Structure−Reactivity Scales in Carbocationic Polymerizations: The Case of α-Methylstyrene

Abstract

The propagation rate constant, kp, for the cationic polymerization of α-methylstyrene (αMeSt) was determined. First, the polymerization of αMeSt was carried out initiated by the diαMeStHCl/SnBr4 initiator/coinitiator system in dichloromethane (DCM) or in DCM/methylcyclohexane (MeCHx) 1:1 (v/v) solvent mixture at −80 °C in the presence of allyltrimethylsilane (ATMS). Clean and quantitative addition of ATMS to the propagating end terminates the polymerization, and from the limiting conversion and molecular weights, the kp/kATMS ratio was calculated. The kp = (5.2 and 7.7) × 107 L mol−1s−1 in DCM and DCM/MeCHx 1:1 (v/v), respectively, were calculated from the kATMS values determined by the diffusion clock method. Competition polymerizations between αMeSt and each of the following monomers p-methylstyrene (pMeSt), isobutylene (IB), styrene (St), and p-chlorostyrene (pClSt) were performed in DCM/MeCHx 1:1 (v/v) at −80 °C. From the limiting conversions and molecular weights, the reactivity ratios kp/k12 were de...