Effect of Cyclopentadienyl and Anionic Ancillary Ligand in Syndiospecific Styrene Polymerization Catalyzed by Nonbridged Half-Titanocenes Containing Aryloxo, Amide, and Anilide Ligands:  Cocatalyst Systems

Abstract

Styrene polymerizations with a series of nonbridged half-titanocenes of the type Cp′TiCl 2(L) [L ) O-2,6-i Pr2C6H3, Cp′ ) , C5Me5 (Cp*, 4′)] have been explored in the presence of MAO cocatalyst under various conditions. The catalytic activities for syndiospecific styrene polymerization with a series of half-titanocenes containing an aryloxo ligand, Cp′TiCl 2(O-2,6-i Pr2C6H3), were higher than those with the trichloro analogues, Cp′TiCl3, and the activity with a series of Cp* analogues (4, 4′, 5-8) and 1,3-Me2C5H3 analogues (2, 2′, 9, 10) were highly dependent upon the anionic donor ligand used. ( t BuC5H4)TiCl2(O-2,6-i Pr2C6H3) (11) exhibited a relatively high catalytic activity for syndiospecific styrene polymerization at 25°C when both [PhMe 2NH]B(C6F5)4 and a mixture of Al i Bu3/Al(n-C8H17)3 were used as the cocatalyst, and the activity with a series of (1,3-Me2C5H3)TiCl2(OAr) depended on the aryloxide ligand used. The role of the anionic donor ligand, like the aryloxide ligand, toward both the catalytic activity and the Mw values of polystyrene has thus been observed irrespective of the kind of cocatalyst employed.

Half-Titanocenes Containing Anionic Ancillary Donor Ligands: Effective Catalyst Precursors for Ethylene/Styrene Copolymerization

“…Taking into account these findings [58,87,88,91], it is thus highly assumed that the cationic Ti(IV) species, [Cp'TiR(Y)] + , likely play a role in copolymerization, and the active species containing an anionic ancillary donor ligand [assumed to be neutral Ti(III), Cp'TiR(Y)] proposed by Tomotsu et al [37,38] plays a role in syndiospecific styrene polymerization (Scheme 4) [90]. These results should also explain the reported finding that the catalytic activities and molecular weight of the resultant syndiotactic polystyrene in styrene polymerization using Cp'TiX 2 (Y)-cocatalyst systems were highly dependent upon the anionic donor ligand (Y), regardless of the kind of the cocatalyst used [90].…”

“…The resultant copolymers possessed lower M n values with unimodal, rather large PDI values (M w /M n = 1.50-1.62), which strongly suggests that a chain transfer reaction occurred to some degree. Note that the polymers prepared with the trichloride analogue (11) showed bimodal molecular weight distributions consisting of a mixture of PE and SPS, and the proportion of SPS increased at high temperature, due to an increase in the activity for syndiospecific styrene polymerization [58,87,88]. (Table 3); no distinct differences in the microstructures were seen between MAO and AFPB in the 13 C NMR spectra.…”

Dinuclear Metallocenes with a Modulated Biphenylene Bridge for Olefin Polymerization

“…A similar effect of the Cp ligand on the catalytic system has been observed with 5c and 5b and other reported mononuclear catalyst systems. [34][35][36] FULL PAPER The activities of the dinuclear complexes are slightly lower than those of the corresponding mononuclear systems. The extent of the activity decrease is more significant in 3b and 3c, which have a flexible diphenylethylene bridge, than in 3a, which has a rigid biphenylene bridge, thereby indicating the effect of the steric influence on the catalytic activity in styrene polymerization.…”

Olefin Polymerization with Half-Metallocene Catalysts

“…Although some M w values were different from those by the trichloride systems, the order in the M w values was similar to that by the trichloride systems [217]. It thus seems that the introduction of an electron-donating substituent on Cp' was effective in obtainment of high molecular weight SPS [217].…”