T. M. Ushakova

Olefin polymerization on immobilized zirconocene catalysts containing alkylaluminoxanes synthesized on the support surface

Ethylene and propylene polymerization on immobilized catalysts of composition MMT-H2O/AlR3/Zr-cene (MMT = montmorillonite) and on the corresponding homogeneous catalysts of composition Zr-cene-MAO (Zr-cene = rac-Et(Ind)2ZrCl2, rac-Me2Si(Ind)2ZrCl2, rac-Me2Si(2-Me-4-Ph-Ind)2ZrCl2, rac-1-(9-η5-Flu)2-(5,6-Cp2-Me-1-η5-Ind)Et]ZrCl2) is considered. Here, the activating support for the zirconocenes is montmorillonite containing methylaluminoxane or isobutylaluminoxane synthesized directly on the monmorillonite surface by the partial hydrolysis of an alkylaluminum (AlMe3, Al(i-Bu)3, Al(i-Bu)2H) with the mobile water of the support (MMT-H2O/AlR3). The MMT-H2O/AlR3 supports are demonstrated to be effective activators for ansa-zirconocenes. The catalytic properties of the immobilized systems (process kinetics and efficiency, the molar mass of the resulting polymer, and the structure of the macromolecules) depend on the activating support and the zirconocene precatalyst. The complexes of the MMT-H2O/Al(i-Bu)3 support with all zirconocene precatalysts are more active in propylene polymerization than the same complexes of MMT-H2O/AlMe3. The zirconcenes immobilized on MMT-H2O/AlR3 afford polyethylene and polypropylene with a higher molar mass than the corresponding homogeneous systems. Furthermore, immobilization causes activesite heterogeneity. As compared to the homogeneous single-site catalysts of composition Zr-cene-MAO, the corresponding catalysts immobilized on MMT-H2O/AlR3/Zr-cene are more stereospecific in the case of rac-Me2Si(Ind)2ZrCl2 (C2 symmetry) and are less stereospecific in the case of rac-[1-(9-η5-Flu)2-(5,6-Cp-2-Me-1-η5-Ind)Et]ZrCl2 (Cs symmetry).

Heterogenized Methylaluminoxane and Isobutylaluminoxane as activators for metallocene catalysts

Heterogenized alkylaluminoxanes prepared in situ on the montmorillonite (MMT) surface by the partial hydrolysis of AIR3 with water of the support are effective activators for metallocenes. The thermal destruction of isobutylaluminoxane molecules in the MMT-H2O/Al(i-Bu)3 system has been studied by the temperature-programmed desorption method coupled with mass spectrometry (TPD-MS). The process begins at a lower temperature and is more complicated than the destruction of methylaluminoxane (MAO) in MMT-H2O/AlMe3. Isobutyl-substituted aluminoxane and the ansa-metallocene Me2Si(Ind)2ZrCl2 form metal-alkyl complexes that are more active in propylene polymerization than methyl-substituted aluminoxane. The TPD-MS study of the initial stages of gas-phase ethylene and propylene polymerization shows that the nature of the metallocene in the heterogenized metallocene catalysts is an essential factor in the distribution of active sites by the activation energy of the thermal destruction of active Zr-C bonds.

Raman structural study of reactor blends of ultrahigh molecular weight polyethylene and random ethylene/1-hexene copolymers

For the first time we carried out a detailed Raman study of reactor blends of high-density ultrahigh molecular weight polyethylene (UHMW PE) with random ethylene/1-hexene copolymers (CEHs). The blends were produced by consecutive two-step polymerization in the presence of rac-Me2Si(Ind)2ZrCl2/methylaluminoxane catalyst. The blends differed significantly in the CEH content as well as in the 1-hexene content in the CEH. We revealed a strong dependence of the Raman spectra of the blends on their structure. We found out that an increase in both the CEH content in the blend and the 1-hexene content in the CEH causes a reduction of the blend crystallinity and the total content of trans-conformers, while an increase in the content of gauche-conformers is observed. To investigate the effect of molecular weight on the neat polyethylene (PE) structure and Raman spectrum, we analyzed three neat PE samples with molecular weights of 34 000, 750 000, and 1 000 000. In order to better understand general regularities in the spectra, Raman spectra of solid n-alkanes C18H38 and C36H74 were also studied.

Application of zeolites as supports for catalysts of the ethylene and propylene polymerization

The Na-form of zeolite ZSM-5 (SiO2/Al2O3=24) was studied as a support for organometallic catalysts of olefin polymerization. Zeolite-fixed aluminoxanes were prepared by partial hydrosysis of trimethylaluminium with the zeolites internal water. It was shown that aluminoxanes synthesized on the zeolite surface form heterogenized complexes with Cp2ZrCl2 and Et[Ind]2ZrCl2 which are active for a long time in ethylene and propylene polymerization without addition of another aluminiumorganic cocatalyst. Yields were up to 1200 kg PE/molZr. bar.h. and 4000 kgPP/molZr.bar.h. The activation energy of ethylene and propylene polymerization in the presence of Na-ZSM-5(H2O)/AlMe3-Et[Ind]2 ZrCl2 is equal to 32 and 48,5 kJ/mol, respectively. Molecular weight and melting point of polyethylene obtained with such zeolite supported Zr-cene catalysts are higher than those of polyethylene formed with the corresponding homogeneous metallocene systems.

22-P-15-A new sorbent based on clinoptilolite-containing tuff modified by polyethylene

Publisher Summary This chapter discusses a novel sorbent based on clinoptilolite-containing tuff (CT) modified by polyethylene (PE). Clinoptilolite-containing tuff (CT) dust is modified by the catalytic polymerization of ethylene on the surface of CT particles. The compositions with 3-5wt.% of PE and 97–95 wt.% of CT are obtained. The thin PE coating formed on the CT particles is permeable to the filtrating water solutions. As a result of the encapsulation of the CT particles, the filter properties of this sorbent are improved. The ion-exchange characteristics of the modified CT (powder and pressed tablets) with respect to ammonium (NH 4 + ) and strontium (Sr 2+ ) cations are determined. CT dust–PE compositions retain the ion-exchange properties of initial CT.