Valence of active sites

In the polymerization of a-olefins, it is generally accepted that homogeneous catalysts based on group 4 metallocenes with MAO consist of cationic complexes. 

The catalyst for the styrene polymerization is prepared by the mixing of a compound with MAO. The catalytic activity of Cp Ti(OMe)3 is increased by the mixing time under room temperature, and the intensity of the electron spin resonance (ESR) spectrum (g=1.998) also showed an increase of the trivalent titanium species (Fig. 4.6). The polymerization activity of a titanium catalyst increases with an increase in the molar ratio of MAO to Ti. 

Ti(III) is considered to be the active species in the SPS polymerization. The H-NMR spectrum of the reacted materials between the titanium compounds and MAO does not show the titanium compound peaks. This also supports the trivalent titanium as the active site. Newman and Malanga [18] synthesized 

However, for Cp Ti(OMe)2, high conversions are obtained even without TIBA, and the conversion is higher than those for Cp Ti(OMe)3.This suggests 

Analogous studies were carried out by Dall occo et al. [21]. They found that in the absence of styrene, titanium had mainly a trivalent oxidation state. ESR measurements revealed the formation of an unidentified new Ti(III) species, possibly containing a Ti-H bond, suggesting a certain degree of P-hydrogen abstraction of the bonded polymer. 

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