Ethylene copolymerization by half-titanocenes containing imidazolin-2-iminato ligands–MAO catalyst systems

Ethylene copolymerization with 1-hexene, styrene using half-titanocenes containing 1,3-dialkyl- and 1,3-diarylimidazolin-2-iminato ligands, Cp′TiCl2[1,3-R2(CHN)2CN] [Cp′ = Cp (1), tBuC5H4 (2); R = tBu (a), 2,6-iPr2C6H3 (b)], have been explored in the presence of MAO cocatalyst. Complex 1a exhibited remarkable catalytic activity for ethylene/1-hexene copolymerization, affording ultrahigh molecular weight copolymers with uniform molecular weight distributions (Mn = 1.07–1.31 × 106, Mw/Mn = 1.43–1.82). An opposite trend for effect of N-substituents in 1a,b toward the activity in ethylene and styrene homopolymerization was observed. The ethylene/styrene copolymerizations afforded poly(ethylene-co-styrene)s with uniform compositions and the polymerization by the tBu analogues (1a,2a) proceeded in a living manner with moderate activities, whereas the imidazolidin-2-iminato analogues, CpTiCl2[1,3-R2(CH2N)2CN] (R = tBu, Ph, 2,6-Me2C6H3), afforded a mixture of copolymer and homopolymers or exhibited negligible activity under the same conditions.

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► Notable activity for ethylene/1-hexene copolymerization by CpTiCl2[1,3-tBu2(CHN)2CN].
► Unique effect of N-substituents for the activity in ethylene, styrene polymerizations.
► Living ethylene/styrene copolymerizations attained by Cp′TiCl2[1,3-tBu2(CHN)2CN].
► Drastic ligand effect: imidazolin-2-iminato vs imidazolidin-2-iminato analogues.