1H-, 13C-NMR and ethylene polymerization studies of zirconocene/MAO catalysts: effect of the ligand structure on the formation of active intermediates and polymerization kinetics

Abstract

Using 1 Hand 13 C-NMR spectroscopies, cationic intermediates formed by activation of L 2 ZrCl 2 with methylaluminoxane (MAO) in toluene were monitored at Al/Zr ratios from 50 to 1000 (L 2 are various cyclopentadienyl (Cp), indenyl (Ind) and fluorenyl (Flu) ligands). The following catalysts were studied: (Cp-R) 2 ZrCl 2 (R0/Me, 1,2-Me 2 , 1,2,3-Me 3 , 1,2,4-Me 3 , Me 4 , Me 5 , n-Bu, t-Bu), racethanediyl(Ind) 2 ZrCl 2 , rac-Me 2 Si(Ind) 2 ZrCl 2 , rac-Me 2 Si(1-Ind-2-Me) 2 ZrCl 2 , rac-ethanediyl(1-Ind-4,5,6,7-H 4) 2 ZrCl 2 , (Ind-2-Me) 2 ZrCl 2 , Me 2 C(Cp)(Flu)ZrCl 2 , Me 2 C(Cp-3-Me)(Flu)ZrCl 2 and Me 2 Si(Flu) 2 ZrCl 2. Correlations between spectroscopic and ethene polymerization data for catalysts (Cp-R) 2 ZrCl 2 /MAO (R 0/H, Me, 1,2-Me 2 , 1,2,3-Me 3 , 1,2,4-Me 3 , Me 4 , Me 5 , n-Bu, t-Bu) and rac-Me 2 Si(Ind) 2 ZrCl 2 were established. The catalysts (Cp-R) 2 ZrCl 2 /AlMe 3 /CPh 3 ' B(C 6 F 5) 4 ((R0/Me, 1,2-Me 2 , 1,2,3-Me 3 , 1,2,4-Me 3 , Me 4 , n-Bu, t-Bu) were also studied for comparison of spectroscopic and polymerization data with MAO-based systems. Complexes of type (Cp-R) 2 ZrMe ' 1/Me (-Al /MAO (IV) with different [Me-MAO] (counteranions have been identified in the (Cp-R) 2 ZrCl 2 /MAO (R 0/n-Bu, t-Bu) systems at low Al/Zr ratios (50 Á/200). At Al/Zr ratios of 500 Á/1000, the complex [L 2 Zr(m-Me) 2 AlMe 2 ] ' [Me-MAO] ((III) dominates in all MAO-based reaction systems studied. Ethene polymerization activity strongly depends on the Al/Zr ratio (Al/Zr 0/200 Á/1000) for the systems (Cp-R) 2 ZrCl 2 /MAO (R 0/H, Me, n-Bu, t-Bu), while it is virtually constant in the same range of Al/Zr ratios for the catalytic systems (Cp-R) 2 ZrCl 2 /MAO (R0/1,2-Me 2 , 1,2,3-Me 3 , 1,2,4-Me 3 , Me 4) and rac-Me 2 Si(Ind) 2 ZrCl 2 /MAO. The data obtained are interpreted on assumption that complex III is the main precursor of the active centers of polymerization in MAO-based systems.

Studies of the Nature of the Catalytic Species in the α‐Olefin Polymerisation Processes Generated by the Reaction of Diamido(cyclopentadienyl)titanium Complexes with Aluminium Reagents as Cocatalysts

“…The broadness could be due to the closer position of the methyl group, initially bound to titanium, to the ''diversification'' centres provided by different Lewis acidic sites present in MAO. [62,63] The broadening of Ti-Me resonances of an adduct with MAO has also been reported by Talsi et al [59,64] When the polarity of the solvent is high, as in this case, methyl group abstraction by MAO is favoured and solventseparated ion pairs are preferentially formed.…”

Activation of rac‐Me2Si(ind)2ZrCl2 by Methylalumoxane Modified by Aluminum Alkyls: An EPR Spin‐Probe, 1H NMR, and Polymerization Study

“…[4][5][6][7][8][9][10][11][12] To be effective, MAO must be used in large excess over the transition metal component. For practical applications, it would thus be desirable to decrease the amount of MAO activator.…”

Multi-Alkenylsilsesquioxanes as Comonomers and Active Species Modifiers of Metallocene Catalyst in Copolymerization with Ethylene

“…The NMR spectroscopy was successfully applied to investigate the intermolecular structure of the ionic species relevant to the catalytic homogeneous polymerization [33][34][35][36][37][38][39][40][41][42]. These literature data provided important information on the structures of intermediates formed upon the activation of metallocene with MAO in toluene.…”

“…This phenomenon is associated with the influence of the POSS comonomer on transformation of the bimetallic metallocene species 1 (inactive form) into 2 or 3 complexes (precursors of the active form). However, the observed metallocene species 2 and 3 were dominant in the catalytic system in this case, even at the low Al/Zr ratio of 50 mol/mol, which is unusual for this group of catalysts [33][34][35][36][37][38][39][40][41][42]. It is probable that the modification of the catalytic system by the POSS compound resulted in much higher activity of the catalytic system in ethylene copolymerization with the POSS-6-3 comonomer as compared to homopolymerization of ethylene ( Figure 2).…”