The butadiene polymerization in toluene at 25degreesC on VOCl3-(n-C4H9)Mg(iso-C8H17) catalytic system was investigated. The kinetic parameters of polymerization and molecular characteristics of polybutadiene were determined. It was shown that substitution of traditional organo-aluminum cocatalysts in trans-regulating vanadium systems does not have an effect on its stereospecificity, but significantly influences on the active centers reaction ability. (C) 2003 Wiley Periodicals, Inc.