Syndiospecific polymerization of styrene. I. Tetrabenzyl titanium/methylaluminoxane catalyst

Syndiospecific polymerization of styrene (S) was catalyzed by Bz4Ti/MAO (tetrabenzyltitanium/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 ± 80kg PS (mol Ti mo 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°C with values of rate constants for propagation and for chain transfer to MAO of 1.38 (M s)−1 and 5.2 × 10−4s−1, respectively. Nonspecific polymerization was initiated by 16.8% of the Ti having values of 0.056 (M s)−1 and 6.5 × 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 of 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 stereoselectivity.