Influence of monomer concentration and dielectric constant on transfer reactions in the carbocationic polymerization of indene

The cationic polymerization of indene initiated with cumyl chloride and stannic chloride in solution in methylene chloride at -15 degrees C is controlled up to M-n = 20 000, with a low transfer to monomer constant (k(trM)/k(p) = 9 x 10(-4)). Experiments carried out in compensated media allowed kinetic measurements and showed that the sharp decrease of the M-n at high indene concentrations results from zero order transfer due to the change of dielectric constant (k(tr)/k(p) = 1.5 x 10(-3) for a dielectric constant of 5.4). In methylene chloride, for indene concentrations higher than 2 mol.L-1, the heat release of the fast reaction adds up to the zero order transfer to lower the molar masses. Bimodal distributions result from propagation on free ions and ion pairs.