Cationic polymerization of α‐pinene with aluminium‐based binary catalysts, 3. Effects of added base

Abstract

AbstractIn the presence of nucleophilic additives such as esters (ethyl benzoate, acetate, and chloroacetate), ethers (diethyl ether and 1,4‐dioxane), and ammonium salts (nBu4NCl), oligomers of α‐pinene with relatively high molecular weights (M̄n ≥ 1000) were obtained with the AlCl3/SbCl3 binary catalyst in toluene at 0°C ([AlCl3]0 = 42,5 mmol · L−1, Sb/Al = 0,50, [additive]0 = 10,6 mmol · L−1). The yield was 80–90 wt.‐%, and the dimer content was as low as 6 wt.‐%. Also in the polymerization at 25°C, the addition of ethyl benzoate increased the oligomer's average molecular weight (M̄n = 850) and decreased the dimer content (10 wt.‐%), in contrast to the low M̄n (350) and the high dimer content (40 wt.‐%) in the absence of the additive. The oligomers obtained in the presence of ethyl benzoate contained the repeating unit 1 which has an endo‐olefin group, at higher ratio than in the absence of the additive. Phenomenologically, the role of the additives is to retard the polymerization so as to proceed at a moderate rate even at high temperature above 0°C and thereby to suppress the dimer formation.