CATIONIC POLYMERIZATION OF ALPHA-PINENE WITH THE BINARY CATALYST ALCL3/SBCL3

Oligomers of alpha-pinene (1) with relatively high molecular weight (number-average molecular weight M(n)BAR = 1 140, weight-average molecular weight M(w)BAR = 2 590) were obtained with the binary catalyst AlC13/SbCl3 toluene at -15-degrees-C ([AlCl3]0 = 42,5 mmol . L-1, mole ratio SbCl3/AlCl3 = 0,50). The yield was higher than 90%, and the dimer content was as low as 5 wt.-%. In contrast, AlCl3 alone gave predominantly dimers and lower oligomers in poor yield, whereas SbCl3 had no catalytic activity for 1. H-1 NMR analysis revealed that the structure of the higher-molecular-weight fraction (M(n)BAR = 2920, M(w)BAR = 3690) of the oligomers obtained with AlCl3/SbCl3 is 6, which consists of a cyclohexene ring with an endo-olefin group, most likely derived from the cationic monomer isomerization of alpha-pinene via the ring-opening of the cyclobutane unit. Effects of the reaction conditions on the polymerization rate and molecular weight were also investigated.