Metallocenes, siloxy-substituted

Keywords Siloxy-substituted metallocenes Long-chain branching Rheological properties ... 

Fig. 2 Comonomer response of siloxy-substituted metallocene catalyst in copolymerisation of ethene with 1-hexene. The catalysts are (1) rac- Et(Ind)2ZrCl2 (2) rac- Et(2-ferf-BuSiMe2OInd)2 ZrCl2 (3) rac- Et(3-ferf-BuSiMe2OInd)2 ZrCl2 (4) meso- Et(2-tert-BuSiMe2OInd)2 ZrCl2 (5) meso- Et(3-terf-BuSiMe2OInd)2 ZrCl2...

Figure 2 presents examples of some siloxy-substituted metallocene catalysts (2-5) and, for comparison, an ordinary bis(indenyl) catalyst (1). The relative reactivity in ethene/1-hexene was investigated [44, 59, 60, 61, 62] in order to predict their copolymerisation ability compared with the conventional bis(indenyl) catalyst (1). 

The comonomer response (compare rac-catalysts 2 and 3 with the corresponding meso-catalysts 4 and 5 in Fig. 2) can be improved by using meso-isomers of C2 symmetric metallocenes [60]. In copolymerisation of ethene with 1-hexene the reactivity ratios of siloxy-substituted meso-isomers, catalysts 4 and 5, are comparable with those of Me2Si(2-Me-Benz(e)Ind)2ZrCl2 [52], which is considered to be a highly efficient copolymerisation catalyst. 

Figure 3a-b illustrate the LCB effect on the melt rheological properties. The response of the rheological behaviour to the copolymerisation ability and vinyl end group selectivity of the siloxy-substituted metallocenes has been investigated from their dynamic modulus curves. The frequency dependency of the dynamic modulus of the polyethenes produced with catalysts 2 is demonstrated in Fig. 3a. For comparison dynamic modulus for a linear polyethene, prepared by the catalyst -BuCp2ZrCl2, is shown in Fig. 3b. 

In conclusion, siloxy substitution has been demonstrated to provide a family of highly active metallocene catalysts that reveal optimum polymerization properties at low Al(MAO) concentrations. Good comonomer response and the reduction of the required MAO amount are highly desirable features from an industrial point of view. 

Title Metallocene Catalysts Containing a Cyclopentadienyl Ligand Substituted by a Siloxy or Germiloxy Group Containing an Olefinic Residue... 

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