Cationic polymerization of cyclic dienes. V. Polymerization of the methylcyclopentadiene

Methylcyclopentadiene (MCPD) has been polymerized with cationic catalysts in toluene solution at −78°C. to a white powdery polymer, whose intrinsic viscosity in benzene solution at 30°C. ranged from 0.1 to 0.5. The comparison of the rate of homopolymerization of MCPD with that of cyclopentadiene (CPD) and the copolymerization of MCPD and CPD indicated that MCPD is much more reactive than CPD. It was suggested that the high stability of cycloalkenyl cation is responsible for the high reactivity of cyclic dienes. Infrared and NMR spectroscopy on polymethylcyclopentadiene showed that almost all of the monomer units in polymethylcyclopentadiene produced under the present conditions have a trisubstituted double bond. The mechanism of the initiation reaction in the polymerization of cyclic dienes is also discussed.