N. M. Bravaya

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.

Immobilized osmium clusters in the processes of liquid-phase oxidation of cycloxehene

The reaction of catalytic hydroxylation of olefins by organic hydroperoxides in the presence of osmium carbonyl clusters supported on polymer matrices is studied. The process occurs with the predominant formation of unsaturated alcohols. The oxidative coupling of olefins with the formation of nonconjugated dienes and in which the double bonds remain intact occurs in parallel. In the course of the reaction, changes in the chemical structures of the initial osmium clusters are not observed.

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.

Mechanochemical synthesis of triphenylmethylium and triphenylcyclopropenylium tetrakis(pentafluorophenyl)borates

A possibility of application of mechanochemical method for the synthesis of triphenylmethylium and triphenylcyclopropenylium tetrakis(pentafluorophenyl)borates by the solvent-free reaction of solid starting compounds was studied. Some specific features of these reactions were discovered. Preparative methods for the mechanochemical synthesis of these salts were developed. This method makes the process shorter and excludes the use of solvents in the synthesis.

Highly active three-component catalytic systems based on dialkylzirconocenes, triisobutylaluminum, and perfluorophenyl borates for synthesis of low-molecular-weight polyethylene

The catalytic properties of the zirconium complex with “constrained geometry” Me2SiCp*NBu1ZrX2 (Cp*=C5Me4, X=Cl (1a), Me (1b)) and bridged bis(cyclopentadienyl)zirconocene Me2SiCp2ZrX2 (X=Cl (2a), Me (2b)) during their activation with triisobutylaluminum/perfluorophenyl borates (TIBA/LB(C6F5)4, L=CPh3 (3), Me2HNPh (4)) in ethylene polymerization under a monomer pressure of 2–20 atm were studied by comparison. Both dichloride complexes exhibit moderate activity under the action of the combined TIBA/3 activating agent and give linear high-molecular-weight polyethylene (PE). The interaction of the dimethyl complexes with TIBA/3(4) afford active sites in which the growing polymeric chain is intensely transferred to the monomer, due to which low-molecular-weight PE is formed. The dichloride complexes affected by TIBA/4 also afford low-molecular-weight PE. Analysis of the structure of the polymeric products (1H NMR spectrometry, IR spectroscopy), molecular-weight parameters of the PE samples (gel permeation chromatography (GPC)), and kinetics of polymerization suggested that the active site contains AlBui3 as a heteronuclear bridged cationic complex. The influence of various basic substrates (the products of chain transfer with the terminal vinyl groups, the dimethylaniline fragment of borate4 or other amine specially introduced into the reaction mixture) on the catalytic properties of the Zr−Al site was revealed. The polymerization rate and molecular-weight parameters of PE as functions of the reaction temperature, ethylene pressure, and modifying additives were studied.

EFFECT OF SUBSTITUENTS ON THE CATALYTIC PROPERTIES OF BIS(CYCLOPENTADIENYL) ZIRCONOCENE DICHLORIDES IN POLYMERIZATION OF ETHENE

Comparative analysis of catalytic activity of substituted bis(cyclopentadienyl)zirconium dichlorides with the general formula (RnCp)2ZrCl2 (Cp2ZrCl2, (MeCp)2ZrCl2, (PriCp)2ZrCl2, (Pri2Cp)2ZrCl2, (BunCp)2ZrCl2, (BuiCp)2ZrCl2, (ButCp)2ZrCl2, Cp*2ZrCl2 (Cp*=Me5C5), (Me3SiCp)2ZrCl2, (cyclo-C6H11Cp)2ZrCl2, and [(cyclo-C6H11)2Cp]2ZrCl2) in ethene polymerization using polymethylalumoxane as the cocatalyst was performed. The molecular mass characteristics of the polyethylene samples obtained were determined. A linear correlation of the specific activity of the catalysts and the turnover number with the electronic and steric characteristics of substituents at the Cp ring of the complexes was established for the first time. Analysis of the polymerization kinetics and the obtained correlation between the specific activity of the complexes and molecular mass characteristics of the polyethylene samples suggest that alkyl substituents participate in reactions responsible for the restriction of the polymer chain growth and regeneration of the active center. These interactions most likely involve associates of AlMe3 with polymethylalumoxane molecules.

PREPARATION AND REACTIVITY OF METAL CONTAINING MONOMERS. XLIII: SYNTHESIS AND PROPERTIES OF COPOLYMERS OF STYRENE OR ACRYLONITRILE WITH TRIOSMIUM CARB ONYL CLUSTER MONOMERS

The peculiarities of radical copolymerization of styrene or acrylonitrile with triosmium carbonyl clusters whose ligand environments incorporate groups with multiple bonds capable of polymerization (4-vinylpyridine, allylamine, acrylic acid) are described. Using IR and NMR spectroscopy under the model conditions, it was shown that no side processes occur during the reaction of comonomers and azo-bis-isobutyronitrile, an initiator of radical polymerization. The cluster complex (the metal core and its ligand environment) is retained during copolymerization. The molecular weight characteristics of the copolymers obtained were studied. The double bonds in the cluster monomers mostly retain the properties inherent in their organic analogs.

Hydrolysis of isobutylaluminum aryloxides studied by 1H NMR and quantum chemical methods

AbstractThe results of 1H NMR and quantum chemical studies of hydrolysis of isobutylaluminum aryloxides are presented. According to the data of 1H NMR spectroscopy, the hydrolysis of monomeric diisobutylaluminum aryloxides (2,6-Bu2t—C6H3O)AlBu2i and (2,6-Bu2t,4-Me—C6H2O)AlBu2i occurs selectively at the Al—OAr bond to form the corresponding sterically bulky phenol and polyisobutylaluminoxane. At the molar ratios Al: H2O = 2, the formed sterically bulky phenol reacts slowly with diisobutylaluminum monoaryloxide to form isobutylaluminum diaryloxide. Dimeric aryloxide [(2-But—C6H4O)AlBu2i]2 is not hydrolyzed under similar conditions. The quantum chemical calculations confirmed the experimental results: the hydrolysis at the Al—OAr bond has a lower energy barrier than that at the Al—C bond because of the formation of