Since Ishihara et al［1］ reported that a new macromolecule syndiotact ic polystyrene (s-PS) could be produced with high stereoregularity by using ( η5-Cp)TiCl3 activated with methylaluminoxane (MAO), more efforts were de voted to syntheses of new kinds of half-sandwich titanocenes and to elucidation of the relationship of precursor structure to its catalytic behavior［2～4］. The effect of the substituents attached to π-ligand on the styrene polym erization has been discussed［2～4］, but the effect of σ-bonded ligands has not been reported properly. 相似文献
Ethylene/styrene copolymerization catalyzed by half-titanocenes [Cp′TiX3 (Cp′ = cyclopentadienyl; X = halogen, alkyl etc.), linked half-titanocenes, and modified half-titanocenes expressed as Cp′TiX2(Y) (Y = anionic donor ligand)] have been reviewed. Results in the syndiospecific styrene polymerization using Cp′TiX2(Y)–MAO catalysts have also been summarized. The activity and molecular weight in the resultant (co)polymer (and styrene incorporation)
are highly affected by ligand (Cp′ and Y). It has been suggested that the cationic Ti(IV) plays a role in the copolymerization
whereas the neutral Ti(III) plays a role in the homopolymerization. 相似文献
Single‐site catalysts : Syndiospecific styrene polymerization promoted by single‐site ansa‐lanthanidocene catalysts proceeds selectively in a secondary (2,1) fashion, both at the initiation and propagation steps. The steric hindrance between the phenyl ring of the incoming styrene monomer and the ancillary ligands (Cp′, Flu′), induced by the change of either the bridge or the “active” R ligand in the catalyst precursor, is proposed to control the reactivity of the complexes (see scheme).
