Carbonium Ion Polymerization of Norbornene and Its Derivatives

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Abstract
Cationic polymerizations of various bicyclo-(2,2,1)-heptane olefinic derivatives were examined, and the structures of the resulting polymers determined. Norbornene readily polymerizes to soluble polymer at-78°C, whereas 2-vinyl-5-norbornene yields predominantly soluble polymer at low temperatures (∼-78°C) and largely cross-linked product at higher temperatures (∼-30°C). The major polymerization mechanisms for norbornene and 2-vinyl-5-norbornene are similar. In each case, the reaction proceeds by opening of the endo double bond, and the repeat units are where R is H or vinyl. The reactivity difference between the endo and exo double bonds in 2-vinyl-5-norbornene is most likely due to the strained endo double bond. When the reactivity of the exo bond is enhanced by the introduction of a methyl group (2-isopropenyl-5-norbornene) both double bonds participate simultaneously in the polymerization, and cross-linked products are obtained.