O. N. Babkina

Catalytic systems Me2SiCp*NtBuMX2/(CPh3)(B(C6F5)4) (M?Ti, X?CH3, M?Zr, X?iBu) in copolymerization of ethylene with styrene

Catalytic activity of Me 2 SiCp * N t BuMX 2 /(CPh 3 )(B(C 6 F 5 ) 4 [M=Ti X=CH 3 (1); M=Zr, X= t Bu (2)1 systems in the ethylene/styrene (E/S) feed was examined. Experimental data revealed high activity for the catalytic system (1) for copolymerization ethylene with styrene, whereas the system with enhanced catalytic activity for ethylene homopolymerization (2) was temporarily blocked in the styrene presence yielding, even at high styrene content, homopolyethylene as the final product. Properties of thus obtained polymers were analyzed. Catalytic system (1) occurred very sensitive to S/E ratio in the comonomers feed. The 10-fold acceleration for ethylene consumption was shown in two experimental sets conducted at S/E = 1.3 ratio, 1 bar, and 7.5 bar ethylene pressure, respectively. The consequent enhancement in S/E ratio resulted in slowing down both ethylene consumption and catalyst deactivation rates. Atactic polystyrene was formed at high styrene content with the catalyst (1). Catalytic system (1) allowed design of products with the highest styrene content (20 mol %) at low ethylene pressure, moderate temperature, and high S/E ratio. The apparent activation energy estimated from the initial rates of ethylene consumption was 54.6 kJ/mol. Analysis of apparent reactivity factors (r E = 9 and r S = 0.04; r E x r S = 0.4) and 13 C-NMR copolymer spectra revealed an alternating tendency of the comonomers for active center incorporation. DSC measurements showed considerable decrease of melting points and crystallinity even for copolymers with low styrene content. The catalyst produced relatively high-molecular weight copolymers (140-150 kg/mol) even at 80°C.

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.

Effect of substituents on the catalytic properties of bis(cyclopentadienyl)zirconium dichloride complexes with polymethylaluminoxane and AlBu1 3/CPh3B(C6F5)4 cocatalysts in ethylene polymerization

The catalytic properties of the complexes (RCp)2ZrCl2 (R=H, Me, Pri, Bun, Bui, Me3Si,cyclo-C6H11), and Me2SiCp*NBuiZrCl2 (Cp*=C5(CH3)4) combined with the AlBui3−CPh3B(C6F5)4 cocatalyst in ethylene polymerization were studied. The specific activity of the substituted bis-cyclopentadienyl complexes decreases in the sequence: Me>Pri>Bun>Bui>Me3Si>cyclo-C6H11, which corresponds to the activity sequence for these complexes activated by polymethylaluminoxane (MAO) but is 4–20 times lower in absolute value. Comparison of the polyethylene samples obtained in the presence of the same complexes with MAO and AlBui3−CPh3B(C6F5)4 cocatalysts showed that polyethylene with much higher molecular mass, melting point, and crystallinity is formed in the presence of the ternary catalytic systems, and this indicates a different nature of the active sites of the catalytic systems. The effective activation energy of polymerization (≈3.6 kcal mol−1), first order with respect to monomer and ≈0.4 order with respect to organoaluminum component, was found for the (PriCo)2ZrCl2−AlBui3−CPh3B(C6F5)4 catalytic system. It was proposed on the basis of the kinetic data that AliBu3 enters into the composition of the active site to form a bridged heteronuclear cationic complex.

Catalytic activation of layered silicates for the synthesis of nanocomposite materials based on ultra-high molecular weight polyethylene

The effects of the structure of organomodified montmorillonite and the conditions of its catalytic activation by titanium and vanadium chlorides on the synthesis of nanocomposite materials based on ultra-high molecular weight polyethylene with an exfoliated structure by an in situ polymerization method were studied. It was shown that, with the use of organomodified montmorillonite with the interplanar spacing d001 = 1.6–1.8 nm, in which the alkyl radicals of a modifier are arranged in parallel to the basal silicate surfaces, the catalyst is adsorbed only on the external surface of particle, and it does not penetrate into the interlayer space (in this case, the exfoliation of a filler does not occur). With the use of montmorillonite samples with d001 > 2 nm with the packing of a modifier as paraffin-like mono- or bilayers, the catalyst is predominantly intercalated into the interlayer space of the layer silicate. As a result, in the course of polymerization, polyethylene is formed in the interlayer space of particles to facilitate the exfoliation of the filler in separate nanolayers. Conditions for the supporting of a catalyst onto organomodified montmorillonite, which prevent the transfer of the catalyst into solvent and the formation of a free polymer on the synthesis of nanocomposites under the conditions of suspension polymerization in n-heptane, were determined. The intercalation of a catalyst into the interlayer space of the particles of layered silicates and the exfoliation of filler particles in the course of the synthesis of composites were confirmed by X-ray diffraction analysis.

Spectral studies of bridged bisindenylmetallocenes and products of their reactions with polymethylalumoxane in toluene and dichloromethane in the visible region

Quantitative characteristics of changes in the energy of charge transfer from π-bonded ligands to metal are presented for the series of structurally similar ansa-metallocene complexes of IVB Group elements. The changes are caused by the solvation effect, replacement of σ-bonded chlorine ligands by methyl groups and of bridging ethylene groups by dimethylsilylene moieties, introduction of the methyl substituent into position 2 and phenyl substituent into position 4 of the indenyl system, variation of the transition metal in metallocene, and formation of complexes with polymethylalumoxane (MAO) at different AlMAO/Zr ratios. These effects are found to be additive.

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.