Cationic polymerization of 3-methylenecyclohexene and 2-methyl-1,3-pentadiene

To investigate the effect of a cyclic structure on the reactivity of conjugated dienes in cationic polymerization, a cyclic diene 3-methylenecyclohexene ( 1 ) and the corresponding linear diene 2-methyl-1,3-pentadiene ( 2 ) were synthesized and polymerized. Cationic polymerizations and copolymerizations showed that 1 was more reactive than 2 . The conjugated double bonds in 1 were proved to be less resonance-stabilized than that in 2 . However, the conjugate cation 1 was found to be more stable than that of 2 . The combination of these two factors made the cyclic diene more reactive than the linear d+. Cationic polymerizations of 2 were fast and non-stationary, giving low molecular weight polymers. The polymerizations proceeded mainly by the 1,4 route and to a smaller extent by the 1,2 route. A brief discussion on the stereochemistry in some electrophilic addition reactions of methyl-substituted butadienes is also given.