CATALYTIC DIFFERENCE BETWEEN OXO ACIDS AND METAL-HALIDES IN THE CATIONIC OLIGOMERIZATION OF STYRENE

The structure and molecular weight (distribution) of products in the cationic oligomerization of styrene were found to be controlled by the proper choice of counteranions. Oxo acids as catalysts (AcC1O4, CF3.SO3H, and p-CH3C6H4SO3H.H2O) formed a linear unsaturated styrene dimer predominantly in benzene at 70 °C. On the other hand, metal halides yielded trimers (by BF3.OEt2 in C6H6) or tetramers (by BF3.OEt2 in (CH2Cl)2 and by SnCl4 or EtAlCl2 in C6H6) as the main product at 70 °C. Product distribution analysis showed that transfer constants (ktr/kp) for the oxo acids were larger than those for the metal halides and were independent of the chain length of the propagating species; in the case of the metal halides, transfer constants for short growing chains differed from those for long growing chains. The catalytic difference between the oxo acids and the metal halides was explained in terms of the interaction between a growing carbocation and a counteranion derived from a catalyst. The linear trimer or tetramer of styrene was produced in high yield by lowering initial monomer concentration and by using the metal halides as catalysts. © 1979, American Chemical Society. All rights reserved.