Elementary processes of the Ziegler catalysis, 7. Ethylene, α‐olefin and norbornene copolymerization with the stereorigid catalyst systems ipr[flucp]zrcl₂/mao and me₂si[ind]₂zrcl₂/mao

Abstract

Ethylene, a-olefin and norbornene copolymerization with the stereorigid catalyst systems iPr[FluCp]ZrC12/MAO and Me2Si[Ind]2ZrCl2/MAO b, SUMMARY:The stereorigid ansa-metallocene catalysts [2,4-cyclopentadien-1-ylidene(isopropylidene)fluoren-9-ylidene]zirconium dichloride/methylaluminoxane (iPr[FIuCp]ZrCl,/MAO) and [(dimethylsilylene)bis(~5-inden-1-ylidene)]zirconium dichloride/methylaluminoxane (Me,Si[Ind],-ZrCl,/MAO) are different in respect to the symmetry and, therefore, to the behaviour of the stereospecifity, in the size of the angle between the planes of the n-ligand systems and in the homopolymerization behaviour of ethylene and propene. The present paper concerns itself with comparing the investigations of the ethylene/a-olefin and the ethylenekycloolefin copolymerization with both catalyst systems. The main kinetic result for both catalysts is that the a-olefins show an accelerating effect on the ethylene polymerization rate during the copolymerization whereas norbornene shows exclusively a rate-decreasing effect. The acceleration effect can be explained by an increase in the concentration of active centres and/or an increase of the rate constant of the ethylene insertion. The analysis of the microstructures of the formed copolymers by the use of statistical models demonstrates that in copolymers with a high content of a-olefins, the experimental trial distributions can only be described satisfactorily with second-order Markovian statistics. That means that in this case the last two monomers have influence on the insertion of the subsequent monomer. A further main result of all investigated copolymerizations is that the r-parameters for the a-olefin insertion are more favourable for the system iPr[FluCp]ZrCl,/ MA0 than for the system Me,Si[Ind]2ZrCI,/MAO; the reason for this is the different size in the coordination gap aperture of the n-ligands. Furthermore, the r-parameters show only a small dependence on the chain length of the a-olefin. Finally, it is remarkable that the stereospecifity (syndiotactic or isotactic a-olefin blocks) remains intact in the copolymers. 0 1993, Hiithig & Wepf Verlag, Base1CCC 0025-1 16X/93/$05.00

Copolymerization of ethylene and 4-vinylcyclohexene by various metallocenes in the presence of Al(iBu)3/[Ph3C][B(C6F5)4]

“…The higher reactivity towards VCH of CAT-2 may be rationalized by the higher electron-donating effect of the fluorenyl group compared to the indenyl group and larger space so that bulky VCH can collide with the active central metal. Similar results were reported for the copolymerization of ethylene and higher α-olefins [13][14][15]. Copolymerization of ethylene and VCH was also carried out at various polymerization temperatures ranging from 30 to 70°C, in order to investigate the effect of temperature on the copolymerization behaviour.…”

“…1. However, 13 C NMR and Raman spectra of the resulting copolymers showed no peaks indicating the existence of VCH in polymer. As a result it might be assumed that the reactivity of VCH be negligible in the copolymerization of propylene and VCH using CAT-1 and CAT-2.…”

“…The lower initial rate results in a slower viscosity change of the polymerization medium so that the decay of R p after reaching its maximum is moderate. The VCH content incorporated in copolymer was determined by 13 C NMR spectroscopy according to the literature [2]. The results are summarized in Tab.…”

“…Fig. 4 shows the 13 C NMR spectrum of poly(ethylene-co-VCH) containing 8.04 mol-% of VCH (run no. 20 in Tab.…”

“…As a result they may be utilized for quantitative analysis. The quantitative analysis was carried out by comparing the intensity ratio of peaks of Raman spectra with the amount of VCH determined by 13 C NMR. The peaks at 1437 and 1295 cm -1 are used as reference peaks; they are assigned to be CH 2 deformation and twisting vibrations of polyethylene [16] …”