Cationic polymerization of α‐pinene with the binary catalyst AlCl₃/SbCl₃

Oligomers of α‐pinene ( 1 ) with relatively high molecular weight (number‐average molecular weight M n = 1140, weight‐average molecular weight M w = 2590) were obtained with the binary catalyst AlCl 3 /SbCl 3 in toluene at − 15°C ([AlCl 3 ] 0 = 42,5 mmol · L −1 , mole ratio SbCl 3 /AlCl 3 = 0,50). The yield was higher than 90%, and the dimer content was as low as 5 wt.‐%. In contrast, AlCl 3 alone gave predominantly dimers and lower oligomers in poor yield, whereas SbCl 3 had no catalytic activity for 1. 1 H NMR analysis reveled that the structure of the higher‐molecular‐weight fraction ( M n = 2920, M w = 3690) of the oligomers obtained with AlCl 3 /SbCl 3 is 6 , which consists of a cyclohexene ring with an endo‐olefin group, most likely derived from the cationic monomer isomerization of α‐pinene via the ring‐opening of the cyclobutane unit. Effects of the reaction conditions on the polymerization rate and molecular weight were also investigated.