SYNDIOSPECIFIC POLYMERIZATION OF STYRENE .1. TETRABENZYL TITANIUM METHYLALUMINOXANE CATALYST

Syndiospecific polymerization of styrene (S) was catalyzed by Bz4Ti/MAO (tetrabenzyl-titanium/methylaluminoxane). The product was separated into syndiotactic polystyrene (s-PS) and atactic polystyrene (a-PS) by extraction of the latter with boiling 2-butanone. Over the broad range of catalyst concentrations, compositions, and polymerization temperatures, the catalytic activity is 150 +/- 80 kg PS (mol Ti mol S h)-1 with 89 +/- 5% yield of s-PS (SY). The concentration of active species has been determined by radiolabeling. Only about 1.7% of Bz4Ti initiates syndiospecific polymerization at 60-degrees-C with values of rate constants for propagation and for chain transfer to MAO of 1.38 (M s)-1 and 5.2 x 10(-4) s-1, respectively. Nonspecific polymerization was initiated by 16.8% of the Ti having values of 0.056 (M s)-1 and 6.5 x 10(-4) s-1 for the rate constants of propagation and transfer, respectively. The effect of solvent polarity on the polymerization was studied using toluene mixed with chlorobenzene or o-dichlorobenzene as solvents. An increase of effective dielectric constant from 2.43 to 5.92 reduces the polymerization activity by a factor of two and lowers SY to mere 39%. In 1:1 toluene/chlorobenzene solvent mixture, it was found that 1.3% and 26% of the Bz4Ti initiate syndiospecific and nonspecific polymerizations of styrene, respectively. The Bz4Ti/MAO catalyst is poor in both productivity and stereo-selectivity.