Alexander Rau

Synthesis and application in high-pressure polymerization of a titanium complex with a linked cyclopentadienyl-phenoxide ligand

Abstract The ansa half-sandwich complex [η 5 :η 1 -C 5 H 4 -C(CH 3 ) 2 -2-C 6 H 4 O]TiCl 2 ( 1 ) has been prepared using two different ways, a ‘one-pot’ synthesis and a synthesis via thermolysis of the Ti trichloride precursor [η 5 -C 5 H 4 -C(CH 3 ) 2 -2-C 6 H 4 OCH 3 ]TiCl 3 ( 3 ). When activated with methylaluminoxane ( 4 ) or the cocatalyst system triisobutyl aluminum/[Me 2 PhNH] + [B(C 6 F 5 ) 4 ] − ( 5 ), complex 1 could be used as a catalyst in high-pressure, high-temperature polymerization. The productivity of the catalyst system 1 / 4 in high-pressure polymerization of ethene is 400 t polymer mol −1 Ti, while the productivity of catalyst system 1 / 5 is only 6 t polymer mol −1 Ti. In ethene/1-hexene copolymerizations productivity and molecular weights decrease with increasing 1-hexene in the feed. The polymerization results were discussed and compared to results of high-pressure polymerization with the catalyst system Me 2 Si[IndH 4 ] 2 ZrCl 2 / 4 .

Influence of aluminium alkyl compounds on the high-pressure polymerization of ethylene with ternary metallocene-based catalysts. Investigation of chain transfer to the aluminium

The influence of aluminium alkyl compounds on metallocene-catalyzed high pressure polymerizations of ethylene has been investigated at 150 MPa and 180°C in a continuously operated autoclave. The catalysts were based on the metallocenes bis(cyclopentadienyl)zirconium dichloride (Cp2ZrCl2) and diphenylmethylene (cyclopentadienylfluorenyl)zirconium dichloride (Ph2C-(CpFlu)ZrCl2), which were preactivated outside the reactor with triisobutylaluminium (TiBA) and N,N-dimethylanilinium tetrakis(pentafluorophenyl)borate (DMAP, [PhNHMe2][B(C6F5)4]). The concentrations of triisobutylaluminium (TiBA) and triethylaluminium (TEA) in the reactor were varied over a wide range, using a separate dosing for these two aluminium alkyl compounds. Productivity and polymer properties strongly depended on the type and the concentration of the aluminium alkyl compound used. Highest productivities and molecular weights were obtained with low concentrations of TiBA in the reactor. Up to a concentration of 30 molppm Al in the reactor, unimodal polymers were formed with Mw/Mn between 2 and 3. With higher aluminium concentrations the products formed contained small amounts of waxes, due to oligomerization catalyzed by the aluminium alkyl compounds. The molecular weight distributions (MWDs) of these products could be described as a superimposition of two Schulz-Zimm distributions. All MWDs were analyzed with regard to the amount of waxes produced by ethylene oligomerization and with regard to the influence of chain transfer reactions to the aluminium. The rate constants of chain transfer to aluminium, in relation to the rate constants of insertion of ethylene, were estimated.

Ternary metallocene catalyst systems based on metallocene dichlorides and AlBu3i/[PhNMe2H][B(C6F5)4]: NMR investigations of the influence of Al/Zr ratios on alkylation and on formation of the precursor of the active metallocene species

Abstract The formation of the precursors of the polymerization-active species of the metallocene dichlorides Cp2ZrCl2 and Ph2C(CpFlu)ZrCl2 by successive reaction with AlBu3i and [PhNMe2H][B(C6F5)4] was investigated by means of NMR spectroscopy. More than two equivalents of AlBu3i are required for total conversion of the metallocene dichlorides in the first step. The reaction of Ph2C(CpFlu)ZrCl2 with AlBu3i leads exclusively to the mono-iso-butyl complex Ph2C(CpFlu)ZrClBui, independent of the surplus AlBu3i used, whereas in the case of Cp2ZrCl2 a series of metallocene products are observed, depending on the Al/Zr ratio used. When this ratio was increased to above 10, the reaction could be exclusively directed to form the dimer metallocene complex [Cp2ZrH2·AlBu3i]2. The reaction of [PhNMe2H][B(C6F5)4] with metallocene/aluminium alkyl mixtures prepared with 10, 20, 50 and 100 equivalents of AlBu3i leads to the precipitation of an oily liquid, which contains resulting cationic metallocene complexes. These liquid phases can be purified by extraction and subsequently used for NMR measurements. With one exception, mixtures of two or three different cationic metallocene products are obtained, depending on the Al/Zr ratio and on the metallocene ligand used. An Al/Zr ratio of 100 the reaction of the Ph2C(CpFlu)ZrCl2/AlBu3i mixture with [PhNMe2H][B(C6F5)4] exclusively leads to the cationic heterodinuclear metallocene complex [Ph2C(CpFlu)Zr-μ-H-μ-(C4H7)-AlBu2i]+, a novel type of allyl-bridged cation, which was characterized by NMR data. None of the reactions of metallocene dichloride/aluminium alkyl mixtures with [PhNMe2H][B(C6F5)4] lead to the degradation of [B(C6F5)4]−, whereas in the absence of metallocenes AlBu3i reacts with [PhNMe2H][B(C6F5)4] to give AlBu3−xi(C6F5)x compounds. Based on these results and with additional information from the literature a mechanism is proposed to explain the formation of [Ph2C(CpFlu)Zr-μ-H-μ-(C4H7)-AlBu2i]+.

Investigations on ternary metallocene-based catalyst systems

The influence of the cocatalyst triisobutyl aluminium (TiBA) on the two step reaction of the ternary activation of the metallocene precursor Ph 2 C(CpFlu)ZrCl 2 with TiBA and the activator N,N-dimethylanilinium-tetrakis(pentafluorophenyl)borat (DMAB) was investigated by means of NMR spectroscopy. More than 5 equivalents of TiBA are required for a total conversion of Ph 2 C(CpFlu)ZrCl 2 . The reaction exclusiveley leads to the monoalkyl complex Ph 2 C(CpFlu)ZrClBu 1 independent of the Al / Zr ratio. The reaction of the Ph 2 C(CpFlu)ZrCl 2 / TiBA mixtures, using 10, 20 and 50 equivalents of TiBA with DMAB, generates two cationic metallocene species. Using 100 equivalents of TiBA exclusiveley leads to the formation of the cationic heterodinuclear metallocene complex [Ph 2 C(CpFlu)Zr-(μ-H)-(μ-C 4 H 7 )-AlBu 1 2 ] + . In no case was the degradation or complexation of [B(C 6 F 5 ) 4 ] - detected, whereas the direct reaction between TiBA and DMAB gives AlBu 1 3-x (C 6 F 5 ) x compounds. A mechanism was postulated to explain the formation of [Ph2C(CpFlu)Zr-(μ-H)-(μ-C 4 H 7 )-AlBu 1 2 ] + . The catalyst system Ph 2 C(CpFlu)ZrCl 2 / TiBA / DMAB was used for continuous high pressure polymerizations of ethylene at 150 MPa and 180 °C. To investigate the influence of additional TiBA and triethyl aluminium (TEA) in the reactor, their concentrations were varied over a wide range. Highest productivities and molecular weights were obtained with low concentrations of TiBA in the reactor. Up to a concentration of 30 molppm Al in the reactor, unimodal polymers were formed with Mw / Mn between 2 and 3. With higher aluminium concentrations, the products formed contained small amounts of waxes. This was due to oligomerization catalyzed by the aluminium alkyl compounds. Using the Schulz-Zimm distribution all MWDs were analyzed with regard to the amount of waxes produced by ethylene oligomerization and with regard to the influence of chain transfer reactions to the aluminium. The rate constants of chain transfer to aluminium in relation to the rate constants of insertion of ethylene were estimated.

Kinetic Investigations of the Metallocene – Catalyzed Polymerization of Ethylene at High Pressure

Metallocene catalysts are already used for the industrial high-pressure polymerization of ethylene. The products form this process show a small molecular weight distribution and a uniform incorporation of the comonomer. Excellent properties, suitable for the industrial use of the polymers results from this special molecular structure. The aim of this experimental work is to evaluate the kinetic parameters numerically, that is the pre-exponential factor, the activation energy and the activation volume, which describes the pressure dependence. Therefore, polymerization tests are performed varying the concentration of ethylene and catalyst, temperature and pressure.

Ternary Metallocene Based Catalysts in High Temperature, High Pressure Polymerization

High pressure copolymerizations of ethene and 1-hexene were performed by use of a ternary catalyst system based on Me2Si[Ind]2ZrCl2, A1(iBU)3 and [PhNHMe2][B(C6F5)4]. The productivity depends strongly on the molar ratio of [Al]/[Zr] used. With small amounts of 1-hexene in the feed a rate enhancement of the ethene polymerization rate was observed. Incorporation of 1-hexene in the polymer was studied as well as the influence of 1-hexene on polymer density.

Influence of Ligands on the Deactivation of Group IV Metallocene Catalysts in the High-Temperature Polymerization of Ethene

Ethene polymerizations were performed using catalyst Systems based on different types of zirconocene dichlorides and Al(iBu)3/ [PhNHMe2]*[B(C6F5)4] at temperatures of 100 to 140 °C and pressures of 20 to 70 bar. The starting polymerization rate Rp0 of the (nBu-Cp)2ZrCl2-based catalyst increases linearly with increasing catalyst concentration. The same catalyst showed a second-order dependency of Rp0 on the ethene concentration, Rp0 ∼ [ethene]2.0 . The rate time profiles showed a rapid decay in activity, which could be described with first-order deactivation reactions regarding the concentration of active sites. The rate constants of deactivation kd were determined for a series of seven different metallocene catalysts. The half-lives resulting from kd were used to compare the stability of the metallocene catalysts with different ligand Systems.