Velocity measurements on a polypropylene melt during extrusion through a flat coat‐hanger die

An experimental investigation of various flow regimes observed during the extrusion of a polypropylene melt through a flat coat‐hanger die by laser‐Doppler velocimetry (LDV) is presented. LDV measurements of the velocity profiles across the gap of the die at various locations along the die reveal three different extrusion regimes. At small wall shear stresses, the velocity profiles can be fitted by symmetrical curves with the velocities becoming zero at the die walls. These profiles are not uniformly distributed along the die. An increase of the wall shear stress reveals a second flow regime characterized by a uniform distribution of the velocity profiles along the die. As the wall shear stress is increased even further, a third flow regime characterized by wall slip on the glass windows is observed. This flow regime is systematically characterized by measurements of the slip velocities at various temperatures and throughputs. The maximum velocities along the die are taken to assess the uniformity of flow which decisively influences the thickness of the extruded film. By measuring velocity profiles, at different throughput, and temperatures, the conditions for constant velocities along the die were determined. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers     

Methacrylated calix[4]arene phosphonic acids as functionalized crosslinker for radical polymerization

We describe the synthesis of 5,11,17,23‐tetra‐tert‐butyl‐25,27‐dioxypropylphosphonic acid‐26,28‐dimethacryloyloxy‐calix [4]arene and 5,11,17,23‐tetra‐tert‐butyl‐25‐oxypropylphosphonic acid‐27‐hydroxy‐26,28‐dimethacryloyloxy‐calix[4]arene starting from para‐tert‐butyl‐calix[4]arene. The complete reaction was proved by matrix‐assisted laser desorption ionization time of flight mass spectrometry and nuclear magnetic resonance spectroscopy. The influence of these compounds on the kinetics of the radical polymerization of methyl methacrylate was shown by dilatometry. Furthermore, the adhesive properties of dental adhesives containing these calix[4]arene derivatives were investigated. Copyright © 2012 Society of Chemical Industry     

Hydroxyl‐functional polyurethanes and polyesters: synthesis,properties and potential biomedical application

This mini review gives an overview of the synthesis of polyurethanes and polyesters with pendant hydroxyl groups performed mainly in our group. Significant for the synthesis of most of these polymers with hydroxyl‐functional side groups is that no protection groups are needed. This is realised either by generating the OH group during polymer synthesis—demonstrated by the preparation of hydroxyl‐functional polyurethanes from dicarbonate monomers and diamines—or by using catalysts which discriminate between primary and secondary OH groups—demonstrated by the synthesis of hydroxyl‐functional polyesters based on malic acid using scandium triflate as catalyst. In addition, the potential of carbonate couplers for the synthesis of multifunctional polyurethane is presented. The application of such multifunctional polyurethanes as antimicrobial polymers and coatings is briefly discussed. Copyright © 2012 Society of Chemical Industry     

Flow behavior of polypropylenes with different molecular structures in a coat‐hanger die

An experimental investigation of the flow behavior of three polypropylene melts with different molecular structures during extrusion through a coat‐hanger die is presented. Two linear and one long‐chain branched material, rheologically characterized in shear and elongation, were investigated. Using laser–Doppler velocimeter measurements of the velocity profiles across the gap height were performed at five various locations along the die. The uniformity of the velocity distribution along the die has been assessed using the maximum velocities v₀ of the corresponding velocity profiles across the gap. The velocity distribution along the die changes with throughput and temperature. Regarding the rheological properties, it was found that the power‐law index of the viscosity as a function of shear rate has a decisive influence on the uniformity of flow but that the pronounced strain hardening in elongation typical of the long‐chain branched polypropylene is not reflected by the velocity distribution along the die. POLYM. ENG. SCI., 2012. © 2012 Society of Plastics Engineers     

Influence of a compatibilizer on the morphology development in polymer blends under elongation

Compatibilization is the modification of the interface in immiscible polymer blends in order to refine and stabilize their phase structure. The presence of a compatibilizer at the interface markedly affects the deformation behaviour of the dispersed droplets during and after cessation of flow. In this work the morphology development in blends of polystyrene and linear low-density polyethylene compatibilized with styrene-butadiene-styrene triblock copolymer during and after uniaxial elongation was investigated by means of electron microscopy and small-angle X-ray scattering. The incorporation of only 1 wt.-% of the compatibilizer led to a pronounced increase of the stationary elongational viscosity of the blend. It was found, that at moderate capillary number (Ca ≈ Ca_CR) the compatibilizer stabilises the droplets against break-ups during the flow. When Ca >> Ca_CR no differences in the deformation of uncompatibilized and compatibilized droplets were observed. After cessation of the flow, the presence of the compatibilizer prevented the droplet break-up and supported and accelerated the shape recovery of the elongated particles.     

Selective Hydrogenation of Biomass-Derived Succinic Acid: Reaction Network and Kinetics

The conversion of bio-based succinic acid (SA) to the value-added chemicals 1,4-butanediol (BDO), γ-butyrolactone (GBL), and tetrahydrofuran (THF) can replace the corresponding petrochemical production routes to achieve a sustainable process. The reaction network for aqueous-phase catalytic hydrogenation of succinic acid over a supported Re-Pd catalyst was identified and the reaction kinetics was determined. With the developed kinetic model, the composition of the product mixture regarding the desired products (BDO, GBL, THF) can be described as a function of educt concentration, temperature, and pressure. The maximum BDO yield was achieved at high pressure and low temperature, while low pressure and high temperature favored GBL and THF production.     

Novel Positive Allosteric Modulators of µ Opioid Receptor—Insight from In Silico and In Vivo Studies

Opioids are the drugs of choice in severe pain management. Unfortunately, their use involves serious, potentially lethal side effects. Therefore, efforts in opioid drug design turn toward safer and more effective mechanisms, including allosteric modulation. In this study, molecular dynamics simulations in silico and ‘writhing’ tests in vivo were used to characterize potential allosteric mechanism of two previously reported compounds. The results suggest that investigated compounds bind to μ opioid receptor in an allosteric site, augmenting action of morphine at subeffective doses, and exerting antinociceptive effect alone at higher doses. Detailed analysis of in silico calculations suggests that first of the compounds behaves more like allosteric agonist, while the second compound acts mainly as a positive allosteric modulator.     

Coupling of N2O Decomposition and Ethylbenzene Dehydrogenation over γ-Al2O3-Supported Transition Metal Oxide Catalysts

Transition metal (Cr, Cu, Fe, Co and Ni) oxides supported on -alumina were characterized with respect to their textural parameters and reducibility and used as catalysts in decomposition of nitrous oxide and ethylbenzene (EB) dehydrogenation as well as coupling of both processes. High activity of -Al₂O₃ in N₂O decomposition coupled with EB dehydrogenation has been found. An increase in EB and N₂O conversion was observed when transition-metal-containing catalysts were used. The activity of catalysts depended on their reducibility. Maximum N₂O efficiency was observed for the Cr/-Al₂O₃ sample, whereas -Al₂O₃-supported Cu and Fe oxide systems showed about 50% efficiency of N₂O in the reaction. An influence of the molar ratio of N₂O/EB on activity and selectivity of the catalysts was found. An excess of N₂O resulted in an increase in CO₂ formation at nearly constant styrene yield.     

Single amino acid substitutions can further increase the stability of a thermophilic L-lactate dehydrogenase

Lactate dehydrogenases are of considerable interest as stereospecificcatalysts in the chemical preparation of enantiomerically pure-hydroxyacid synthons. For such applications in synthetic organicchemistry it would be desirable to have enzymes which tolerateelevated temperatures for prolonged reaction times, to increaseproductivity and to extend then applicability to poor substrates.Here, two examples are reported of significant thermostabilizations,induced by sitedirected mutagenesis, of an already thermostableprotein, the L-lactate dehydrogenase (EC 1.1.1.27 [EC] , 35 kDa permonomer subunit) from Bacillus stearothermophilus. Thermal inactivationof this enzyme is accompanied by irreversible unfolding of thenative protein structure. The replacement of Argl71 by Tyr stabilizesthe enzyme against thermal inactivation and unfolding. Thisstabilizing effect appears to be based on improved interactionsbetween the subunits in the core of the active dimeric or tetramericforms of the enzyme. The thermal stability of L-lactate dehydrogenasevariants with an active site Arg residue, either in the 171(wild-type) or in the 102 position, is further increased bysulfate ions. The two stabilizing effects are additive, as foundfor the Argl71Tyr/ Gln1O2Arg double mutant, for which the stabilityof the protein in 100 mM sulfate solution reaches that of L-lactatedehydrogenases from extreme thermophiles. All mutant proteinsretain significant catalytic activity, both in the presenceand absence of stnhilfoing salts, and are viable catalysts inpreparative scale reactions.