Gerhard Luft’s research while affiliated with Technische Universität Darmstadt and other places

Four new donor-functionalized ansa-zirconocenes have been synthesized from the XMeSiCp2ZrCl2 and X2SiCp2ZrCl2 general formula (where X = (CH2)3OEt, C8H4SCH2OMe, and CH2(2-MeO-3-Me-C6H3)). In each of these metallocenes, alkoxy groups are linked by a three-carbon chain to the silicon atom. To study the influence of the functionalized side chains, these metallocenes were activated with methylalumoxane (MAO) and utilized in solution polymerization of ethylene. The molecular weight distributions of the polymers formed show a bimodal shape which can be described as a superposition of two Schultz-Flory distributions, synonymous to at least two different catalytic species. Unimodal polymers with Mw/Mn = 2 were formed with the Me2SiCp2ZrCl2/MAO catalyst system, indicating that the unusual bimodal molecular weight distributions are due to the functionalized side chains tethered to the Si-bridge.

The phase behaviour of mixtures of supercritical propene and a number of polypropenes, which have a similar density but significantly different molecular weights and tacticities, was investigated in a broad range of polymer weight fractions and temperatures at high pressures. The cloud-point pressures were measured optically, using a view cell which was equipped with two windows made of synthetic sapphire and a metal bellows to accurately adjust the pressure. The cloud-point pressures were found in the range from 29 to 37 MPa decreasing with increasing polymer weight fraction and increasing with increasing temperature and polymer molecular weight. The critical weight fraction was found below 2 to 6 wt.-%. Whereas the cloud-point pressures of atactic and syndiotactic samples were high and very similar, the isotactic species exhibit distinctly lower values. The results, extrapolated to lower temperatures, show good agreement with the literature data.

Da nur wenige Daten über das Phasenverhalten von Mischungen aus Propen und Polypropen unter industriellen Polymerisationsbedingungen vorliegen, wurden Untersuchungen mit isotaktischen Polypropenen durchgeführt, die bei gleicher Dichte und ähnlicher Polydispersität stark unterschiedliche gewichtsmittlere Molmassen aufweisen. Es wurden die Trübungsdrücke in Abhängigkeit von der Polymermolmasse, dem Polymeranteil in der Mischung und der Temperatur gemessen. Diese sind wesentlich niedriger als die vergleichbarer Mischungen aus Ethen und Low-Density-Polyethenen oder Ethen/Vinylacetat und Ethen/Vinylacetat-Copolymeren. Only few data for phase behavior of propene and isotactic polypropene under the conditions of the industrial process are known. Therefore, investigations were performed using polypropenes with similar densities and polydispersities but different molecular weights. The pressures at the cloud point were measured in dependence of the polymer molecular weight, of the fraction of the polymer in the mixture, and of the temperature. Cloud point pressures which are drastically lower than that of mixtures of ethylene and low density polyethylenes or ethylene/vinyl acetate and ethylene/vinyl acetat-copolymers were obtained.

The phase behaviour of mixtures of ethylene and polyethylene was studied under pressures up to 200 MPa at temperatures between 383 and 473 K simultaneously by optical and analytical measurements. Three different low density polyethylenes with number average molecular weights of 1100, 19500 and 55000 g/mol were used. In order to show the influence of long chain branching the results were compared with datas published on mixtures of ethylene and linear polyethylenes. It was found that the heterogeneous region extends with rising molecular weight of the polymer and falling temperatures. With branched polyethylenes the critical pressure was lower. The dependency of the critical pressure on the molecular weight and the branching could be expressed by an equation analogous to the relation between the critical temperature and the polymer molecular weight in diluted solutions.

The penetration depths (PDs) of 81 different organic liquids into uncracked dry cement mortar were measured by a suction test at ambient pressure. The physicochemical properties of the liquids (viscosity (η), surface tension (σ), density (ρ), partition coefficient (logP), and molecular volume) were correlated with their penetration depth at normal pressure. It was found that viscosity has the main impact on the penetration. It could be shown by dimensional analysis that the penetration depth at ambient pressure is proportional to the parameter (σρ/η2)1/4. Furthermore, a device to measure the penetration at high pressure up to 50 bar was set up. It was experimentally found that the natural logarithm of the PD at constant time is approximately proportional to the natural logarithm of the applied pressure. A method was elaborated to extrapolate the penetration depth at normal pressure from one single high-pressure measurement. The advantage of this technique is the significantly shorter measurement time for the high-pressure test of 15 min up to 1 h compared to the usual tests at normal pressure which require 72 h.

The influence of highly compressed gases on the melting of polyethylene was investigated for nitrogen, helium and ethylene. The impact of the particle size of the polymer and the heating rate on the melting point were also analysed. The melting points were determined with a high pressure differential thermal analysis (HPDTA) apparatus. These measurements were compared with independent measurements, done by high pressure differential scanning calorimetry (HPDSC), without gas.From this experimental data it was possible to calculate the concentration of the gas in the molten polymer phase based on equilibrium thermodynamics. For high density polyethylene (HDPE), a concentration of nitrogen at the polymer melting point of 10.4–35.7 mL(SATP) g(polymer)−1, in the pressure interval of 65–315 MPa, was calculated.

Pressure relief systems are used to protect pressure vessels and related equipment against situations of excess pressure. In an emergency situation, they should vent sufficient mass to reduce the pressure to a safe level. The effective discharge area of a pressure relief valve is calculated with the theory of flow through convergent-divergent nozzles taking into account a correction factor. The international standard ISO 4121 and that of the American Petroleum Institute API 520 are recommended for sizing. In order to examine the validity of these methods for sizing valves for use at very high pressures, relief experiments should be performed over a wide range of pressures and temperatures. Because of their industrial importance, high pressures of 150–300 MPa, and large reactor capacities of up to 300,000 t/a, the polymerization of ethylene was selected as an example reaction.

In this paper the development and investigation of a new type of immobilized catalyst for the hydroformylation of long-chain alkenes is presented. The catalyst system consisted of the well known metal complex carbonylhydrido-tris-(m-sulfo-triphenylphosphine)-rhodium which was immobilized on activated carbon treated at high temperature. As starting materials 1-hexene, 1-decene, 1-tetradecene, 2-hexene and 2,3-dimethyl-2-butene were used. For all linear α-olefins the same n/iso ratio in the product of 2:1 was determined. The reaction rate decreased with increasing chain length and sterical hindrance of the alkene double bond. All hydroformylation experiments were performed in a stirred semi-batch reactor. Catalyst leaching turned out to be a function of solvent polarity. Using n-heptane as solvent the immobilized catalyst remained stable on the carrier. The activity of the immobilized catalyst decreased compared to the homogeneous catalyst system. Water content was identified to be one of the most significant parameters of the reaction rate.The simulation of experimental data was modelled by a semi-empirical rate law. Within the simulation the reaction scheme consisting of hydroformylation, isomerization and aldol reaction was simultaneously calculated. It was possible to determine the reaction orders of all components, rate constants and the activation energies of all reactions.

Combining dimethylphosphinylethanols HO(R1R2)CCH2PMe2 (1: R1=R2=C6H5; 2: R1=R2=4-OMe–C6H4; 5: R1=R2=4-NMe2–C6H4) with methyl(methoxo)(trimethylphosphine)nickel gave mononuclear methyl(trimethylphosphine)nickel(chelate) compounds 7–9. Ligand 6 (R1=Me, R2=4-OMe–C6H5) afforded a dinuclear methylnickel compound 14. By reacting (TMEDA)lithium-dimethylphosphinylmethanide with ketones OC(R1R2), the dimethylphosphinylethanols HO(R1R2)CCH2PMe2 (3: R1R2=9-fluorenyl; 4: R1=H, R2=C6H5) were synthesized as prechelate ligands. Under otherwise similar conditions, the fluorenyl substituted anion in 3 gave rise to a mononuclear complex 10 which was found to act as a source of trimethylphosphine forming dinuclear 11 and at the same time to act as an acceptor of trimethylphosphine forming pentacoordinate 10·PMe3. Ni(COD)(PMe3)2 was used as a scavenger of PMe3 in converting 8 or 9 to the dinuclear methylnickel compounds 12 and 13, respectively. Modifying the P,O chelating unit of a methyl nickel compound by introducing 2-phosphinylethanolato ligands leads to novel single-component catalysts for ethene oligomerization showing moderate reactivity and thermal stability.

The pressure dependence of the melting point of various polymers including homo- and copolymers (HDPE, LDPE, PP and ethylene vinyl acetate copolymers (EVA)) was investigated under nitrogen atmosphere up to 330 MPa within a high pressure differential thermal analysis cell designed by our group. The properties of the polymers (vinylacetate content, melt flow index, molecular weight, isotactic index, crystallinity, density, and frequency of branching) have been correlated with the change of the melting point under pressure (dTm/dp). It could be shown that the melting point always increases linearly with pressure up to 330 MPa. The pressure dependence was found to be in the range of 11–17 K/(100 MPa). From these results it is possible to approximate dTm/dp using the enthalpy of fusion of the polymers at ambient pressure.