bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polymerizable phospholipids: a novel class of biomaterials
Authors: Singh Alok , Schnur Joel M. 
Published: April 2003

AbstractPolymerizable phospholipids are organic monomers that are able to self‐assemble into membranes. This is quite similar to the self assembly of naturally occurring lipid membranes found in biological systems. The polymerizable lipids can then be polymerized to stabilize these membranes. These stabilized structures have a number of different morphologies which offer a variety of technically attractive features. This article reviews the chemical and physical properties of these materials in terms of their technological applications.
Effect of the thermal history on the phase transition and the liquid crystalline structure of thermotropic polyesters
Authors: Lee Young Jun , Kim Sung Chul 
Published: April 2003

AbstractA series of triad type thermotropic polyesters based on phenylsulfonyl hydroquinone and α,ω‐bis(4‐carboxyphenoxy)alkane was prepared, and the effect of the thermal history on the phase transition and the liquid crystalline structure of the polyesters was studied. The phase transition was significantly affected by the thermal history. When annealed at various temperatures, multiple endotherms were observed for all polyesters in DSC thermograms. A phase stability concept was employed to explain the complicated phase transitions. The time evolution of the liquid crystalline structure was investigated by optical microscopy and transmitted light intensity measurement under crossed polars during annealing. The steady decrease in the density of disclinations with accompanying increase of transmitted light intensity was observed. Depending on the surface conditions of the liquid crystal polymer film, two markedly different domain growth patterns and different textures were found on isothermal annealing; the continuous wormlike texture and the discontinuous droplet texture. The structural relaxation of the deformed texture during annealing was also studied. When shear was applied, the characteristic banded texture was formed in all polyesters.
Oxygen‐binding property of hemoglobin films
Authors: Chung Jooeun , Takeoka Shinji , Nishide Hiroyuki , Tsuchida Eishun 
Published: April 2003

AbstractOxygenated and deoxygenated hemoglobin films were obtained by drying corresponding hemoglobin solutions with maltose (≧0.3 M). The resulting hemoglobin films were homogeneous and smooth, and the methemoglobin formation in the oxyhemoglobin film was well suppressed. The dry, rigid networks of maltose molecules work to preserve the conformation of hemoglobin against the removal of water. The coordination of oxygen to the deoxygenated hemoglobin film was slow and saturated up to 50%, while nearly 100% saturation was achieved if the film contained a residual moisture of 8.7%.
Conducting composites from EPDM–EVA blends
Authors: Ghosh M. K. , Das C. K. 
Published: April 2003

AbstractThe effect of ethylidene norbornene (ENB) content of ethylene propylene aiene rubber (EPDM) and vinyl acetate (VA) content of ethylene vinyl acetate copolymer (EVA), as well as the blending sequence, on the conductivity of composites based on EPDM–EVA–carbon black have been studied. Black master batches show a lower extent of cure than the preblended system followed by black addition. EPDM having a high ENB content shows higher conductivity under ambient conditions. Preblended systems give rise to higher conductivity in the case of low‐ENB content EPDM. But for high‐ENB content EPDM, the blending of black master batches imparts high conductivity. Two types of conduction are observed in this case and the transition temperature depends on the VA content of EVA. It appears that there exists a correlation between activation energy of curing and that of conduction.
Mechanical and thermal properties of dragline silk from the spider Nephila clavipes
Authors: Cunniff Philip M. , Fossey Stephen A. , Auerbach Margaret A. , Song John W. , Kaplan David L. , Adams W. Wade , Eby Ronald K. , Mahoney David , Vezie Deborah L. 
Published: April 2003

AbstractDragline silk from the spider, Nephila clavipes, was characterized by thermal analysis (TGA, DSC, DMA), computational modeling, scanning electron microscopy and by quasi‐static as well as high rates of strain. Thermal stability to about 230°C was observed by TGA, two transitions by DMA, −75°C, representative of localized motion in the amorphous domain, and a main chain motion associated with partial melt at 210°C. Tensile tests indicated average initial modulus, ultimate tensile strength and ultimate tensile strain of 22 GPa, 1.1 GPa and 9%, respectively. The corresponding properties of the best fibers tested were 60 GPa, 2.9 GPa and 11%, respectively. High strain rates (>50,000%/sec) indicated similar mechanical properties to the average values indicated above. Microscopy showed compressive and tensile strains to failure of 34%. Computational modeling yielded a crystal modulus of 200 GPa.
Thermotropic behavior of aromatic copolyesters based on 3,4′‐substituted diphenyl ether
Authors: Carpaneto Luca , Costa Giovanna , Marsano Enrico , Morinelli Sergio , Piombo Vadim , Valenti Barbara 
Published: April 2003

AbstractRecently, flexible rod‐like monomers based on conformational isomerism have been used to synthesize fully aromatic thermotropic polymers of reduced processing temperature and good thermal stability. 3,4′‐Dihydroxy and 3,4′‐dicarboxydiphenyl ethers HE and DE, obtained by modified Ullmann condensations between proper hydroxy and bromo derivatives, are investigated as basic components for homo‐ and copolyesters with the above‐mentioned characteristics. Homopolymers from HE and terephthaloyl chloride or DE chloride and 2‐methyl (or phenyl) hydroquinone, synthesized by low temperature solution polycondensation, melt to an isotropic fluid; the chain packing is frustrated in the latter by asymmetrical substitution on the aromatic rings, which causes a sequence randomization as well as an increased chain separation. The incorporation of linear rigid units, by partial substitution of the flexible monomers with 1,4 aromatic moieties, leads to thermotropicity, but the critical content of 1,4 units varies with the steric hindrance of the diphenol. Variation of chain rigidity, arising from the chemical structure, composition and sequence distribution, can account for the thermal behavior of the samples and, in particular, for their different abilities to give liquid crystalline behavior.
Improvement of the properties of polyarylate reinforced with liquid crystalline polymers
Authors: Zaldua Ane , Muñoz M. Eugenia , Peña Juan J. , Santamaria Anton 
Published: April 2003

AbstractBlends of polyarylate of bisphenol A, PAr, with two commercial main chain liquid crystalline polymers, Vectra A950 and Vectra B950, are studied. From dynamic viscoelastic measurements it is deduced that both systems (PAr/Vectra A950 and PAr/Vectra B950) are immiscible and scanning electron microscopy (SEM) micrographs show the presence of spherical domains of the liquid crystalline polymer when PAr constitutes the matrix. Extrusion capillary measurements reveal that, under conditions of temperature and shear rate similar to those of processing, the viscosity is reduced to approximately 10% of its value when the content of liquid crystalline polymer is only 20%. This great improvement of the rheological properties is observed in both PAr/Vectra A950 and PAr/Vectra B950 blends. The effect of draw ratio on Young's modulus for different compositions is also analyzed, pointing out the reinforcing action of both liquid crystalline polymers on polyarylate: for instance, 20% of Vectra B950 in the blend gives rise to a 700% increase of the modulus of fibres prepared at a draw ratio of 50. SEM of the extrudates reveals that the spherical domains are elongated at the entrance of the capillary giving rise to a microfibrillar morphology which is related to the excellent rheological and mechanical properties of the blends.
Utility of a liquid crystalline diacrylate for bistable switching cholesteric gel displays
Authors: Behrens Ulrike , Kitzerow Heinz‐Siegfried 
Published: April 2003

AbstractWe investigated cholesteric liquid crystals containing an anisotropic polymer network created by in situ photo‐polymerization of a mesogenic diacrylate. In contrast to previous studies, we used a liquid crystalline diacrylate to achieve bistable switching between the reflecting Grandjean texture and the diffuse scattering focal conic texture. The switching behavior depends considerably on the orientation of the liquid crystal during the polymerization. For polymerization in the Grandjean texture, the response times for switching to the reflecting state were lowered compared to the pure liquid crystal. The chromaticity coordinates indicate that this new type of display is very promising for additive color mixing.
Carbon–epoxy composites based on fibers coated with nylon 6,6: hygrothermal ageing versus interlaminar shear strength
Authors: Duvis T. , Papaspyrides C. D. 
Published: April 2003

AbstractCarbon fibers were coated in situ with a thin film of polyhexamethylene adipamide by an interfacial polycondensation technique. The modified fibers were used for the preparation of epoxy‐based unidirectional composites. Specimens of these materials were immersed in water until equilibrium conditions were attained. The weight gain at equilibrium was determined as a function of the immersion temperature, the fiber volume fraction and the polyamide content deposited on the fibers. Water penetration in specimens made with uncoated carbon fibers increases when the volume fraction decreases. Introduction of the polyamide interlayer initially increases the water absorption, but reduces it at higher immersion temperatures and/or higher polyamide contents. The treated specimens were subjected to the short beam test to determine the interlaminar shear strength (ILSS). The data show that the ILSS decreases with water penetration but increases when the immersion temperature increases from 40 to 70°C. The overall performance encountered is discussed in terms of the possible roles of the polyamide interphase while taking into account mechanisms concerned with matrix plasticization, interphase degradation and residual stress relaxation.
Cyclic polymers: past, present and future
Authors: Semlyen J. A. , Wood B. R. , Hodge P. 
Published: April 2003

AbstractMethods for characterising cyclic polymers are illustrated by reference first to dilute solution methods for cyclic poly(dimethylsiloxane) (PDMS) and then to the entrapment of cyclic polymers in networks. Preparative routes to cyclic polymers are then reviewed, including ring‐chain equilibration reactions, coupling and condensation reactions and new methods using polymer‐supported reagents. Some of the properties of cyclic PDMS are discussed, including differences between ring and chain polymer properties such as their melt viscosities and glass transition temperatures. Methods for preparing the first polymeric catenanes are described, using polymer‐supported reagents. Future directions for cyclic polymer chemistry are indicated, including topological polymer chemistry.
Stabilization of vinylidene chloride barrier resins
Authors: Howell B. A. , Warner B. S. , Rajaram C. V. , Ahmed S. I. , Ahmed Z. 
Published: April 2003

AbstractVinylidene chloride copolymers have a number of superior properties, most notably a high barrier to the transport of oxygen and other small molecules. As a consequence, these materials have assumed a position of prominence in the packaging industry. At processing temperatures these copolymers tend to undergo degradative dehydrochlorination. Unsaturation generated via interaction of the polymer with a variety of agents commonly encountered during polymerization or processing introduces an allylic dichloromethylene unit which may function as a major defect (labile) site for the initiation of degradation. Three approaches to the potential stabilization of these materials have been examined. The first involved the addition of agents, e.g. metal formates, capable of converting labile dichlormethylene units into non‐reactive groups which would interrupt propagation of the degradative dehydrochlorination. The second involved the incorporation into the polymer of a commoner capable of scavenging free chlorine atoms. The third involved the preparation of copolymers which contains units capable of reaction with (consumption of) a mole of hydrogen chloride to expose a good free radical stabilizer to scavenge chlorine atoms.
Development of radiation‐grafted FEP‐g‐polystyrene membranes: Some property–structure correlations
Authors: Gupta Bhuvanesh , Büchi Felix N. , Scherer Günther G. , Chapiro Adolphe 
Published: April 2003

AbstractProperty–structure correlation in proton exchange membranes, prepared by simultaneous radiation grafting of styrene into FEP films and their subsequent sulfonation, was evaluated. The distribution of ionic sites across the membrane matrix was determined by microprobe measurements. The properties of these membranes, such as ion exchange capacity, swelling and ionic resistivity as a function of the degree of grafting, were studied. The thermal stability of membranes was studied using thermogravimetric analysis and ion exchange capacity measurements. Membranes undergo considerable structural changes in terms of the increase in the ionic content, enhanced hydrophilicity and decrease in crystallinity with the increasing degree of grafting. A correlation between some physical properties and stuctural changes occurring during the membrane preparation was established.
Synthesis of poly(sulfonium cation) as an alkylating reagent
Authors: Shouji E. , Nishimura S. , Yamamoto K. , Tsuchida E. 
Published: April 2003

AbstractMethyl 4‐phenylthiophenyl sulfoxide is polymerized to poly(methyl‐4‐phenylthiophenylsulfonium) in poly(phosphoric acid) with a yield higher than 90%. The demethylation of poly(sufonium cation) is examined to control the composition ratio of the thiophenylene unit in the polycation. The polycation is soluble in common solvents due to the alternative structure of phenylene sufide and phenylenesulfonium cation and is easily converted to poly(phenylene sulfide) through the demethylation with a nucleophile. The poly(sulfonium cation) can be applicable as an alkylating agent for phenol, aniline and benzoic acid to the corresponding to anisole, N‐methyl aniline, N,N‐dimethyl aniline and benzoic methyl ester, respectively, with high conversion through the demethylation. These products can be isolated without a complicated purification because poly(phenylene sulfide) is precipitated in the mixture as the side product due to the poor solvent solubility.
Development of natural product (1 → 3)‐β‐D‐glucan polymers as immune‐stimulating pharmaceuticals
Authors: Williams David L. , Browder I. William 
Published: April 2003

AbstractGlucan phosphate is a water‐soluble, yeast‐derived, (1 → 3)‐β‐D‐glucopyranose polymer that has been demonstrated to be a potent immune stimulant. Glucan phosphate administration is associated with stimulation of immunity and a concomitant increase in resistance to a variety of experimentally induced disease states. Preclinical safety evaluation indicates that glucan phosphate does not induce mortality or significant toxicity over a wide dose range. Phase I clinical data indicate that glucan phosphate will ameliorate immunosuppression, stimulate immunity, decrease susceptibility to infection and alter ultimate outcome in trauma patients following laparotomy or thoracotomy. This work reviews the development, characterization, preclinal and clinical evaluation of glucan phosphate.
The α‐halogeno ether function: formation and use in the design of tailor‐made polymers
Authors: Cramail Henri , Schappacher Michel , Deffieux Alain 
Published: April 2003

Abstractα‐Halogeno ether species, in appropriate conditions, can induce the “living” cationic polymerization of vinyl ethers. They can also be used as initiators for the “living” polymerization of styrene derivatives. Therefore, their use as intermediates in the preparation of tailor‐made polymers and copolymers offers interesting opportunities in macromolecular synthesis. The main parameters which determine and control their reactivity are reviewed and discussed. The possibility to generate quantitatively these derivatives by various routes and from different organic functions such as aldehyde, ketone, acetal and hydroxyl is examined. Some of these routes have been used to generate the α‐halogeno ether function directly at the end of acetal and hydroxy‐terminated polymers. The latter have then been used as macroinitiators to prepare new block copolymers. The synthesis of poly(isobutyl vinyl ether‐β‐ethyl vinyl ether), poly(styrene‐β‐chloroethyl vinyl ether) and poly(chloroethyl vinyl ether‐β‐butadiene‐β‐chloroethyl vinyl ether) by this technique is described.
Methotrexate polymer implant for the treatment of head and neck cancer
Authors: Domb Abraham J. , Wartenfeld Rita 
Published: April 2003

AbstractA biodegradable polymeric device releasing methotrexate (MTX) for the treatment of cancer of the head and neck was evaluated in vitro and in vivo. The polymer used for the preparation of the device was a copolyanhydride based on dimer erucic acid and sebacic acid loaded with 2–20% MTX. The drug was released constantly for about two weeks from small discs (1 × 3 mm) with complete degradation of the polymer when placed in phosphate buffer pH 7.4 at 37°C. The release and degradation rate was similar for all drug loading. MTX‐loaded discs implanted subcutaneously in mice released the drug for about ten days with about 50% elimination of the device from the implantation site. The drug concentration was the highest in the tissue in contact with the device and decreased at distance from the device following a first order kinetics. The LD50 of MTX in polymer when implanted in mice was between 20 and 40 mg per kg. (1994)
Miscible blends through hydrogen bonding: effects on polymer properties
Authors: Pearce Eli M. , Kwei T. K. , Lu Shaoxiang 
Published: April 2003

AbstractMiscible blends through hydrogen bonding have been intensively studied. The effects of a variety of miscible hydrogen bonded polymer blends on properties such as thermal and thermal oxidative stability, moisture sensitivity, modulus and glass transition temperature are discussed. In addition, the preparation of semi‐interpenetrating polymer networks (IPNs) and studies of the effect of crosslinking on the miscibility in hydrogen bonded polymer blends are reviewed.
The preparation, compatibility and structure of PEEK–PES blends
Authors: Ni Zhuo 
Published: April 2003

AbstractBlends of polyetheretherketone and polyethersulfone (PEEK–PES blends) were prepared either by mechanically mixing fine PEEK and PES powders or by mixing PEEK and PES solutions in H2SO4 (98%). Partially compatible blends were obtained in the latter method. The sulfurization of PEEK or PES in concentrated sulphuric acid did not occur provided that the experiment was performed within 30 min. The Tg of the PEEK component increased and that of PES component decreased with the increase of PES weight fraction; the melting exothermic peak of the PEEK component did not appear in the DSC curves of the quenched blends, suggesting that PES can effectively reduce the crystallization of PEEK component. The major absorbances of the bands were characterized by IR spectroscopy; the frequency difference between PEEK or PES and their blends were observed. A linear correlation of absorbance ratios with PEEK weight fraction was found.
Morphology and physical properties of a liquid–crystalline main‐chain polymer with flexible side chains
Authors: Damman S. B. , Buijs J. A. H. M. , Mercx F. P. M. 
Published: April 2003

AbstractA molecular laminate model is used to explain the properties of unoriented and oriented films of poly(p‐phenylene‐2,5‐didodecyloxyterephthalate) cast from solution. In oriented films the two different crystal modifications, A and B, give rise to room temperature tensile moduli of 15 and 30 GPa respectively. The packing (in clusters) of the side chains in modification A, leading to a glass–like transition in the side‐chain regions around −40°C, is largely responsible for this difference. Oriented films of modification A and B have coefficients of thermal expansion of +0.3×10−5 and −1× 10−5 K−1 respectively. It is concluded that the properties of this class of polymers can be adjusted in a systematic way.
Recent advances in the formation of ultrathin polymeric membranes for gas separations
Authors: Pinnau Ingo 
Published: April 2003

AbstractDuring the past 20 years membrane systems have been applied to a limited number of commercial gas separations. To further advance membrane‐based gas separations, current research efforts focus on optimization of (i) membrane materials, (ii) membrane structures and (iii) membrane system design. In this overview, recent developments in the formation of high‐performance gas separation membranes are discussed. The gas separation properties of state‐of‐the‐art integrally skinned asymmetric membranes and thin‐film composite membranes are summarized. Future directions for the preparation of advanced gas separation membranes are highlighted.
The melt hollow fiber spinning process: steady‐state behavior, sensitivity and stability
Authors: Lipscomb G. Glenn 
Published: April 2003

AbstractThe rheology of the melt hollow fiber spinning process is examined in the thin filament limit. The resulting thin filament equations are also applicable to single‐phase and two‐phase extensional flows. Using a novel numerical solution procedure, the sensitivity of the fiber spinning equations to material property and process variations is investigated. Fiber geometry is directly controlled by the mass flowrates of the core and clad fluids while the spinline tension is most strongly influenced by clad viscosity. A maximum can occur in the clad stress profile if a core liquid is used and the ratio of core to clad viscosity increases greatly with temperature. Isothermal spinning of high viscosity clad liquids with either a core gas or liquid is unstable for draw ratios greater than 20.2 as found for solid fibers.
Thermodynamic functions of thermotropic polyethers based on the semiflexible mesogen 1‐(4‐hydroxyphenyl)‐2‐(2‐methyl‐4‐hydroxyphenyl)ethane
Authors: Jin Yimin , Cheng Jinlong , Wunderlich Bernhard , Cheng Stephen Z. D. , Yandrasits Michael A. 
Published: April 2003

AbstractHeat capacities of a series of thermotropic polyethers consisting of a semiflexible mesogen [1‐(4‐hydroxyphenyl) ‐ 2 ‐ (2 ‐ methyl ‐ 4 ‐ hydroxyphenyl)ethane], with n methylene flexible spacers (n = 4–12) (MBPE‐n) have been measured by DSC and fitted at low temperature to an approximate frequency spectrum, as well as at high temperature to a general equation for the liquid MBPE‐n. The latter equation is:
Cp = n(17.33 + 0.04551T) + (280.9 + 0.3839T)
where n is the number of methylenes in the polyether spacer. The calculated vibration‐only heat capacities start to show deviations from the measured heat capacities below the melting temperature, reflecting contributions from conformational disorder and motion in methylene spacers. It is suggested that part of this increase in heat capacity can be looked upon as a glass transition of the partially conformationally disordered crystals. Solid state 13C–NMR studies showed similarly that over the range of temperature some of the CC bonds in the spacer are in a rotational state similar to that in the melt. The equilibrium heats of fusion (ΔH) and the changes of heat capacity (ΔCp) for the amorphous polymer at the glass transition temperature, Tg, were determined by WAXD and DSC. Based on the discrepancy of ΔCp it is concluded that these phenylene containing polyethers have a certain amount of rigid amorphous polymer. Thermodynamic functions H, S and G for all of the polyethers have been established.