Stopped‐flow studies of cationic polymerizations

Abstract

AbstractThis paper summarizes results and conclusions from an extensive study by stopped‐flow methods of the rapid nonstationary phase of the polymerization by HClO4 in CH2Cl2 of styrene and some styrene derivatives. With styrene, this precursor reaction is detectable but unimportant at 0°C, becomes longer‐lasting as the reaction temperature falls, and at –97°C is the only contributor to the polymerization.Detailed studies at −60 and −80°C, identifying a transient absorption (λmax‐340 nm) as that of the (poly)styryl carbenium ion, lead to the conclusion that the reaction is a composite, with nonionic as well as ionic components. The rates of the polymerization by the two mechanisms can be distinguished only in favorable circumstances (presence of perchlorate salts) but can be interpreted to yield approximate rate constants for propagation by polystyryl carbenium ion‐perchlorate ion‐pairs, viz., kp± ∼ 2000 M−1S−1 at −80°C; 4000–5000 at −60°C. The rate constants of propagation by free ions are estimated as 10–20 times greater.