Cationic polymerization of α‐pinene with aluminium‐based binary catalysts, 2. Survey of catalyst systems

Abstract

AbstractA series of metal halides (AlCl3, AlBr3, AlEtCl2, BF3 · OEt2, SnCl4, TiCl4, and WCl6) were employed in conjunction with antimony trichloride (SbCl3) for the cationic polymerization of α‐pinene in toluene at −15°C. The combinations of aluminium halides (AlCl3, AlBr3, and AlEtCl2) with SbCl3 gave high molecular weight oligomers (M̄n ≥ 700) in good yield (>80 wt.‐%) with low dimer contents (5–17 wt.%). The other metal halides, both in the absence and presence of SbCl3, gave large amounts (20–40 wt.‐%) of dimers along with low molecular weight oligomers. 1H NMR analysis of the obtained oligomers showed that they consist of two isomerized repeating units, one (1) unsaturated (with a cyclohexene ring) and the other (2) saturated (with a bornyl structure). The oligomers obtained with aluminium halides/SbCl3 contained higher amounts of unsaturated units 1 than those with aluminium halides alone. The higher the molecular weight, the larger the content of 1. Isomerization of α‐pinene slightly occurred in the course of the polymerization, and the structure of the isomers depended on the catalyst systems. These results show that the aluminium halide/SbCl3 binary systems promote the ring‐opening of the cyclobutane unit in α‐pinene to give higher molecular weight oligomers.