Highly Stable Catalysts for the Stereospecific Polymerization of Styrene

The synthesis of eight new catalyst precursors is described, and their catalysis of syndiospecific styrene polymerization when activated by methylaluminoxane (MAO) is compared with IndTiCl 3 . Phenyl substitution increases polymerization activity ( A ) in the order 1,3-Ph 2 Ind < 2-PhInd < 1-PhInd; the opposite trend was observed for the yield (SY) of syndiotactic polystyrene ( s -PS). The optimum polymerization temperature ( T p ) is 50 °C; an increase of T p decreases A, SY, and molecular weight (MW) of s -PS. Benz[ e ]IndTiCl 3 ( 6a ) as well as the 2-methyl ( 6b ) and 1,2,3-trimethyl ( 11 ) derivatives have been synthesized. Complexes 6a/ MAO and 6b/ MAO have exceedingly high values of A ≈ 1.8 × 10 8 g of PS/(mol of Ti·mol of styrene·h) for a turnover rate of 450 s - 1, SY over 92%, and MW ≈ 5 × 10 5 . These parameters were only slightly lowered at T p = 100 °C, indicating very thermally stable, catalytically active species. These catalyst precursors are stable in solution toward air and moisture up to 48 h and are indefinitely stable in the solid state. Though 11 /MAO has a lower A, it has a higher SY which changes to lesser degrees with increase in T p than for either 6a or 6b /MAO. Attempts to make benz[ f ]indenyltrichlorotitanium have so far been unsuccessful.