Studies of polymers from cyclic dienes. V. Cationic polymerization of cyclopentadiene,influence of polymerization conditions on the polymer structure

Cationic polymerization of cyclopentadiene was studied with several Friedel-Crafts catalysts, and the influence of polymerization conditions on the polymer structure was investigated. Polycyclopentadiene contained higher amounts of the 1,2 structure when a stronger catalyst and a more polar solvent were used. This fact is discussed in terms of the tightness of the growing ion pair. The polymer structure did not vary with polymerization temperature in toluene solvent. In methylene chloride at around 0°C. the structural variation with catalysts was much smaller, suggesting a freer nature of the growing ion pair. The viscosity data also support the change in the structure of the ion pair under similar conditions. The use of aliphatic hydrocarbon solvents gave the highest contents of the 1,2 structure. This results was ascribed to the lack of solvation, considering the dependence of the polymer structure on the monomer concentration, which was found only in this solvent. Furthermore, isomerization during propagation was observed in polar solvents at higher temperature.