DETERMINATION OF RATE CONSTANTS OF FREE-ION AND PAIRED-ION PROPAGATIONS IN THE CATIONIC POLYMERIZATION OF STYRENE BY TRIFLUOROMETHANESULFONIC ACID

The propagation step of the cationic polymerization of styrene was studied in detail with the CF3SO3H initiator in dichloroethane at -1 to 30 °C. The apparent rate constant of propagation Kp, app was estimated from the time course of the carbocation (P+) formation and monomer consumption by the combination of stopped-flow spectroscopy and the rapid quenching technique. Then kp, app was separated into the rate constants of the free-ion and paired-ion propagations (kp+ and kp±) on the basis of the dependence of kpfipp on [P+] and of the effect of a common ion salt. The values of kp+ and kp± were (2-30) × 105 M-1 s-1 and (0.4-1.2) X 105 M-1 s-1, respectively, in the temperature range studied. The ratio kp+ / kpα was 6-24, which is much smaller than those observed for the anionic polymerization. © 1979, American Chemical Society. All rights reserved.