Syndiospecific polymerization of styrene catalyzed by CpTiCl2 (OR) complexes

Five new CpTiCl2(OR) alkorxl-substituted half-sandwich complexes, where R w as methoxyethyl(1), methoxypropyl (2), methoxyisopropyl (3), o-methoxypheny l (4), or tetrahydrofurfuryl (5), were synthesized, characterized, and test ed as catalyst pre cursors for the syndiospecific polymerization of styrene . These precursors were more active than (eta (5)-cyclopentadienyl)trichlor otitanium (CpTiCl3). The different structures of the alkoxyl ligands affect ed the activity slightly. When the polymerization was carried out in bulk, all the complexes (1-5) exhibited high activities, even at the low molar ra tio of Al/Ti = 300. The syndiotactic polystyrene (s-PS) percentage of the p olymer produced by alkoxyl-substituted complexes was much higher than that of CpTiCl3. The really active center might be described as [CpTiMe](+.)[MAO X](-.)nMao (where MAO is methylaluminoxane). The normal active species [CpT iMe](+) made up the core and the anion mass [MAOX](-).nMAO surrounded the c ore and constituted the outer shell circumstance. They activated the syndio specific polymerization of styrene as a whole. For a high concentration of MAO, the function of the alkoxyl group was weak because of the limited prop ortion in the outer shell. For a low concentration of MAO, the proportion o f alkoxyl ligands in the outer shell increased greatly, and their influence also became significant, as reflected in a higher s-PS percentage of the o btained polymer. The existence of the additional oxygen atom in the alkoxyl ligand stabilized the active species more effectively; this was reflected in the higher temperature of the maximum activities. (C) 2001 John Wiley & Sons, Inc.