of α,α,β-trideuterostyrene and p-methoxystyrene produced by thermal polymerization using ethylbenzene as a solvent, and this was compared with the spectrum of an oligomer of p-methoxystyrene. The above two FD mass spectra showed characteristic differences, depending upon the number of hydrogen and deuterium atoms and upon the presence or absence of the methoxy group, in the oligomers. Molecular species observed in the spectra were identified based on these considerations. As a result, we could distinguish the “true trimer” produced from three monomers from the “cross trimer” produced from fragments of five monomers. It was found that the “true trimer” was the major constituent in the trimer region, and that the “true trimer” was produced mainly by the cage reaction between initiating radicals.