Cationic Polymerization of Norbornene Derivatives in the Presence of Boranes

Cationic polymerization of 5-methylene-2-norbornene, 5-ethylidene-2-norbornene, 5-vinyl-2-norbornene, dicyclopentadiene, and norbornadiene-2,5 in the presence of boranes was systematically studied. It was found that B­(C₆F₅)₃ in combination with caprylic acid, 1-phenylethanol or water was a highly active catalyst for the polymerization of 5-alkylidene-2-norbornenes. The corresponding cationic polymers were obtained with up to yields 95% and with high molecular weights (M_w ≤ 430 000). The activity of 5-alkylidene-2-norbornenes in the polymerization using B­(C₆F₅)₃ containing systems was the highest among the other monomers (5-vinyl-2-nobornene, dicyclopentadiene, and norbornadiene-2,5). BF₃·O­(C₂H₅)₂ based catalysts turned out to be not so active for cationic polymerization of monomers compared with the systems containing B­(C₆F₅)₃. They produced polymers predominantly containing the addition (vinyl) units instead of isomerization units. The structure of the polymer main chain units depended on the nature of the monomers: in the case of norbornadiene-2,5, 5-methylene-2-norbornene, and 5-ethylidene-2-norbornene the transannular polymerization proceeded, while dicyclopentadiene and 5-vinyl-2-norbornene formed the addition type polymers under the studied conditions.