Preparation of copolymers through cationic grafting. 6. Investigation of the mechanisms of transfer reactions in the polymerisation of α‐methylstyrene

Abstract

The mechanisms of transfer reactions in the polymerisation of α‐methylstyrene initiated with AlEt₂Cl from — 70°C to — 30°C have been investigated using cationic grafting on a poly(isobutylene‐co‐chloromethylstyrene). Besides the bimolecular transfer to the monomer, evidence has been found for the occurrence of a kinetically unimolecular transfer reaction, which may be attributed to transfer to the counter ion but might also result from transfer to the solvent. Transfer is not important at — 70°C and — 50°C. From the variation with conversion of the molar concentration of homopolymer chains (formed by transfer), transfer constants could be estimated (for transfer to monomer k_trM/k_p = 10‐⁵ at −70°C and 10‐⁴ at −50°C; for unimolecular transfer k_trk_p = 5 × 10‐⁵ mol litre⁻¹ at −70°C and 4 × 10‐⁴mol litre⁻¹ at −50°C). At both temperatures, initiation is not instantaneous but takes place throughout the polymerisation. At — 30°C, initiation seems to be rapid and quantitative, all the chloromethyl groups are modified and transfer becomes preponderant.