bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polymorphism and structure in different kinds of liquid crystal polymers and copolymers
Authors: Hardouin F. 
Published: March 2011

AbstractWe report a short outline of chain‐conformation informations obtained by small angle neutron scattering (SANS) studies of different kinds of Liquid Crystalline Polymers (LCPs). We conclude that in the nematic phase the prolate shape of the chains are directly connected to the orientational order and the magnitude of the chain extension strongly depends on molecular parameters relative to the coupling mesogen‐chain. The behavior is markedly different when the backbone anisotropy is oblate shape due to the chain confinement between the smectic layers.
Smectic liquid single crystal elastomers
Authors: Finkelmann H. , Benné J. , Semmler K. 
Published: March 2011

AbstractIn the liquid crystalline (I.c.) state the backbone of l.c‐polymers has to adapt an anisotropic conformation that is consistent with the I.c.‐phase structure. For macroscopically uniformly aligned samples this anisotropic backbone conformation can be obtained by applying a suitable mechanical field on chemically crosslinked I.c‐polymers. Introducing the network anisotropy a priori by synthesis, stable macroscopically aligned I.c.‐networks can be realized. We have called these networks Liquid Single Crystal Elastomers (LSCE) because their physical properties resemble that of organic or inorganic single crystals.
Side chain liquid crystalline polymers: Electric field effects and nonlinear properties
Authors: Gonin Dominique , Guichard Bertrand , Noël Claudine , Kajzar François 
Published: March 2011

AbstractSide chain liquid crystalline polymers offer unique advantages as a new class of organic materials with potential for nonlinear optical response. Synthesis of a number of cyanobiphenyl‐based side chain polymers was carried out employing the concept of having the cyanobiphenyl species serve concomitantly as both the linear optical chromophore and the mesogenic moiety in the polymer. The thermal behavior of these polymers was studied by DSC, optical microscopy and X‐ray diffraction. Thin polymeric films were spin coated and electric field poling measurements were carried out as a function of temperature. The second harmonic (SH) coefficients d33 and d31 were measured by Maker fringe analysis and compared with the values predicted by molecular statistical models. The results showed that one can gain in net polar ordering by starting with a liquid crystalline system. The enhancement in d33 when < P<2 > = 0,6 was found to be a factor of 2,3‐3,3 over the isotropic case ( P<2 > = 0). The relaxation process was investigated. Both the presence of liquid crystal character in the material and the temperature at which the films were stored below Tg appeared important in determining the thermal stability of the SH coefficients.
α‐Olefin polymerization by various alumoxanes containing isobutyl group and metallocene
Authors: Kurokawa Hideki , Sugano Toshihiko 
Published: March 2011

AbstractEthylene or propylene polymerization was carried out by use of Me2Si(H4Ind)2ZrCl2 and alumoxanes containing isobutyl group. Polymerization activity of ethylene decreased with an increase of the isobutyl group content. On the contrary, the alumoxane having isobutyl group content of about 50% gave a maximum activity for propylene polymerization.
Mao based catalysts for syndiotactic polystyrene (sPS)
Authors: Campbell Richard E. , Newman Thomas H. , Malanga Michael T. 
Published: March 2011

AbstractSeveral non‐metallocene (Ti, Zr) and substituted mono‐Cp titanium metallocenes have been tested in the presence of methylalumoxane (MAO) as catalyst for syndiospecific polymerization of styrene. Effect of substitutions on the titanium and Cp ligand, molar ratio of Al/Ti, TMA and temperature on activity, Mwt. and % sPS were studied. CpTi(OiPr)3 gives a less active catalyst than Cp*Ti(OiPr)3 and the resulting sPS is less stereoregular and of lower molecular weight.
Copolymerization of poly(propylene) macromonomer and ethylene with metallocene catalysts
Authors: Shiono Takeshi , Moriki Yuji , Soga Kazuo 
Published: March 2011

AbstractCopolymerization of ethylene and poly(propylene) macromonomer(PPM) with Mn⇋710 was conducted with the (t‐butylamido)dimethyl(tetramethyl‐η5‐cyclopentadienyl)silanetitanium dichloride(CGC‐Ti), ethylenebis(tetrahydroindenyl)zirconium dichloride(Et[IndH4]2ZrCl2), bis(cyclopentadienyl)zirconium dichloride(Cp2ZrCl2) and bis(cyclopentadienyl)titanium dichloride(Cp2TiCl2) catalysts using methylaluminoxane as cocatalyst. From the detail analysis of resulting copolymers by DSC, IR and 13C NMR, it was proved that PPM is copolymerized with ethylene to give poly(ethylene‐co‐PPM). The ability of incorporating PPM in the copolymer was found to increase in the following order: Cp2ZrCl2 «Cp2TiCl2 < Et[IndH4]2ZrCl2 «CGC‐Ti.
Mixed cocatalyst systems in metallocene ethylene polymerization
Authors: Michiels Wilfried , Muñoz‐Escalona Antonio 
Published: March 2011

AbstractThe effect of the cocatalysts resulting from mixing AIR3 (R = Me (TEA), Et (TEA) and iBu (TIBA)), and B(C6F5)3 with MAO at different molar ratios on ethylene polymerization activities and on the molecular weight and microstructures of the resulting polymers using the catalyst Cp2ZrCl2 was explored. It has been observed that activities increase at low TMA concentrations with increasing TMA/MAO ratios, reaching a maximum at the TMA/MAO ratio of 0.3‐0.5. A decrease of the polymerization activities was observed at higher TMA/MAO ratios. Addition of TEA or TIBA to the MAO brings about a decrease in the polymerization activities, being the effect stronger for TEA. The use of B(C6F5)3 in the mixed cocatalyst systems leads to higher activities stabilizing also the active centers. The molecular weights of the polyethylenes follow the same trend, i.e. they decrease with increasing AIR3/MAO ratios (TIBA, with bulky R, gives the highest molecular weight because of the reduction of chain transfer reactions to the aluminium compound) but they are little affected by the presence of B(C6F5)3.
Microstructure of poly(cycloolefins) produced by metallocene/methylaluminoxane (mao) catalysts
Authors: Arndt Michael , Kaminsky Walter 
Published: March 2011

Abstract[1]: The microstructures of poly(norbornenes) and poly‐(cyclopentenes) produced by metallocene/mao catalysts are investigated. Hydrooligomerizations have been performed and the products were identified by NMR spectroscopy. Using these hydrooligomers as models assignments for CPMAS spectra of the polymers were made. Regio‐ and stereoselectivity of the polymerization of cyclic monomers are discussed and compared to those observed in propene polymerization.
In search of the plastic enzyme
Authors: Guillet James E. , Burke Nicholas A. D. , Nowakowska Maria , Reese Howard , Gravett David M. 
Published: March 2011

AbstractPhotozymes are novel polyelectrolytes made from mixtures of hydrophobic and hydrophilic comonomers. They often contain a relatively high concentration of bound chromophores as photon harvesting or antenna groups, which transport excitation energy to organic substrates located in the interior of the macromolecular coil in aqueous solution. Previous studies have shown that the photocatalytic behavior of these polymers has many similarities to natural enzymes which carry out thermal reactions in biological systems. Mechanistic studies of four photozyme reactions are discussed: (1) the oxidation of perylene to perylenequinones; (2) the dehalogenation of hexachloro‐ and pentachlorobenzene; (3) the high‐yield synthesis of Vitamin D; and (4) the selective photolysis of aliphatic and aromatic ketones.
Preparation of elastomeric polypropylene using metallocene catalysts: Catalyst design criteria and mechanisms for propagation
Authors: Gauthier William J. , Collins Scott 
Published: March 2011

AbstractA series of unsymmetrical metallocene catalysts were prepared and used to polymerize propylene under a variety of conditions using methylaluminoxane as a cocatalyst. Zirconium and hafnium‐based catalysts were more active and more importantly, much more stable at conventional polymerization temperatures than titanium catalysts. By adjusting experimental conditions, it is possible to vary both the molecular weight of the polymer and also the degree of crystallinity. These properties significantly impact on the tensile properties of elastomeric poly(propylene) (ELPP) in a predictable manner. The microstructure of ELPP was characterized by 13C NMR spectroscopy and the pentad distributions were analyzed using several statistical models for propagation. This work has demonstrated that the microstructure of ELPP is probably not that of an isotactic‐atactic block copolymer.
Polymers with indan units
Authors: Nuyken Oskar , Maier Gerhard , Leitner Michael , Yang Dazhong , Wolf Martin 
Published: March 2011

AbstractCationic polymerisation of 1, 4‐diisopropenyl benzene, 1, 4‐(2‐chloro‐isopropyl)benzene and related compounds yields soluble polymers with repeating units of indan.High performance polymers with indan units are available via nucleophilic substitution of halogenated aromatic monomers containing a central indan element, which are synthesized from 1, 1, 3‐trimethyl‐3‐phenylindan via Friedel‐Crafts‐reaction with corresponding halogenated acyl‐ and sulfonyl chlorides.
Mesomorphic properties and sans conformational study in different liquid crystalline polymers
Authors: Hardouin F. 
Published: March 2011

AbstractWe report an overview about chain‐conformation informations given by small angle neutron scattering (SANS) studies of different kinds of Liquid Crystalline Polymers. We conclude that in the prolate nematic phase the chains are directly connected to the orientational order and the chain extension strongly depends on microscopic considerations concerning the coupling mesogen‐chain. The behavior is markedly different when the backbone anisotropy is oblate because the chains are hence affected by the smectic layering order (even at the scale of fluctuations in a high temperature nematic phase). In this latter case, since the chains are more or less confined in a 2D Gausssian geometry, they locally do not follow the director and the chain anisotropy mainly depends on the strength of the smectic layering.
Nanoscopic supermolecules with linear‐dendritic architecture: Their preparation and their supramolecular behavior
Authors: Frechet Jean M. J. , Gitsov Ivan 
Published: March 2011

AbstractThe design, synthesis, and properties of supermolecules consisting of well defined assemblies of linear and globular macromolecules is studied. Therefore, several families of hybrid block polymers based on polyether dendrimers linked to well‐defined blocks of polyethylene oxide, polyethylene glycol, polyester, or polystyrene have been prepared. The unique topological macromolecules that result from the assembly of such components having different shapes and internal densities can assemble in highly stable supramolecular micelles whose characteristics vary as a function of the medium. The hybrid macromolecules are usually prepared by the nucleophilic displacement of a reactive functionality located at the focal point of a convergent polyether dendrimer, with a nucleophilic anion located at one or both chain ends of a linear polymer. Alternately, the focal point of the dendrimer may be used to attach a polymerizable vinyl group affording a dendritic macromonomer that may be used to create variety of copolymers. Finally, the focal point of the convergent dendrimer may serve as an initiator in the polymerization of a linear chain thereby affording the hybrid linear‐dendritic entity. In the latter case the unique microenvironment provided by the dendrimer is useful in the prevention of undesirable side‐reactions during growth of the linear block. This demonstrates that the differences between the globular and linear fragments of these unique molecules can be used to design nanoscale reactors that perform functions not normally achieved with small molecules. The very unusual solution properties of the dendritic‐linear supermolecules are a direct result of the forced combination of their dissimilar building blocks.
Multifunctional bioerodible/biodegradable polymeric materials
Authors: Chiellini Emo , Solaro Roberto 
Published: March 2011

AbstractAs a part of our continuing interest in the preparation of multifunctional polymeric materials and evaluation of their potential in biomedical and environmental field, a survey on new polymeric systems susceptible to bioerosion and/or biodegradation attack is presented. In particular attention has been focused on the preparation and characterization of the following classes of polymeric materials: 1) hydroxyl‐containing polyesters; 2) functionalized cyclodextrins; 3) hydrophilic polymers containing carboxylic groups; 4) hydrogels for the release of phytodrugs; 5) hybrid polymeric materials; 6) synthetic and semisynthetic polyfunctional polymeric materials for the removal of uremic toxins. A few examples of the use of these polymers in the controlled release of drugs and as coadjuvants in the chronic renal failure treatment will be also presented.
Synthesis and electro‐optical properties of some ferroelectric liquid crystalline polymers
Authors: Hsu Chain‐Shu , Shih Li‐Jen , Hsiue Ging‐Ho 
Published: March 2011

AbstractThe synthesis and characterization of several series of ferroelectric side‐chain polymers were presented. Differential scanning calorimetry, optical polarizing microscopy and X‐ray diffraction measurement were used to determine their thermal transitions and analyze their anisotropic textures. The influence of polymer backbones, flexible spacers, mesogenic cores as well as chiral end groups on the mesomorphic properties of the polymers was discussed. Furthermore, the dielectric relaxation properties of the obtained polymers were also evaluated.
Rheological investigation of starch polysaccharide gelation
Authors: Vorwerg Waltraud , Radosta Sylvia 
Published: March 2011

AbstractSmall‐amplitude dynamic measurements of aqueous starch polysaccharide solutions are performed by a Bohlin controlled‐stress rheometer with air bearing. Three classes of starch polysaccharides–native starches, fractions of starches and hydrolysed starches–are compared in their molecular composition and rheological properties during and after the gelation process. Viscoelastic properties of solutions and gels are recorded in dependence on temperature and time, yielding storage and loss moduli during and after sol‐gel transition. Hot concentrated aqueous solutions are cooled down from 90 °C to 5 °C at a rate of 1 °C/min. Measurements are carried out at 0,1 Hz and 5% strain amplitude deformation. The typical course of the moduli of gelling starch polysaccharide solutions shows a liquid‐like behavior (G” > G') in the upper temperature level between 60 and 90 °C, a jumpwise increase with ensuing intersection of G' and G” below 60 °C and a solid‐like behavior (G' > G”) at lower temperatures with a slightly in time growing storage modulus. Storage and loss moduli depend on molecular composition and concentration of the substance. The process of starch polysaccharide aggregation is discussed with regard to theories of physical gelation by Ross‐Murphy and Winter.
Polyglucane derivatives with regular substituent distribution
Authors: Klemm Dieter , Heinze Thomas , Stein Armin , Liebert Tim 
Published: March 2011

Abstract6‐O‐trialkylsilyl celluloses, 2,3‐O‐carboxymethylcelluloses, cellulose‐3‐O‐sulfate, and carboxymethylcellulose block copolymers were synthesized by regioselective functionalization of cellulose and of soluble cellulose intermediates like silyl and methoxy‐substituted trityl ethers as well as formates and trifluoroacetates. The preparation and structure characterization (NMR, FTIR, HPLC after chain degradation) of those polyglucane derivatives with regular substituent distribution is of importance to design self‐assembly systems and supramolecular structures (liquid‐crystalline media, ultrathin films, recognition and bioactive materials).
Defined carrageenan derivatives as angiogenesis inhibitors
Authors: Paper Dietrich H. , Vogl Horst , Franz G. , Hoffman Richard 
Published: March 2011

AbstractThree carrageenans derived from red algae and three partially modified carrageenans were tested for their ability to inhibit the formation of new blood capillaries on the chorionallantois membrane of the hen egg. It could be clearly demonstrated that they were better angiogenesis inhibitors than the standard compound suramin.
Trends in non‐polluting organic surface coatings chemistry
Authors: Mezger T. 
Published: March 2011

AbstractPaint application is a sector of human activity, where the common use according to product determination by the end user or small craftmans business contributes most obviously to environment pollution, In first instance of course by solvent evaporation.There is a steadily increasing pressure by governmental authorities on the plant industry to reduce solvent emission from its products.At the same time, more integral approaches of environmental impact assessments ‐ so called life cycle analysis ‐ become more and more important.The paint industry answers these challenges by development of new types of coatings, which mainly means new types of binder polymers and new types of crosslink chemistry.Advances in the understanding of polymer physical chemistry as well as the advent of new synthesis concepts lead to a number of emerging technologies expected to contribute significantly to reduction of pollution by paint application.While in industrial paint application end‐of‐the‐pipe technology is still economically favourably competing with the advanced paint chemistry concepts (e.g. high‐solids, waterborne, UV‐curing, electrocoating, powder coating and supercritical CO2‐application), the situation in the large sector of end‐user and craftsman application of paint is much more difficult, at least in the sector of high performance and particularly high gloss coatings. End‐of‐pipe‐technology is unapplicable and, on the other hand, degrees of freedom in application equipment and curing conditions are limited. Furthermore, labour safety requirement further restrict the scope of applicable new chemistry.
Einige wesentliche Trends bei der Verarbeitung der thermoplastischen (Massen‐) Kunststoffe
Authors: Menges G. 
Published: March 2011

AbstractThe major application of plastics has to obey strong economical restrictions. By this reason users are carefully selecting new machinery. Later‐on high standards in user‐friendly handling and maintenance in high quality of the machinery is required. These wishes are fulfilled by all machinery suppliers worldwide, which are producing in bigger quantities. The technological progress, too follows these rules. Absolutely new technologies are not to see in the fields of mass production, especially with thermoplastic materials and commodities. The development of resin follows, too, the same rules and one can feel a concentration to fewer materials. The most preferred material seems to become polypropylene. One reason for this tendency bases on recycling necessities.
Directed polymer synthesis for industrial application
Authors: Höcker Hartwig 
Published: March 2011

AbstractIn the present survey the limitations for the industrial application of polymer syntheses are discussed as well as the directions, syntheses may go. As particular examples the living anionic polymerization and the respective ring‐opening polymerization and copolymerization are discussed.Under the aspect of future developments some examples of biotechnological polymerization and particular features of biopolymers are given
Conformation and dynamics of fibrous and membrane proteins as revealed by high‐resolution solid‐state nuclear magnetic resonance
Authors: Saitǒ Hazime , Tuzi Satoru , Nishimura Katsuyuki , Fukutani Akira , Naito Akira 
Published: March 2011

AbstractWe examined conformation and dynamics of a variety of fibrous and membrane proteins by means of the conformation‐dependent displacements of 13C nuclear magnetic resonance (NMR) chemical shifts and their relaxation parameters, respectively, as recorded by high‐resolution solid‐state 13C NMR. Determination of three‐dimensional structure of atomic resolution is also briefly described for a simple peptide on the basis of precise measurements of interatomic distances.
Conformation and dynamics of polymer chains in condensed systems
Authors: Kotaka Tadao , Adachi Keiichiro 
Published: March 2011

AbstractA Stockmayer's type‐A chain such as cis‐polyisoprene (PI) having dipole components parallel to the chain contour exhibits slow dielectric response, reflecting fluctuation of its end‐to‐end vector (dielectric normal modes). This article reviews our own work on dielectric spectroscopy for studying dynamics and conformational properties of probe PI chains in binary blends with PI or polybutadiene (PB) that does not exhibit normal modes. Through such studies we were able to see the crossover of the probe‐chain dynamics from Rouse behaviour in low‐molecular‐weight (lmw) matrices to pure reptation behaviour in high‐molecular‐weight (hmw) matrices. We were also able to confirm experimentally Flory's earlier prediction on excluded volumes in dilute blends of hmw probe chains in lmw matrices, for which a proof has never been given before.
Recent developments and future trends in injection molding technology
Authors: Takahashi Hideroh 
Published: March 2011

AbstractThe amount of plastic components of passenger cars in Japan has increased extremely past 25 years. Many of them are produced by injection molding. There are a number of significant developments in injection molding technology. These developments involve CAE (Computer Aided Engineering) including the prediction of the properties of molded parts, innovative experiments to analyze processing, new machineries (processing) and recycling plastics.