Syndiospecific polymerization of styrene catalyzed by CpTiCl2(OR) complexes

Five new CpTiCl2(OR) alkoxyl-substituted half-sandwich complexes, where R was methoxyethyl (1), methoxypropyl (2), methoxyisopropyl (3), o-methoxyphenyl (4), or tetrahydrofurfuryl (5), were synthesized, characterized, and tested as catalyst precursors for the syndiospecific polymerization of styrene. These precursors were more active than (η5-cyclopentadienyl)trichlorotitanium (CpTiCl3). The different structures of the alkoxyl ligands affected the activity slightly. When the polymerization was carried out in bulk, all the complexes (1–5) exhibited high activities, even at the low molar ratio of Al/Ti = 300. The syndiotactic polystyrene (s-PS) percentage of the polymer produced by alkoxyl-substituted complexes was much higher than that of CpTiCl3. The really active center might be described as [CpTiMe]+ · [MAOX]− · nMAO (where MAO is methylaluminoxane). The normal active species [CpTiMe]+ made up the core and the anion mass [MAOX]− · nMAO surrounded the core and constituted the outer shell circumstance. They activated the syndiospecific polymerization of styrene as a whole. For a high concentration of MAO, the function of the alkoxyl group was weak because of the limited proportion in the outer shell. For a low concentration of MAO, the proportion of alkoxyl ligands in the outer shell increased greatly, and their influence also became significant, as reflected in a higher s-PS percentage of the obtained 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. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1817–1824, 2001

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