THERMALLY INDUCED POLYMERIZATION OF AN ARYLVINYLBENZOCYCLOBUTENE MONOMER

The thermal polymerization of trans-p-(vinyltolyl)benzocyclobutene provides a soluble polymer of modest molecular weight. Spectroscopic analysis of this polymer suggests that the dominant mode of polymerization is the Diels-Alder reaction of the trans-alpha,beta-disubstituted olefin with an intermediate omicron-quinodimethane which arises from the thermally induced rearrangement of the benzocyclobutene functionality. The kinetics of this polymerization were studied by sampling an active polymerization and analyzing the reaction mixture via spectroscopic and chromatographic methods. A kinetic model for this polymerization is proposed in which the rate-limiting step is the first-order ring-opening rearrangement of the benzocyclobutene four-membered ring, followed by a relatively rapid Diels-Alder reaction. Observed rate constants calculated from the residual monomer content, alkene concentration, concentration of tetrahydronaphthalene repeat units, and oligomer molecular weights were in good agreement with the proposed polymerization mechanism and kinetics. The activation energy for the rate-limiting ring-opening rearrangement was calculated to be 35.4 kcal/mol.