KINETICS OF ANIONIC POLYMERIZATION OF ALPHA-METHYLSTYRENE IN TETRAHYDROFURAN AND DIOXANE

The kinetics of anionic polymerization of α-methylstyrene have been studied in tetrahydrofuran (THF) at -30° to -60° with Na+ and K+ as cations and in dioxane at 5° to 20° with Na+, K+ and Rb+ as cations. In dioxane the rate constants for ion-pair propagation are in the order Na+ < K+ ≈ Rb+, as for styrene; but in THF the order is Na+ ≫ K+ and the activation energies are 0°7 and 5°5 kcal mole-1 (2°9 and 23 kJ mole-1) respectively. A comparison is made between the Arrhenius plots for eleven different propagation rate constants for the anionic polymerization of α-methylstyrene. The abnormal behaviour for the Li+/tetrahydropyran and Na+/THF systems is similar to that observed in the polymerization of styrene in THF and in dimethoxyethane with Na+ as cation. An analysis of the results for the α-methylstyrene/Na+/THF system has been made in terms of propagation by contact ion-pairs (c) and the more reactive solvent-separated ion-pairs (s), with the aid of spectrophotometric data which gives information concerning the relative proportions of the two types of ion-pair. It is concluded that E8 = 6 ± 1 kcal mole-1 (25 ± 4 kJ mole-1) compared with E(-) = 7 ± 2 kcal mole-1 (29 ± 8 kJ mole-1), while Ee is probably in the region 8-13 kcal mole-1 (33-54 kJ mole-1. The rate constants are in the order kc ≪ ks < k(-). © 1969.