Cyclization and Reduced Pendant Vinyl Group Reactivity during the Free-Radical Crosslinking Polymerization of 1,4-Divinylbenzene

Abstract

Free-radical cross-linking polymerization of 1,4-divinylbenzene (1,4-DVB) has been investigated in toluene. The monomer concentration was less than 5 w/v%. Conversion of monomer and pendant vinyl groups, weight-average molecular weight M w , and intrinsic viscosity [η] of the polymers were measured as a function of the reaction time up to the onset of macrogelation. A kinetic model was used to calculate the extent of cyclization and reduced pendant reactivity from the experimental data. Fraction of pendant vinyls in cycles, number of multiple cross-linkages, and the reactivity ratio of pendant to monomeric vinyl were evaluated as a function of the polymerization temperature, initial concentrations of 1,4-DVB and the initiator as well as the amount of styrene as a comonomer. The results indicate that 30-60% of pendant vinyls are used by cyclization reactions and, on average, 100-800 multiple cross-linkages occur per one intermolecular cross-link formed. The average pendant reactivity for intermolecular links is 2-3 orders of magnitude lower than the monomeric vinyl reactivity. These results were found to be in accord with the observed weak M w dependence of [η] of the polymers and their stability against degradation by ultrasonic waves. The critical exponent γ suggests non-mean-field behavior in the vicinity of the gel point