Mechanistic Role of Lewis Bases and Other Additives in Quasiliving Carbocationic Polymerization of Isobutylene

Abstract

Isobutylene was initiated using 5-tert-butyl-1,3-di(2-chloro-2-propyl)benzene/TiCl4 in 60/40 hexane/methyl chloride: [IB]0 = 1.0 M, [TiCl4] = 0.12 or 0.24 M, [t-Bu-m-DCC] = 0.0119 M, T = −(40−80) °C. Most polymerizations contained a Lewis base or other additive, i.e., 2,4-dimethylpyridine, 2,6-di-tert-butylpyridine, tetra-n-butylammonium chloride, and/or pyridine hydrochloride. Polymerizations containing an additive yielded theoretical molecular weights, narrow polydispersity index, and apparent absence of irreversible chain termination (linear kinetic plots, ATR−FTIR spectroscopic data) and chain transfer, with two exceptions: coupled product was obtained at −40 °C, and protic initiation occurred with n-Bu4NCl alone. Polymerizations without an additive produced bimodal molecular weight distributions; however, essentially all chains were initiated from t-Bu-m-DCC. With an additive, Eact for propagation was −(5.3−5.5) kcal/mol. Removal of additives increased polymerization rate moderately at −80 °C but d...