bluuebunny/crossref_metadata_2025_split huggingface dataset:
Gas separation using polymer membranes: an overview
Authors: Ghosal Kanchan , Freeman Benny D. 
Published: April 2003

AbstractThis overview article discusses fundamental principles of gas sorption and transport in rubbery and glassy polymers and material selection guidelines for gas separation membranes. Comparisons between the performance of membrane‐based gas separation systems and more conventional technologies in key commercial applications are provided. Companion articles in this special edition focus on state‐of‐the‐art reviews and descriptions of theoretical and experimental developments important in the technology of gas separations using polymeric membranes.
Molecular modeling studies of polymeric gas separation and barrier materials: structure and transport mechanisms
Authors: Jacobson Solomon H. 
Published: April 2003

AbstractMolecular modeling studies have been completed on cis‐PTBA(poly(tert‐butylacetylene)) and Sixef44 polyimide, two glassy polymers that can be used to form gas separation membranes. The modeling studies show that polymer backbone bond rotations in PTBA are not thermally allowed. This leads to a helical structure for the cis‐PTBA chains which pack as if the helices were rigid rods. Here, polymer free volume is formed by the interstitial space between adjacent helices, and gas transport occurs via continuous diffusion through the resulting channel‐like free volume. On the other hand, Sixef44 exhibits a flexible polymer backbone, which leads to the formation of irregular voids. In this case, gas molecules are free to move within the voids, but transport occurs only by hopping to an adjacent void, or by void diffusion. In either case, gas transport is closely coupled to polymer backbone motion. Thus, these studies suggest two different types of free volume and gas transport mechanisms. The diffusion mechanism in glassy polymer membranes will depend on the nature of the free volume (e.g. the type of chain packing), and the polymer backbone chain flexibility.
Morphology and thermomechanical properties of latex films
Authors: Gauthier Catherine , Perez Jo 
Published: April 2003

AbstractLatex films involve polymers, copolymers and (or) polymer blends, with more or less complex morphologies. First of all, the mechanical behavior of their amorphous polymeric component is considered. A theoretical approach, which relates macroscopic behavior to molecular processes, is used to model its dynamic mechanical properties and also plastic behavior. Then, in the case of heterogeneous films, we propose that information about the morphology of samples can be deduced from a comparison of their measured viscoelastic properties with the corresponding properties calculated for a suitable model. After a brief review of the theoretical approaches for the mechanical behavior of multiphase systems, we show the validity of the procedure in the case of latex films obtained from different copolymerization pathways. Thus, it is possible (a) to get information about the morphology of binary systems, (b) to determine the stability of the morphology, and (c) to characterize a third phase as an interphase between nodules and matrix. High stress–strain behavior is discussed in the case of latex films reinforced with nanoparticles of silica or with cellulose whiskers.
Relationship between structure and rheological properties in the melt of polymers containing spherical inclusions
Authors: Bardollet P. , Bousmina M. , Muller R. 
Published: April 2003

AbstractThe linear viscoelastic behavior of model rubbertoughened polymer melts has been studied. The most significant influence of the dispersed crosslinked rubber phase on the melt rheology of the blends is the existence of a secondary plateau for the storage modulus G′ at low frequencies. This behavior was ascribed to a percolation phenomenon, leading to the formation of a threedimensional network of inclusions, and contributing to the elasticity at low frequencies of the blend. Two different systems were investigated: (a) a polystyrene matrix with crosslinked and structured latex particles and (b) silicon oil matrices with homogeneous crosslinked PMMA particles. An initial shearing history was found to influence the dynamic mechanical properties of the molten blends and in particular to lower the lowfrequency plateau value for G′. During a subsequent annealing, the plateau modulus increases again. These results are in agreement with the assumption of a particle network.
Synthesis and properties of urethane elastomer‐modified epoxy resin having hydroxymethyl group
Authors: Ohtsuka Keiko , Hasegawa Kiichi , Fukuda Akinori 
Published: April 2003

AbstractSynthesis and properties of urethane elastomer‐modified epoxy resins were studied. The urethane elastomer‐modified epoxy resins were synthesized by the reaction of a 4‐cresol type epoxy compound having hydroxymethyl groups (EPCDA) with isocyanate prepolymer. The structure was identified by IR, 1H NMR and GPC. These epoxy resins (EPCDATDI) were mixed with a commercial epoxy resin (DGEBA) in various ratios. The mixed epoxy resins were cured with a mixture of 4,4′‐diaminodiphenylmethane and 3‐phenylenediamine (molar ratio 6:4) as a hardener. The curing behaviour of these epoxy resins was studied by DSC. The higher the concentration of EPCDATDI, the higher the onset temperature and the smaller the rate constant (k) of the exothermic cure reaction were. It was considered that the ratio of hydroxymethyl group to epoxide group was very small and the molecular weight of EPCDATDI was large. Therefore, the accelerating effect of the hydroxymethyl group on the epoxide–amine reaction was cancelled by the retardant effect of increased molecular weight and viscosity, and decreased molecular motion. Toughness was estimated by Izod impact strength and fracture toughness (K1C). On addition of 10 wt% EPCDATDI with low molecular weight (M̄n 6710, estimated by GPC using polystyrene standard samples), Izod impact strength and K1C increased by 70% and 60%, respectively, compared with unmodified epoxy resin. Glass transition temperatures (Tg) for the cured epoxy resins mixed with EPCDATDI measured by dynamic mechanical spectrometry were the same as those of unmodified epoxy resin. The storage modulus (E′) at room temperature decreased with increasing concentration of EPCDATDI. Toughness and dynamic mechnical behaviour of cured epoxy resin systems were studied based on the morphology.
Stereoregularity in poly[methyl(3,3,3‐trifluoropropyl)siloxane]
Authors: Kuo Chung‐Mien , Saam John C. , Taylor Richard B. 
Published: April 2003

AbstractAnionic ring‐opening polymerization of the cis and trans isomers of 1,3,5‐trimethyl‐1,3,5‐tris(3′,3′,3′‐trifluoropropyl)cyclotrisiloxane (cis‐ and trans‐F3) and their mixtures was conducted under conditions that suppressed siloxane bond redistribution in order to preserve stereoregularity formed in the resulting poly[methyl(3,3,3‐trifluoropropyl)siloxane] (PMTFPS). Proton decoupled 19F NMR of the resulting polymers was interpreted by assuming that the original stereoconfiguration of the monomer was preserved and that the monomer inserted with a roughly equal probability of forming meso or racemic configurations relative to the configuration of the reacting chain end. Polymers from cis‐F3 were solid and crystalline at room temperature while the more typical polymers from mixtures of isomers containing greater than 50% trans‐F3 were liquid and amorphous.
Poly(2,2‐dimethyltrimethylene carbonate)‐block‐poly(dimethylsiloxane)‐block‐poly(2,2‐dimethyltrimethylene carbonate). Synthesis and thermal properties
Authors: Müller Achim J. , Keul Helmut , Höcker Hartwing 
Published: April 2003

AbstractLithium salts of hydroxytelechelic poly(dimethylsiloxane) [poly‐(DMS)] were used as initiators for the anionic ring‐opening polymerization of 2,2‐dimethyltrimethylene carbonate (DTC). Triblock copolymers were obtained in high yields. Complexation of the active site in DTC polymerization by the poly(DMS) chain leads to a decrease in polymerization rate. The thermal properties of the copolymers of different compositions were determined. Catalysed thermal degradation of the block copolymers leads to cyclic oligomers Dn and DTC upon ring‐closing depolymerization.
Some light on the concept of unreactivity arising from active center association in anionic polymerizations
Authors: Young R. N. , Fetters L. J. , Huang J. S. , Krishnamoorti R. 
Published: April 2003

AbstractA long held assumption in hydrocarbon based anionic polymerization involving organolithiums is that the aggregated species are unreactive and thus serve only as reservoirs from which the active singlet species momentarily emerge to participate in the initiation or propagation events. This work demonstrates that contrary to the notion of aggregate dormancy such species can participate in monomer addition. The approach involved freeze‐dried vitrified polystyryllithium which was found to be reactive toward butadiene and methanol vapors. The sub‐glass transition state of the polystyryllithium eliminates the establishment of the aggregate: singlet equilibrium as a result of the inability of chains to undergo diffusion. Furthermore, it is shown that the lower bound gradient for the dependence of propagation rate on active center concentration, within experimental error, is about 1/5 for the majority of those diene systems where the active center concentration covers at least two decades. A computer evaluation of the propagation rate: active center data was done with the aim of testing and determining the equilibrium constants of these aggregated systems.
Synthesis and properties of fluorinated polyimides and fluorinated poly(imide amide)s containing pendent cyano groups
Authors: Mercer Frank W. , McKenzie Martin T. , Bruma Maria , Schulz Burkhard 
Published: April 2003

AbstractA series of fluorinated polyimides and fluorinated poly(imide amide)s containing pendent cyano groups were prepared and investigated to determine their dielectric constants as a function of relative humidity and thermal characteristics. The fluorinated polymides and fluorinated poly(imide amide)s containing pendent cyano groups were prepared by reaction of bis(4‐aminophenoxy) benzonitriles with a fluorinated dianhydride and with a fluorinated di(acid chloride) containing preformed imide rings. The properties of the fluorinated polyimides and fluorinated poly(imide amide)s containing pendent cyano groups were compared with those of fluorinated polyimides and fluorinated poly(imide amide)s prepared from 1,3‐bis(4‐aminophenoxy)benzene. The introduction of the pendent cyano groups caused an increase in the dielectric constant and an increase in the glass transition temperature of the polymers compared with the polymers prepared without pendent cyano groups.
Optimum reaction conditions for polypyrrole film deposition with some iron(III) compounds
Authors: Ayad Mohamad M. 
Published: April 2003

AbstractThe optimum reaction conditions for the deposition of smooth conductive polypyrrole (PP) films were monitored using a quartz crystal microbalance technique. This is for oxidative polymerization of pyrrole with some iron(III) compounds. The FeCl3 · 6H2O/pyrrole system in aqueous solution at 20 ± 0.5°C was examined in some detail. The effect of the initial molar ratio of the reactants on the yield and the growth rate of the PP film deposition was studied. The optimum molar ratio was found to be approximately 2.4 ± 0.1. A comparison between the growth rate of the PP films was made when different iron(III) compounds were used. The rate is shown to be affected by the nature of the anions in these compunds.
Crystal structure of the poly(ethylene oxide)–p‐nitrophenol molecular complex
Authors: Damman P. , Point J. J. 
Published: April 2003

AbstractA crystalline complex of poly(ethylene oxide) (PEO) and p‐nitrophenol (PNP) was studied by differential scanning calorimetry, X‐ray diffraction, and FTIR spectroscopy, The phase diagram of this system is characterized by a peritectic reaction, and reveals the formation of a new crystal form different from those of PEO, and PNP. The triclinic unit cell of the complex was determined from the X‐ray diffraction patterns of differently oriented samples obtained by mechanical deformations or spherulitic crystallizations. Finally, the molecular packing and the conformation adopted by the PEO chains were determined by FTIR spectroscopy. Polarization measurements have shown that the aromatic rings are very nearly normal to the c parameter (chain axis) and that the 1–4 axes of PNP molecules are parallel to the a* reciprocal parameter (spherulitic growth direction). Finally, a new (t2 gt2 gt3) conformation is proposed for the PEO chains on the basis of a normal mode analysis and the calculation of the intramolecular energy.
Effect of ammonium derivatives of oligoamidephosphates on the vulcanization characteristics and mechanical properties of some rubber compounds. 1. Isoprene rubber compounds
Authors: Vladkova Todorka G. , Arnaudova Rumyana V. 
Published: April 2003

AbstractIR compounds containing ammonium derivatives of oligoamidephosphates were studied with respect to vulcanization and mechanical characteristics. The ammonium derivatives were obtained as neutral analogues of the corresponding oligoamidephophates. The results indicate an improved efficiency of the neutral products and the possibility of a partial replacement of traditional sulphenamide accelerators with the studied ammonium derivatives, leading to a strong improvement of the fatigue resistance (by more than one order).The addition of such products without reducing the level of the basic accelerator led to additional acceleration—the cure rate increased and the cure time decreased up to three times. Ageing resistance showed a tendency to improve.
Comparison of interdiffusion at polystyrene–poly(vinyl methyl ether) and polystyrene–poly(isobutyl vinyl ether) interfaces
Authors: Jabbari Esmaiel , Peppas Nikolaos A. 
Published: April 2003

AbstractThe effect of polymer–polymer compatibility on interdiffusion at polymer interfaces with dissimilar mobilities was investigated by attenuated total internal reflectance infrared spectroscopy. The polymer pair consisting of polystyrene and poly(vinyl methyl ether) was used to study interdiffusion at the interface of compatible polymers. The polymer pair consisting of polystyrene and poly(isobutyl vinyl ether) was used to study interdiffusion at the interface of incompatible polymers. Results indicate that the extent of interdiffusion is controlled by the polymer–polymer compatibility parameter, irrespectively of the differences in the mobility of the polymers.
Polymer networks based on α,ω‐methacrylate‐terminated poly(1,3‐dioxolane)
Authors: Walraedt Saskia R. , Goethals Eric J. 
Published: April 2003

Abstractα,ω‐Methacrylate‐terminated poly(1,3‐dioxolane)s (polyDXL) were synthesized by cationic ring‐opening polymerization of DXL in the presence of methylene‐bis(oxyethylmethacrylate) as transfer agent. If the initiator concentration is small compared with the transfer agent concentration, the molecular weights of the polymers are governed by the ratio of the reacted monomer to the reacted transfer agent. The α,ω‐methacrylate‐terminated polyDXLs obtained undergo free radical polymerization with formation of polyacetal networks. The properties of the networks as function of the molecular weight of the corresponding prepolymers are reported.
Dynamic mechanical characterization of gel phase in high impact polystyrene
Authors: Keskkula Henno , Turley S. G. 
Published: April 2003

AbstractThe mechanical properties of the reinforcing phase of rubber modified polymers are important in determining the performance of the composite material. Of particular interest are the modulus values of the rubber particle phase. Stress concentrations in the rigid phase are determined by the shear modulus of the rubber particles; therefore, the knowledge of these values would be helpful in studying the crazing phenomenon in rubber modified polymers.For this reason the gel phase of a rubber modified polystyrene was separated by high speed centrifugation and shear modulus determinations made by means of a torsion pendulum over a wide temperature range.
Caracterisation des polyamides par chromatographie sur gel (GPC) en milieu hexamethylphosphorotriamide
Authors: Panaris R. , Pallas G. 
Published: April 2003

AbstractL'insolubilité des polyamides dans les solvants classiques a toujours été un frein à la détermination de leurs caractéristiques physico‐chimiques en solution.Les solvants les plus communément utilisés pour ce type d'étude sont l'acide formique, le phénol, le trifluoroéthanol, le m‐crésol.Si L'étude des polyamides 6 est possible dans ces solvants (1) (2) avec cependant de nombreuses difficultés (3), les polyamides 11 et 12 se prêtent mal à l'étude par chromatographie sur gel d'une part à cause de leur insolubilité dans le trifluoroéthanol, d'autre part à cause de leur incrément d'indice nul ou faible dans le méta‐crésol.Dans ce travail, nou montrons que l'hexaméthylphosphorotriamide est un solvant parfaitement adapté et facile à utiliser pour la chromatographie de partage en phase liquide (GPC). Comme ce produit est aussi un excellent solvant du polystyréne, il est possible d'étalonner l'appareil à partir d'étalons de polystyrène. On montre enfin que ce solvant est utilisable pour de nombreux autres types de polymére.
Bioengineering functional copolymers. III. Synthesis of biocompatible poly[(N‐isopropylacrylamide‐co‐maleic anhydride)‐g‐poly(ethylene oxide)]/poly(ethylene imine) macrocomplexes and their thermostabilization effect on the activity of the enzyme penicillin G acylase
Authors: Köseli Volkan , Rzaev Zakir M. O. , Pişkin Erhan 
Published: April 2003

AbstractStimuli‐responsive poly[(N‐isopropylacrylamide‐co‐maleic anhydride)‐g‐poly(ethylene oxide)]/poly(ethylene imine) macrobranched macrocomplexes were synthesized by (1) the radical copolymerization of N‐isopropylacrylamide and maleic anhydride with α,α′‐azobisisobutyronitrile as an initiator in 1,4‐dioxane at 65 °C under a nitrogen atmosphere, (2) the polyesterification (grafting) of prepared poly(N‐isopropylacrylamide‐co‐maleic anhydride) containing less than 20 mol % anhydride units with α‐hydroxy‐ω‐methoxy‐poly(ethylene oxide)s having different number‐average molecular weights (Mn = 4000, 10,000, or 20,000), and (3) the incorporation of macrobranched copolymers with poly(ethylene imine) (Mn = 60,000). The composition and structure of the synthesized copolymer systems were determined by Fourier transform infrared, 1H and 13C NMR spectroscopy, and chemical and elemental analyses. The important properties of the copolymer systems (e.g., the viscosity, thermal and pH sensitivities, and lower critical solution temperature behavior) changed with increases in the molecular weight, composition, and length of the macrobranched hydrophobic domains. These copolymers with reactive anhydride and carboxylic groups were used for the stabilization of penicillin G acylase (PGA). The conjugation of the enzyme with the copolymers significantly increased the thermal stability of PGA (three times at 45 °C and two times at 65 °C). © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1580–1593, 2003
Synthesis and radical polymerization of hydrophilic methacrylates with oxyethylene units in the pendant chain
Authors: García F. , García J. M. , Rubio F. , de la Peña J. L. , Guzmán J. , Riande E. 
Published: April 2003

AbstractThe syntheses of methacrylic monomers of the general structure
magnified image
where n is 3, 4, 5, or 6, were performed by the reaction of the corresponding alcohol ethers with methacryloyl chloride. The alcohol ethers were previously prepared by different synthetic procedures involving the monoetherification of the starting glycols. The polymerizations kinetics of the monomers were examined at several temperatures in the bulk and in dioxane solutions. NMR spectroscopy and electron paramagnetic resonance techniques were used to study the kinetics of polymerization. The polymerization rate parameter, expressed as (2f)1/2kp/〈kt〉1/2, and the values of the propagation rate coefficient kp and the termination rate coefficient 〈kt〉/f, where f is the efficiency factor of the initiator, were determined. The reactivity of the monomers depended on the size of the ester residue in such a way that the longer the lateral chain was, the higher the polymerization rate was and the lower the termination rate coefficient was. On the contrary, the dependence of kp on the chemical structure was very small. In the solution polymerizations of all these monomers (monomer concentration = 1 mol L−1), the radical concentrations remained almost constant until very high conversions, whereas in the bulk, a different behavior was observed that depended on the number of oxyethylene units in the side chain of the monomer. In this sense, for n = 4, 5, or 6, the radical concentration remained almost invariable with the reaction time, whereas for n = 3, a moderate increase occurred at low conversions, contrasting with the important increase observed at similar conversions for n = 1. This showed that the gel effect in these methacrylic monomers was greatly dependent on the number of bonds of the lateral chain. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1567–1579, 2003
Preparation and characterization of crosslinked poly(N,N‐diethylacrylamide‐co‐2‐hydroxyethyl methacrylate) resins and their application as support in solid‐phase peptide synthesis
Authors: Wang Zheng , Song Zhengji , Zhu X. X. 
Published: April 2003

AbstractNovel hydrophilic and thermosensitive poly(N,N‐diethylacrylamide‐co‐2‐hydroxyethyl methacrylate) resins were prepared by inverse suspension polymerization with N,N′‐methylenebis(acrylamide) as a crosslinker. The effects of chemical composition and degree of crosslinking on the polymerization were investigated. The polymer resins were characterized by elemental analysis, infrared spectroscopy, differential scanning calorimetry, and scanning electron microscopy. The thermosensitivity of the crosslinked resins was demonstrated by their lower critical swelling temperatures. The swelling and deswelling volume of the beads in water varied depending on the molar fraction of the N,N‐diethylacrylamide. These beads swelled extensively in a variety of common solvents. They had high loadings of functional hydroxyl groups and were used as supports in the solid‐phase synthesis of an oligopeptide. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1681–1690, 2003