A. N. Panin

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.

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.

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.

Mechanochemical synthesis of zirconium and hafnium phenoxyimine complexes L2MCl2 (L = N-(3,5-di-tert-butylsalicylidene)-2,3,5,6-tetrafluoroanilinate anion) and their catalytic properties in ethylene polymerization

A new method for preparation of zirconium and hafnium phenoxyimine complexes L2MCl2 (L is N-(3,5-di-tert-butylsalicylidene)-2,3,5,6-tetrafluoroanilinate anion, M = Zr, Hf) by the solid state interaction of N-(3,5-di-tert-butylsalicylidene)-2,3,5,6-tetrafluoroaniline, the corresponding metal chlorides, and sodium hydride under mechanical activation followed by heating of the activated mixture was developed. The obtained complexes have a high catalytic activity in the reaction of ethylene polymerization.