Studies on the polymerization of bifunctional monomers. XVI. Cyclopolymerization of o‐divinylbenzene with triphenylmethyl fluoroborate and presumption of the presence of the free growing cation in this system

Cyclopolymerization of o ‐divinylbenzene was studied by using triphenylmethyl fluoroborate as initiator. The cyclization constant r c (ratio of the rate constant for intramolecular cyclization to that for intermolecular propagation) decreased with increase in polarity of the solvent. This solvent effect as well as the effect of catalysts reported previously could be accounted for by a revised model of the propagating species, where both the counter anion and the o ‐vinyl group were coordinated to the carbonium ion. The difference in activation energy between intramolecular cyclization and intermolecular propagation was 6.2 kcal/mole. This value was close to that obtained previously with BF 3 ·OEt 2 catalyst but greater than those for anionic and radical polymerizations. When tetraalkylammonium flouroborates were added to the polymerization system in methylene chloride, r c and the molecular weight of the polymer decreased. These results were ascribed to the decrease in the amount of the free propagating cation by the common ion effect.