Can Propagation Reaction in Carbocationic Polymerization and Copolymerization of Styrene be Diffusion Controlled ?

Abstract

Summary:The reactivity ratios r 1 and r 2 in copolymerizations of styrene and parasubstituted styrenes, for which r 1 ¼ 1/r 2 , are in contradiction with diffusion control for their propagation reactions. The cross propagation rate constants k 12copol in copolymerization of styrene with p-chlorostyrene, p-methylstyrene and p-methoxystyrene have been shown to increase with their nucleophilicity parameter N. This is also not compatible with diffusion controlled cross propagation and propagation, but agrees with similar rate constants of propagation for these monomers. The capping rate constants k 12capp of reactions of poly( p-methylstyrene)AE and poly( pmethoxystyrene) AE with p-nucleophiles also increase with N, but with a much larger selectivity. This shows that k 12copol and k 12capp are not identical. The k ± p , from 10 9 to 6 10 9 L mol À1 s À1, obtained with p-chlorostyrene, styrene and p-methylstyrene by the Diffusion Clock (DC) method are not consistent with those derived from the ionic species concentration (ISC method) for indene, 2,4,6-trimethylstyrene and p-methoxystyrene of the order of 10 4 -10 5 L mol À1 s À1 , also measured for living polymerization. These last values are in agreement with those measured previously in nonliving systems, and with an approximate compensation between the reactivity of a monomer and that of the corresponding carbocation.

Revisiting living and apparently living carbocationic polymerizations

“…We have also shown [25,46] that diffusion controlled propagation and cross-propagation rate constants obtained by the DC method for p-chlorostyrene, styrene, p-methylstyrene and other monomers are not compatible with the reactivity ratios (r 1 , r 2 ) in their copolymerization. The ideal situation r 1 = 1/r 2 is in agreement with an inverse relationship between the reactivities of the monomer and the corresponding cation for a series of monomers as was proposed earlier [47].…”

“…We first showed in the case of isobutylvinyl ether that polymerizations said to be living occurred with transfer reactions and that a living process was only approached 46 POLIMERY 2014, 59, nr 1 (12) P ± + M P ± , M PM ± K M k p(1)…”