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

Abstract

AbstractSummary: The reactivity ratios r1 and r2 in copolymerizations of styrene and parasubstituted styrenes, for which r1 = 1/r2, are in contradiction with diffusion control for their propagation reactions. The cross propagation rate constants k12copol 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 k12capp of reactions of poly(p‐methylstyrene)± and poly(p‐methoxystyrene)± with π‐nucleophiles also increase with N, but with a much larger selectivity. This shows that k12copol and k12capp are not identical. The k, from 109 to 6 109 L mol−1 s−1, 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 104 – 105 L mol−1 s−1, 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.