S. L. Saratovskikh

A New Catalytic System (2-PhInd)2ZrMe2/Al(iso-Bu)3 for the Synthesis of Stereoblock Polypropylene

A new efficient two-component homogeneous system consisting of (2-PhInd)2ZrMe2 and Al(iso-Bu)3 cocatalyst was developed for the synthesis of elastomeric stereoblock polypropylene. The catalytic behavior of this system was studied in toluene and liquid propylene. It was shown that a change in the Al/Zr molar ratio enables one to vary the system activity, the kinetic characteristics of the polymerization process, and the properties of polypropylene over wide ranges. For example, an increase in the Al/Zr ratio from 50 to 300 mol/mol is accompanied by an increase in the activity by a factor of 4, an increase in the molecular weight from 80 000 to 220 000, and a decrease in isotactic pentad content from 39 to 16%. It was found that the polymerization rate is proportional to the concentration of Al(iso-Bu)3 and to the square of the monomer concentration. Some assumptions about the nature of active centers and about reactions leading to the formation of these centers were made. A model for the formation of sequences of isotactic and atactic blocks was proposed. This model takes into account the multiple inversion of the active center (fast dynamic equilibrium) from the iso-specific to the nonspecific state during chain growth. This inversion is due to the coordination of an additional Al(iso-Bu)3 molecule. This model satisfactorily describes the pentad composition of polypropylene samples as a function of the Al/Zr ratio.

Syntheses of isobutylalumoxanes by triisobutylaluminum hydrolysis and their use as activators of dimethylated zirconocene in propylene polymerization

Isobutylalumoxanes of different composition were synthesized by the hydrolysis of triisobutylaluminum (TIBA) with crystalline hydrate CuSO4·5H2O and water taken as cooled ice or as vapor. The composition of the formed alumoxanes and the degree of water participation in their formation was monitored by 1H NMR. The hydrolysis of TIBA on CuSO4·5H2O is rather selective method of synthesis of alumoxanes. The synthesized alumoxanes were used for the activation of dimethylated zirconocenes rac-Me2Si(2-Me,4-PhInd)2ZrMe2 and rac-Et(2-MeInd)2ZrMe2 in propylene polymerization at the molar ratios Al/Zr = 50–750. It was concluded that the hydrolysis afforded several products with different structures and different activating ability. The systems with oligomeric forms of isobutylalumoxanes, especially those obtained by TIBA hydrolysis with water, showed the highest activity.

Influence of polymerization conditions on catalytic properties of the TiCl2{η2-1-[C(H)=N(2,3,5,6-tetrafluorophenyl)]-2-O-3,5-di-But-C6H2}2/MAO system in ethylene homopolymerization and copolymerization with α-olefins

Experimental data on ethylene homo- and copolymerization with higher a-olefins (hex-1-ene, oct-1-ene, and dec-1-ene) by the catalytic system TiCl2{η2-1-[C(H)=N(2,3,5,6-tetrafluorophenyl)]-2-O-3,5-di-But-C6H2}2/MAO in a Nefras medium and in toluene are presented. The catalytic system provides ultrahigh-molecular-weight polyethylene and incorporation of comonomer units at a level of 2–3 mol.% in both solvents. Nascent copolymers formed in Nefras (petroleum solvent), unlike those obtained in toluene, are characterized by two melting peaks in the DSC thermograms and only one when obtained in toluene. The molecular weight of polyolefins is efficiently controlled by the introduction of hydrogen into the system.

Metallocene systems in propylene polymerization: Effect of triisobutylaluminum and lewis bases on the behavior of catalysts and properties of polymers

For two stereospecific metallocene catalysts, namely, syndiospecific Ph2CCpFluHfMe2 and isospecific rac-Me2SiInd2ZrMe2, the introduction of Lewis bases into a reaction medium was shown to promote a marked rise in the efficiency of catalytic systems. In the case of the syndiospecific metallocene, the maximum effect of the base (a 10-fold increase in activity) was achieved using the (Ph2CCpFluHfMe2 + Ph3N)/CPh3B(C6F5)4 catalytic system in the presence of Al-i-Bu3 at a molar ratio of Al: Hf: B: N = 15: 1: 1: 1. When the polymerization of propylene was carried out in the presence of Al-i-Bu3 and Ph3N, an elastomeric stereoblock syndio/atactic polypropylene was produced. For the (rac-Me2SiInd2ZrMe2 + amine)/CPh3B(C6F5)4 catalytic system, a 15-to 30-fold increase in activity was observed upon introduction of amines of the aniline type: Me2NPh, Me-n-BuNPh, and NPh3.

Alkylation of toluene with dichloromethane in the presence of triisobutylaluminum and perfluorophenylborates

Abstract1H NMR method showed that in systems based on triisobutylaluminum (TIBA) and triphenylcyclopropenylium [Ph3C3]+[B(C6F5)4]–(CPB) or triphenylmethylium [Ph3C]+[B(C6F5)4]–(TB) perfluorophenylborates in a toluene–dichloromethane mixture the Friedel–Crafts process occurs with the formation of ditolylmethane (DTM) accompanied by the complete decomposition of TIBA to form isobutane. 19F NMR spectroscopy showed that the [B(C6F5)4]–anion decomposes in the systems to form B(C6F5)3 and HC6F5. The short-living [AlBu2i]+ cation formed in the reaction of perfluorophenylborates with TIBA is assumed to be the species initiating the process. It has been shown that CPB is less reactive than TB. The addition of a stoichiometric amount of Ph2CCpFluHfMe2 exerts no effect on the process with the CPB-containing system but inhibits the reaction in the case of TB.