bluuebunny/crossref_metadata_2025 huggingface dataset:
Polystyrene crosslinked with oligomeric and polymeric poly(dimethyl siloxane) derivatives. Thermal and dynamic mechanical studies
Authors: Tenhu Heikki , Heino Eeva‐Leena
Published: April 2003

Styrene has been copolymerized with various bifunctional poly(dimethyl siloxane) cross‐linkers having molar masses in the range 200–35,000. Calorimetric and rheological measurements show that the crosslinkers change Tg, Tll, and Texo, as well as melt viscosity and elasticity of polystyrene. These changes are strongly dependent on the molar mass of the crosslinker. Increasing the length of the siloxane crosslinker lowers Tg and melt viscosity, if the molar mass of the crosslinker is in a range 200–2000. Copolymerizing styrene with a bifunctional poly(dimethyl siloxane) having molar mass near 35,000 leads to a phase‐separated polymer where polystyrene phase largely retains its original properties.
Crystallization of linear polyethylene from melt in isothermal compression
Authors: Kowalewski T. , Galeski A.
Published: April 2003

Crystallization and primary nucleation of linear polyethylene has been studied by means of a custom‐made miniature pressure apparatus. It has been shown that during isothermal compression of linear polyethylene melt at a constant rate crystallization occurs. In the range of fastest conversion rates the crystallization assumes isobaric character. The level of pressure at which the crystallization occurs increases with the increase of the crystal‐lization temperature and/or with the increase of the compression rate. The crystallization has a spherulitic character up to the highest pressure achieved in the apparatus (approx. 600 MPa). Surprisingly, there are no dependencies of average spherulite size, degree of crystallinity, and lamellae thickness on the pressure and the temperature of crystallization during melt compression, but there is a strong relation to the compression rate. Below 250 MPa and above 300 MPa the crystallization proceeds under pressure, ensuring a constant undercooling. The undercooling for the pressure above 300 MPa is approximately 10°C lower than that for the pressure below 250 MPa. For the pressure 250–300 MPa a change in a primary nucleation and spherulite crystallization has been observed that is connected with the transformation from orthorhombic to pseudohexagonal symmetry of crystals. No noticeable effect of molecular weight of linear polyethylene on crystallization during iso‐thermal melt compression has been observed.
Solid state NMR investigation of cationic polymerized epoxy resins
Authors: Egger N. , Schmidt‐Rohr K. , Blümich B. , Domke W.‐D. , Stapp B.
Published: April 2003

Cationic UV‐polymerized resins, based on cycloaliphatic epoxides with aryl sulfonium salts as photoinitiators and polypropylene glycols of variable length as flexibilizers, have been investigated with respect to the network‐forming reactions and the morphology of the resulting polymers. The combination of UV‐curing and thermal postcure makes the chemical process complex and dependent on many variables, such as photoinitiator, exposure time, reaction temperature, and polyol components. Structure and curing of the epoxide were investigated by 13C CPMAS NMR. Morphology and domain sizes were studied by spin diffusion experiments using the novel “dipolar filter” technique for selective magnetization of mobile components.
Ultraviolet‐radiation induced graft‐copolymerization of hydroxyethyl methacrylate onto cotton cellulose
Authors: Shukla S. R. , Athalye A. R.
Published: April 2003

Two‐hydroxyethyl methacrylate was grafted onto cotton cellulose using photoinitiation technique in the presence of the photoinitiator benzoin ethyl ether. Various parameters of the graft‐copolymerization reaction, namely time, temperature, initiator, and monomer concentrations, were optimized using the grafting bath containing 10% methanol/acetone to dissolve the photoinitiator. The cotton sample, preswollen in sodium hydroxide, was subjected to grafting under optimized conditions. The preswollen samples showed higher graft add‐on values at the equivalent monomer concentration. The moisture regain initially decreased at lower graft add‐on levels and increased marginally with higher graft add‐on. This behavior of the grafted substrate with respect to moisture regain has been explained.
Processes of wood delignification and cellulose mercerization under conditions of shear deformations
Authors: Enikolopian N. S. , Balashova E. A. , Sakhonenko L. S. , Rogovina S. Z.
Published: April 2003

The development of high‐yielding and environmentally safe procedures of processing wood and cellulose constitutes a topical problem at present. To facilitate delignification of wood and mercerization of cellulose, a method was proposed, its principle of action based on the use of shear deformations combined with pressure. It is shown that under the conditions of plastic flow the fibrous high‐yield semifinished product produced from birch wood features, due to its specific structure, shows better physicomechanical properties. It is established that under the conditions of high pressure and shear deformations, when cellulose interacts with hard alkali, alkaline cellulose is produced, which is proved by X‐ray analysis data. The depth of wood delignification and cellulose mercerization processes under the conditions of plastic flow does not depend on temperature, i.e., these processes are inactive.
Radiation‐absorbing hydrogel–melanin blends for ocular devices
Authors: Chirila Traian V. , Cooper Richard L. , Constable Ian J. , Horne Robert
Published: April 2003

Hydrophilic polymers and copolymers of 2‐hydroxyethyl methacrylate, with low or high crosslinking density, were synthesized and then treated in aqueous medium with epinephrine (adrenaline) at neutral or acid pH, at room temperature, and in the presence of oxygen and light. During this treatment, a melanin is formed and uniformly dispersed in polymers. The resulting slightly colored hydrogels display radiation‐absorbing properties in the ultraviolet and visible regions of the natural spectrum. This enhances significantly their value as materials for ocular devices (contact lenses, intraocular lenses) that should protect the retina of the patients without their natural lens from potential damage induced by ultraviolet and visible (violet and blue) radiation. The incorporation of common ultraviolet absorbers led to transmittances similar to that of the natural human lens, i.e., 30% or less at 450 nm, 40% or less at 500 nm, and no more than 50% at 700 nm. The two‐phase morphology of the melanized hydrogels, as investigated by TEM, revealed a very fine structure comprising melanin domains of 1 to 12 nm in size. Although no proof for a network interpenetration could be provided, it is believed that the novel blends are true sequential interpenetrating polymer networks.
Heat transfer from moving fibers in melt spinning process
Authors: Chung B. T. F. , Iyer V.
Published: April 2003

The purpose of this study is to develop a steady‐state thermal model for melt spinning of polyester fiber by incorporating the radial heat conduction inside the fiber and the combined effect of radiation and convection at the boundary. The governing equations are obtained from the energy, mass, and momentum balances coupling with the rheological properties of the fibers. The effects of drag, surface tension, gravity, and inertia force are also taken into consideration in the analysis. The velocity profile, temperature profile, and the variation of cross‐sectional area of the filament along the axial direction are solved by employing a finite‐difference scheme.
Modification of polyethylene by unsaturated compounds
Authors: Vijayalakshmi N. S. , Murthy R. A. N.
Published: April 2003

Polyethylene was reacted with maleic anhydride and N‐phenylmaleimide in solution. The effect of modification on its physico–chemical properties, such as mechanical, oxygen gas transmission, water vapor transmission, and grease resistance properties, was studied.
Controlled release of riboflavin and insulin through crosslinked poly(vinyl alcohol)/chitosan blend membrane
Authors: Kim Jin Hong , Kim Ju Young , Lee Young Moo , Kim Kea Yong
Published: April 2003

The permeation of riboflavin and insulin through poly(vinyl alcohol) (PVA) and chitosan blend membrane was conducted. The permeability coefficients of both solutes through the crosslinked PVA and chitosan blend membrane were in the order of 10−6−10−7 cm3 cm/cm2s and showed a pH dependence. The pH‐dependent permeation behavior was discussed in terms of water content and water structure inside of the swollen membrane. Riboflavin and insulin were presumed to permeate through the free water region in the swollen blend membrane. The DSC thermograms of these membranes indicated that the content of free water and the amount of freezing bound water increased with the water content in the membrane. The greater permeation rate of solutes in acidic solution rather than in neutral solution was due to an increase in both water content and the amount of free water and freezing bound water.
Crystallization of fiber‐reinforced poly(phenylene sulfide) composites. I. Experimental studies of crystallization rates and morphology
Authors: Desio Glenn P. , Rebenfeld Ludwig
Published: April 2003

The isothermal crystallization from the melt of unreinforced poly(phenylene sulfide) (PPS) and of model carbon, aramid, and glass‐fiber‐reinforced PPS composites was studied by differential scanning calorimetry and optical microscopy. Crystallization was studied as a function of temperature, and the fiber contents in the composites were varied over a wide range. The results indicate that the influence of fibers on PPS crystallization is not only fiber specific, but also strongly dependent on the surface treatment (size). In general, fiber‐reinforced systems crystallized faster than unreinforced (PPS), and the degree of crystallinity was less under comparable crystallization conditions. It was also observed that the rate of crystallization was enhanced in those systems which exhibited transcrystallinity in thin PPS film/single fiber composites as compared to those systems which did not exhibit transcrystallinity. Furthermore, the degree of crystallinity showed a nonlinear crystallization temperature dependence for those systems that exhibited transcrystallinity.
Structural features of native cellulose gels and films from their susceptibility to enzymic attack
Authors: Beltrame Pier Luigi , Paglia Ernestina Dubini , Seves Alberto , Pellizzoni Elisabetta , Romanò Maria
Published: April 2003

The reaction of enzymic hydrolysis has been used as a probe to evidence the different structural features of bacterial native cellulose gels and films synthesized from different carbon sources. The gels were found to be more hydrolyzable than were the films, both in terms of reaction extent and of initial reaction rate, by factors increasing with temperature. For instance, a cellulose gel synthesized from glucose showed at 50°C a hydrolysis yield twice as much as that of the corresponding film, thus revealing, in the former case, a higher level of substrate accessibility and enzyme penetrability. It has been suggested that the increase of gel accessibility with temperature can be associated with a corresponding lowering of the amount of structured water close to the polymer chains in the gel. The significant decrease of susceptibility to enzymic attack observed in going from the cellulose film obtained from glucose to that obtained from xylose has been related to the markedly lower value of specific surface area estimated in the latter case. Likely, in the film obtained from xylose, densely packed microfibrils occur that are scarcely accessible to enzyme. In some cases, the reaction progress has been followed by SEM analysis. Microcrystalline cellulose has been also considered for comparison.
Single‐Phase blends of polycarbonate and poly(phenyl methacrylate)
Authors: Kyu Thein , Park Dongkyu , Cho Wookap
Published: April 2003

Miscibility studies on blends of polycarbonate (PC) and poly(phenyl methacrylate) (PPMA) were undertaken by means of differential scanning calorimetry (DSC), dynamic mechanical, and dielectric relaxation methods. PC and PPMA were mixed by dissolving in tetrahydrofuran (THE) and subsequently coprecipitated in methanol. DSC studies showed a single glass transition (Tg) that shifts systematically with composition. These Tgs are reproducible in repeated DSC heating cycles, suggesting true miscibility of the pair. The dry PC and PPMA pellets were melt mixed in a Mini‐Mixer/Molder. The extrudates were compression molded. These melt‐mixed PC/PPMA blends exhibited glass like transparency and also showed a single Tg in the DSC scans. The true miscibility of PC and PPMA was further confirmed by dynamic mechnaical and dielectric relaxation methods. The net birefringence has been reduced substantially because of the opposite sign of the itrinsic birefringence of PC and PPMA molecules. At the 12/88 PC/PPMA, the birefringence remains zero at all draw ratios, indicating the achievement of birefringence free polymer alloys.
Polyanhydride microspheres. IV. Morphology and characterization of systems made by spray drying
Authors: Mathiowitz Edith , Bernstein Howard , Giannos Steve , Dor Phillip , Turek Tom , Langer Robert
Published: April 2003

The morphology of bioerodible polyanhydride microspheres produced by spray drying is described. Microspheres prepared from a variety of homo‐ and copolymers were studied and characterized using X‐ray powder diffraction, differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). Crystalline polymers, such as poly(sebacic anhydride) (P(SA)) and poly(fumaric acid) (P(FA)), yielded microspheres with a crenelated and porous surface, as judged by SEM. Polymers, with lower crystallinity, such as copolymers of carboxyphenoxypropane and sebacic acid P(CPP‐SA), yielded microspheres with a smooth external surface. Polymer crystallinity decreased after spray drying, for both blank and drug loaded microspheres.
Free‐radical polymerization of methyl methacrylate initiated by thiol alone
Authors: Xia P. , Cheng H. , Yan D.
Published: April 2003

Three different alkyl thiols, i.e., n‐propylthiol, isopropylthiol, and 2‐methyl‐2‐undecanethio1, were proved efficient to initiate the polymerization of methyl methacrylate at 40°C. The initial polymerization rate, Rp, increases with increasing thiol concentration but cannot be described by a single‐power law. However, Rp is proportional to 1.3th power of the monomer concentration, indicating the participation of monomer in the initiation reaction. With increase of the polarity of solvents, Rp decreases, demonstrating the polar property of the initiating intermediate. The apparent activation energy of overall polymerization was calculated to be 9.3 kcal/mol. Molecular weight measurements indicated the twofold function of the thiol as both an initiator and a regulator.
Thermal behavior and laser marking of a novel nematic liquid crystalline polymer
Authors: Kuder J. E. , Yoon H. N. , DeMartino R. N.
Published: April 2003

The thermal behavior and laser marking of a novel nematic liquid crystalline polymer is explored in this report. The glass transition and mesophase transition temperatures of this material are at 45 and 68°C, respectively, and allow the ready annealing of the nematic phase as well as conversion of the nematic to the isotropic phase by pulsed laser irradiation of metallized or dyed films of the polymer.
Calculation of reactivity ratio of resin copolymers derived from substituted acetophenones using Kelen–Tüdos equation
Authors: Nayak P. L. , Lenka S. , Nayak P. K.
Published: April 2003

A number of resin copolymers have been prepared by condensing some substituted acetophenones with chloro‐substituted anilines, benzoic acids, and formaldehyde. The reactivity ratios of the monomers have been computed by using the Kelen–Tüdos equation. The results have been discussed taking into account the inductive, resonance, and steric effects of the substituents.
Effects of the organometallic coupling agents on adhesion of the carbon fiber–BMI composites
Authors: Chou S. , Chen H.‐C. , Lee K.‐S.
Published: April 2003

In order to increase the chemical bonding force between fiber and resin, several kinds of organometallic coupling agent (such as titanate, zirconate, and zircoaluminate) were chosen and added in the BMI resin formulation, which possess the same solvent system with those coupling agents. The DSC analysis technique was used to find the best curing condition, and TGA was used to investigate the thermal stability property of the best curing condition. For the purpose of analyzing the bonding structure, ESCA surface element analysis techniques was applied in this study. Beside that, the mechanical properties of tensile, flexural, and short‐beam shear strengths were measured for the effect of adding coupling agents, and the SEM of fracture surfaces were taken to study the fractural analysis. The results showed that composites with the application of organometallic coupling agents of [RO–Ti(OX–R′NH2)3] structure in the treatment of BMI resin were highly thermal stable. Also, it was shown that the mechanical strengths of composites fabricated by pretreatment of the carbon fibers with coupling agents were higher than those fabricated by adding coupling agents in resins, but there was no obvious improvement of mechanical properties with higher concentration of coupling agents. However, the SEM showed that the adhesion between fiber and resin can actually be improved by adding proper amount of coupling agents in the BMI resin formulation.
Mathematical model for a semicontinuous esterification process with recycle between terephthalic acid and ethylene glycol
Authors: Yamada T.
Published: April 2003

A new mathematical model has been derived for a semicontinuous recycle esterification process that consists of two reactors, one has the recycle flow to or from another and the discharge flow of the main flow and another has only recycle flow without the discharge flow. This model can give useful information about the optimum design of a new plant through the predictions of oligomer characteristics such as concentrations of carboxyl and hydroxyl end groups, number‐average molecular weight, number‐average degree of polymerization, esterification and saponification degree, diethylene glycol content, melting point, concentrations of ethylene glycol and water in the vapor phase, and so on.
Synthesis of graft copolymers of acrylic monomers onto amylose. II. Study of the ceric ion behavior
Authors: Goñi I. , Gurruchaga M. , Vazquez B. , Valero M. , Guzman G. M.
Published: April 2003

A study of the ceric ion consumption during graft polymerization of methyl acrylate (MA), ethyl acrylate (EA), ethyl methacrylate (EMA), and butyl methacrylate (BMA) with amylose was carried out. Grafted acrylic polymers were isolated by the acid hydrolysis method. Weight‐average and number‐average molecular weights were determined by gel permeation chromatography (GPC). The number of grafted chains (mmol) ranged from 8.70 × 10−3 to 12.35 × 10−3 for acrylates and from 3.20 × 10−3 to 6.80 × 10−3 for methacrylates. These results were related to others obtained from the ceric ion consumption studies.
Preparation of hydrophilic polymer networks by post‐curing reaction
Authors: Andreopoulos Andreas G.
Published: April 2003

Hydrophilic gels are a very important class of polymeric materials with extensive applications as biomedical products. The critical properties of hydrogels, such as sorption and desorption, mechanical behavior, swelling properties, etc., are controlled by network characteristics, i.e. degree of crosslinking and the density, distribution and length of crosslinks. Hydrogels prepared by copolymerization of 2‐hydroxyethyl methacrylate (HEMA) with ethylene glycol dimethacrylate (EGDMA) have already been studied in detail. In this work, hydrophilic networks were prepared by crosslinking HEMA with EGDMA, and poly(2‐hydroxy‐ethyl methacrylate) (PHEMA) with diphenylmethane‐4,4′‐diisocyanate (MDI). The swelling properties of both types of networks were studied and the differences in behavior were attributed to the different techniques applied for network formation.
Resistance of barrier elastomers to hazardous organic liquids
Authors: Khinnavar Rajashekhar S. , Aminabhavi Tejraj M.
Published: April 2003

Sorption and transport of several hazardous, organic chemicals into elastomer membranes have been studied using a simple gravimetric method. The Fickian model was used to estimate the diffusion coefficients of the polymer–solvent systems. The Joshi–Astarita model was employed to investigate the concentration–dependence of diffusion coefficients. From a study of the temperature dependence of the transport coefficients, activation parameters for the process of sorption, diffusion, and permeation have been estimated. Furthermore, the sorption results have also been interpreted in terms of the semiquantitative estimates of the kinetic rate constants and other thermodynamic parameters (enthalpy and entropy) of interest.
Chemical modification of silk with aromatic acid anhydrides
Authors: Tsukada M. , Goto Y. , Freddi G. , Shiozaki H.
Published: April 2003

Bombyx mori silk fibers were chemically modified by acylation with aromatic acid anhydrides, such as phthalic and o‐sulfobenzoic anhydrides. We examined the reactivity of these modifying agents toward silk fibers, the physical and thermal properties, and the dyeing behavior with acid and cationic dyes. The o‐sulfobenzoic anhydride was more reactive toward silk fibroin than phthalic anhydride. The amount of both basic and acidic amino acid residues decreased after modification with aromatic acid anhydrides. The moisture regain of silk treated with phthalic anhydride remained almost unchanged, while that of the samples modified with o‐sulfobenzoic anhydride increased linearly as the weight gain increased. Chemically modified silk fabrics showed improved crease recovery behavior, even though phthalic anhydride seemed more effective at comparatively low weight gain. The modification of silk with o‐sulfobenzoic anhydride caused a drastic a reduction of acid dye uptake and enhanced the affinity of silk for cationic dye. Silk fibers did not show any significant change in thermal behavior, regardless of the modification with o‐sulfobenzoic anhydride. Silk fibers modified with phthalic anhydride showed on differential scanning calorimetry (DSC) curves a minor and broad endothermic peak at around 210°C, attributed probably to the breaking of the crosslinks formed between adjacent fibroin molecules.
An XPS study of the surface–bulk compositional differences in siloxane‐containing block copolymers and polymer blends
Authors: Pertsin A. J. , Gorelova M. M. , Levin V. Yu. , Makarova L. I.
Published: April 2003

X‐ray photoelectron spectroscopy (XPS) is used to compare the surface behavior in various binary systems of poly(dimethylsiloxane) with poly(bisphenol A sulfone) and poly(bisphenol A carbonate). All the systems studied show a pronounced surface enrichment in siloxane. At a fixed siloxane concentration in the bulk the lowest extent of surface enrichment is observed in the +eat copolymers, next go the blends of copolymers in homopolymers, and the highest extent of surface enrichment is characteristic of the blends of homopolymers. The blends of two copolymers show an unexpected surface behavior: The addition of minor amounts of a siloxane‐rich copolymer to another copolymer possessing a much lower siloxane content decreases (rather than increases) the surface siloxane concentration of the latter. A microscopic model is suggested to explain the observed surface behavior. The model involves the formation of a “quasi‐two‐dimensional” overlayer of additive's macromolecules on the blend surface, with the macromolecules oriented preferentially parallel to the sample surface.
Effects of particle size on mechanical and impact properties of epoxy resin filled with spherical silica
Authors: Nakamura Yoshinobu , Yamaguchi Miho , Okubo Masayoshi , Matsumoto Tsunetaka
Published: April 2003

Effects of particle size on the mechanical and impact properties of cured epoxy resins are studied. This resin was filled with spherical silica particles prepared by hydrolysis of silicon tetrachloride. Particles were sorted into five kinds of different mean sizes in the range from 6–42 μm. A static flexural and tensile tests and an instrumented Charpy type impact test were carried out. Flexural strength, tensile strength, and impact‐absorbed energy increased with a decrease in the particle size. Fractured surfaces were observed using a scanning electron microscope to clarify the initiation point of fracture.
Effect of oxygen on vinyl acetate polymerization
Authors: Levy L. B. , Hinojosa L.
Published: April 2003

Various conflicting reports in the literature regarding the effect of oxygen on the stability of vinyl acetate (VA) toward polymerization led us to reexamine this topic using both isothermal stability tests and quasi‐adiabatic calorimetry. Both commercial VA stabilized with 5–20 ppm by weight of hydroquinone (HQ) and purified, unstabilized VA exhibit lower stability to thermally initiated polymerization (at 50–120°C) in the presence of oxygen than in its absence. However, when stabilized with 3–5 ppm of HQ, both air‐saturated and oxygen‐free VA exhibit adequate thermal stability at normal transport and storage temperatures (25–50°C). Oxygen destabilization of VA is probably caused by the relatively low stability of VA polyperoxide rather than by the oxidation of acetaldehyde impurity to peroxyacetic acid. The length of VA polymerization induction periods is about −0.4 order in oxygen partial pressure.
Preparation and mechanical properties of chemically cross‐linked hydroxypropyl cellulose solid films retaining cholesteric liquid crystalline order
Authors: Suto Shinichi , Tashiro Hiroshi , Karasawa Mikio
Published: April 2003

Hydroxypropyl cellulose films were cast from liquid crystalline solutions with a crosslinking agent. The solubility test and the optical measurements of the resultant films were performed. The tensile, dynamic mechanical, and creep properties of the films were determined. The data of solubility in water determined that the cast films are cross‐linked, and the data of circular dichroism spectra, that the cast films retain the cholesteric liquid crystalline order (right‐handed sense). Both findings clarified that the cast films retain the cholesteric order fixed by cross‐linking. The cross‐linking depended on the pairs of the solvent–cross‐linking agent. The mechanical properties also depended on the pairs: the tensile strength and moduli did not always increase with cross‐linking. The creep resistance improved with cross‐linking. The thermally activated Eyring process could be applied and the activated volumes were evaluated for water‐ and methanol‐cast films. There were not clear phenomenological correlations between the mechanical properties of our films.
Transition‐metal coordination for complexing poly‐(vinyl chloride)–polyurethane blends
Authors: Al‐Salah Hasan A. , Al‐Raheil Ismail A.
Published: April 2003

Binary blends of poly(vinyl chloride) (PVC) and polyether polyurethane (PU) containing divalent transition metal (Zn2+) have been prepared by solution blending. The physical and mechanical properties of the blends are studied utilizing differential scanning calorimetry (DSC), thermogravimetry (TG), and tensile testing. The DSC results showed a high degree of molecular mixing of the two polymers. The glass transition temperatures (Tg) of the blends exhibited one major Tg whose position on the temperature scale is raised with increasing levels of PVC. The blends yielded stress–strain behavior similar to reinforced elastomers at low PVC, but at high PVC contents, they exhibited increased elongation. The latter materials showed well‐developed yield points, stress whitening, and necking. Cold drawing was exhibited by the materials under tension. The tensile strength and Young's modulus were enhanced as the PVC content was increased.
Analysis of crosslinking in amine‐cured epoxy systems: The one‐to‐one relationship between Tg and conversion
Authors: Wang Xiaorong , Gillham John K.
Published: April 2003

Network formation, in a system such as a tetrafunctional aromatic diamine cured with a difunctional epoxy, is considered on the basis of only interconnected trifunctional crosslinking sites. The number‐average molecular weight, the crosslinking density, and the gel point, and also the vitrification contours of the time—temperature—transformation (TTT) isothermal cure diagram, are related to the ratio of the reaction rate constants, k2/k1, of the competing reactions of epoxy with secondary amine group (k1) and with primary amine group (k1). It is considered that the glass transition temperature, Tg, is related uniquely to conversion on the basis that the number‐average molecular weight and crosslinking density are insensitive to the ratio, k2/k1. Experimental data support the theoretical result. The potential influences of chemical structure and physical aging on Tg are discussed. © 1992 John Wiley & Sons, Inc.
Recovery of uranium from seawater. XII. Preparation and characterization of lightly crosslinked highly porous chelating resins containing amidoxime groups
Authors: Egawa Hiroaki , Kabay Nalan , Shuto Taketomi , Jyo Akinori
Published: April 2003

A number of lightly cross‐linked poly(acrylonitrile‐co‐divinylbenzene) beads (RN‐5) have been synthesized by suspension polymerization. The use of solvating diluents such as chloroform, dichloroethane, and tetrachloroethane resulted in copolymer beads having highly porous structures. The chelating resins containing amidoxime as a functional group (RNH‐5) have been prepared by the reaction of copolymer beads with 3% hydroxylamine in methanol. A detailed analysis is made of the pore structure of lightly cross‐linked copolymers of acrylonitrile–divinylbenzene and their amidoxime derivatives in the anhydrous state including pore‐size distribution, specific surface area, and pore structure in the aqueous media by means of gel permeation chromatography (GPC). A set of experiments have been performed to ascertain the potential of the resins for the adsorption of uranium from seawater. Because of their modified pore structures, the chelating resins exhibited a marked adsorption rate for uranium in seawater as high as 23 μg of U/cm3 of resin/day without alkaline treatment.
Surface properties of graft copolymers surfactants: Behavior at the water/toluene interface
Authors: Lucas E. F. , Oliveira C. M. , Gomes A. S.
Published: April 2003

Poly(propylene oxide‐b‐ethylene oxide) (PPOPEO) surfactant has been used as a surface tension modifier. In this study, the graft copolymer made of poly(methyl methacrylate) (PMMA) main chain and PPOPEO graft chain behavior at water/toluene interface was observed. Interfacial tension measurements were conducted by dissolving the graft copolymer in toluene at a concentration range 1 wt % −0.0003. The results confirmed the surfactant behavior of graft copolymers, which presented a PMMA/PPOPEO ratio dependence. The critical micellar concentration (CMC) was observed. Above the CMC, the graft copolymers tend to form a monomolecular association that depends upon copolymer molecular weight. © 1992 John Wiley & Sons, Inc.
Reaction kinetics and TTT cure diagrams for off‐stoichiometric ratios of a high‐Tg epoxy/amine system
Authors: Simon S. L. , Gillham J. K.
Published: April 2003

The cure behavior of two off‐stoichiometric ratios, one amine‐rich and the other epoxy‐rich, of a high‐Tg aromatic difunctional epoxy/aromatic tetrafunctional diamine system are studied using differential scanning calorimetry (DSC). The curing reactions are presumed to consist of competing epoxy/amine reactions and a subsequent reaction of epoxy with hydroxyl, termed etherification, that is significant in the epoxy‐rich system after depletion of amino hydrogens. A one‐to‐one relationship between conversion and Tg independent of cure temperature is found for each of the off‐stoichiometric systems in spite of the competing reactions. Since it is uniquely related to fractional conversion, sensitive, and easily measured, Tg is used to monitor the curing reactions. Kinetically controlled master curves for isothermal cure are obtained for each system by shifting Tg vs. In time data to an arbitrary reference temperature; apparent activation energies for the epoxy/amine and the etherification reaction regimes appear to be identical at 15.5 kcal/mol. Experimental DSC data are satisfactorily described for both systems by a kinetic model of the competitive epoxy/amine and etherification reactions. The ratio of the rate constants for the reactions of epoxy with the secondary amine group and epoxy with the primary amine group, α = k2/k1, is found to be approximately 0.5 (i.e., equal reactivity of amino hydrogens), whereas the ratio of the rate constants for the reactions of epoxy with hydroxyl and epoxy with the primary amine group, β = k3/k1, is found to be 0.001. Diffusion control is incorporated in the model by the use of a free‐volume theory. Vitrification and iso‐Tg contours in the time–temperature–transformation (TTT) isothermal‐cure diagram are calculated for both systems from the kinetic model. © 1992 John Wiley & Sons, Inc.
In‐plane solvent diffusion in a photosensitive polyimide
Authors: Shih Da‐Yuan , Nunes Sharon , Paraszczak Jurij , Galligan Eileen , Cataldo John , Serino Russell
Published: April 2003

The diffusion of an organic solvent,N‐methylpyrollidinone (NMP), in a fully imidized photosensitive polyimide, 4,4′‐benzophenone tetracarboxylic dianhydride (BTDA–tMDA), was investigated. The polyimide (PI) films were prepared by spin‐coating, soft‐bake, deep UV exposure, and final‐baked to a peak temperature ranging from 230 to 375°C. The thickness of the final films is approximately 5.0 μm. Patterned metal was then electronbeam‐evaporated through a molybdenum shadow mask over the PI surface. The rate of lateral (in‐plane) diffusion of NMP in the PI covered with metal follows Fick's\documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt t $\end{document}relationship over a temperature range of 40–85°C. The rate of diffusion was shown to increase with increasing NMP temperatures, typical of a thermal‐activated process. The diffusion coefficients, as measured by the solvent penetration distance as a function of the square root of time, were found to obey the Arrhenius equation:D=D0× exp(−Q/RT) cm2/s, where the frequency factor,D0, ranges from 0.0015 to 0.0045 cm2/s, and the activation energy,Q, ranges from 5.52–6.34 kcal/mol. BothD0andQdecrease with increasing PI baking temperatures. © 1992 John Wiley & Sons, Inc.
Increased breakdown strengths of polypropylene films melt‐extruded from plasma‐treated resin
Authors: Mammone Robert J. , William L. Wade  , Binder Michael
Published: April 2003

Thin (11–36 μm) films formed by melt extruding polypropylene resin after the resin had been briefly exposed to low pressure, low temperature, 96% CF4/4% O2 gas plasma, exhibited approximately a 20% increase in dielectric breakdown strength. © 1992 John Wiley & Sons, Inc.
A study of polyindole perchlorate (PIP) prepared by electropolymerization
Authors: Choi Kyung Moon , Jang Joon Ho , Rhee Hee‐Woo , Kim Keu Hong
Published: April 2003

Polyindole perchlorate (PIP) was obtained by electrochemical oxidation using a potential of 0.7 V as anodic precipitates. A cyclic voltammetry was performed in acetonitrile solution containing 0.2M indole and 0.1M tetraethylammonium perchlorate. The result suggested that this electrode reaction was reversible, and the peak width (ΔEp) of the anodic and cathodic peaks obtained was 58 mV. The result of IR measurements clarified that the polyindole was obtained by a 1,3‐polymerized mechanism. As for the ESCA analysis of the PIP pellet, besides a main N1s peak at 399.6 eV, a high binding energy peak at 402.3 eV was observed. Also, in the case of the C1s peak, besides a main peak at 284.6 eV, a shoulder peak at high binding energy was measured. These results suggested that an electropolymerization of indole was performed by the formation of radical cations. A thermogravimetric analysis was performed in a temperature range from 25 to 800°C. The rate of thermal decomposition (R) for the polyindole‐and polyaniline‐based polymers was calculated by a computer connected with a thermal analyzer. From the thermal analysis, it was concluded that the polyindole‐based polymers decomposed at higher temperatures than did the polyaniline‐based samples. The Rmax values of the polyindole systems were not related to the kind of dopants, but in the case of the polyaniline systems, they were seriously affected by the kind of electron acceptors. The electrical conductivity of the PIP pellet was performed in a temperature range from 150 to 25°C. The values of log σ at 25°C and Ea obtained were ‐1.63 s/cm and 0.508 eV, respectively. From the results, we suggested that a possible conduction mechanism and charge carriers for the PIP pellet were hopping conduction and polarons, respectively. The ESR measurements for the PIP powder were performed at room temperature, and the values of various ESR parameters were calculated. © 1992 John Wiley & Sons, Inc.
Polyurethane elastomers based on molecular weight advanced poly(ethylene ether carbonate) polyols. IV. Effects of poly(propylene glycol) modified diols
Authors: Harris Robert F. , Joseph Michael D. , Davidson Carla
Published: April 2003

A series of polyurethane elastomers with a (A{BC}m)n type of structure have been prepared and characterized based on poly(propylene glycol) modified poly(ethylene ether carbonate) polyols, where the poly(propylene glycol) content and block length were varied systematically. Strength and modulus properties showed a marked dependence on modifier level and exhibited synergistic property improvements at 25–50 wt % modifier, relative to both unmodified poly(ethylene ether carbonate) diol and poly(propylene glycol) controls. DMA results indicated an increased modulus for the modified plaques throughout the rubbery plateau region, with higher thermal dissociation temperatures. Excellent organic solvent resistance was maintained with 25–50 wt % poly(propylene glycol) modification in the soft segment. Chemical structure of the polyurethane elastomers was established by proton and 13C‐NMR spectroscopy. The morphology of these modified polyurethanes appears to be quite complex. Since the modified soft segments are block copolymers of blocks with a tendency toward immiscibility, some microphase separation within the soft segment domains of the polyurethane polymers might be expected. The soft segment Tg is highest where properties are maximized, suggesting changes in phase mixing. © 1992 John Wiley & Sons, Inc.
Preparation of polymer–ceramic composite membranes with thin defect‐free separating layers
Authors: Rezac M. E. , Koros W. J.
Published: April 2003

Polymer—ceramic composite membranes with essentially defect‐free separating layers have been prepared by a solution deposition technique. Rigid polymers were used for the selective organic layer. These included high molecular weight samples of 5,5′‐[2,2,2‐trifluoro‐1‐(trifluoromethyl)ethylidene]bis‐1,3‐isobenzofuran‐dione, isopropylidenedianiline (6FDA‐IPDA), 5,5′‐[2,2,2‐trifluoro‐1‐(trifluoromethyl)ethylidene]bis‐1,3‐isobenzofuran‐dione, methylenedianiline (6FDA‐MDA), tetramethylhexafluorobisphenol‐A polycarbonate (TMHFPC), and tetramethylhexafluoropolysulfone (TMHFPSF). Attempts to prepare composite membranes from lower molecular weight samples of bisphenol‐A polycarbonate (PC) and tetrabromohexafluorobisphenol‐A polycarbonate (TBHFPC) were unsuccessful. The PC and TBHFPC composites exhibited a decrease in the measured gas flux after polymer deposition; however, the selectivities of the composites were considerably less than that of a dense film of the same materials. A microporous ceramic membrane prepared by Anotec Separations was used as the support layer. This ceramic membrane provided minimal resistance to gas flow. The selective composite membranes were found to have high gas fluxes and gas separating abilities essentially equivalent to that of a dense isotropic film. The estimated, effective skin layer thicknesses for these membranes are on the order of 1500 Å to 1.0 μm. The formation of these composites is believed to occur through a sieving process in which large swollen polymer chains are sieved out of solution by the ceramic support. Polymer solutions that had swollen coil diameters that were smaller than that of the ceramic membrane did not produce selective composite membranes, while those solutions with swollen coil diameter that were larger than that of the ceramic membrane produced defect‐free polymer layers. © 1992 John Wiley & Sons, Inc.
Immobilization of enzymes on electrostatic medium of positively charged dimethylamino nylon gel
Authors: Kobayashi Takaomi , Miyama Hajime , Kawata Souji , Nosaka Yoshio , Fujii Nobuyuki
Published: April 2003

Urease and glucose oxidase were immobilized by positively charged nylon gel matrix made from dimethylaminated nylon. The stability of the immobilized enzyme after preheating and incubation in organic solvent were measured and compared with that of native enzymes. Also, pH dependency of the immobilized enzymes was examined. The pH activity curves of the immobilized enzyme shift toward a low pH compared with that of the native enzyme. Using the pH difference, the electrostatic potential of the positively charged nylon gel was estimated. The estimated values of the positively charged gel were +90 and +102 mV for the immobilized urease and immobilized glucose oxidase, respectively. In the presence of buffer salt, they decreased to +30 and +24 mV, respectively. © 1992 John Wiley & Sons, Inc.
Thermodynamic modeling of the sorption of organic chemicals in thermoplastics and elastomers
Authors: Park Jae K. , Bontoux Laurent
Published: April 2003

The amount of solute sorbed per unit weight of sorbent, qe, and the equilibrium solubility (partition) coefficient were measured using a gravimetric method for various types of organic chemicals in thermoplastics and elastomers. A thermodynamic model was derived to predict the activity‐dependent partition coefficient and qe for a wide range of organic chemicals. The thermodynamic model produced a better fit to the measured qe values than did the Flory–Huggins equation. Partition coefficients and qe increased with increase in activity. For nonpolar compounds, qe increased logarithmically but decreased for polar compounds with an increase in the saturation organic chemical vapor concentration. Elastomers had 14–28 times greater qe values than did thermoplastics. A structure–activity relationship was found to accurately predict the partition coefficient for liphophilic organic chemicals at a specific activity. © 1993 John Wiley & Sons, Inc.
Polymers from renewable resources. I. Castor oil‐based interpenetrating polymer networks: Thermal and mechanical properties
Authors: Nayak Padma L. , Lenka S. , Panda Santosh K. , Pattnaik T.
Published: April 2003

A number of polyurethanes (PUs) were synthesized by reacting castor oil with toluene‐2,4‐diisocyanate and hexamethylene diisocyanate and varying the NCO/OH ratio. All these polyurethanes were reacted with some acrylic monomers like ethyl acrylate, n‐butyl acrylate, ethyl methacrylate, and butyl methacrylate using a crosslinker ethylene glycol dimethyl‐acrylate and benzoyl peroxide as the initiator. The physicochemical properties of interpenetrating polymer networks (IPNs) are reported. Thermogravimetric analysis was used to study the thermal behavior of IPNs and the evaluation of kinetic parameters. Degradation mechanism has also been investigated. Some of the mechanical properties viz. tensile strength, shore‐A hardness, elongation at break, etc. are also reported. © 1993 John Wiley & Sons, Inc.
Co[poly(ethylene terephthalate‐p‐oxybenzoate)] thermotropic copolyester. II. X‐ray diffraction analysis
Authors: Shinn Ted‐Hong , Lin Chen‐Chong
Published: April 2003

A series of co[poly(ethylene terephthalate‐p‐oxybenzoate)] thermotropic copolyester with different compositions were prepared by the copolymerization of either poly(ethylene terephthalate) (PET) polymer or its oligomer with p‐acetoxy‐benzoic acid. The polymeric products were subjected to solid‐state polymerization for various time intervals. Effects of composition ratio and solid‐state polymerization time on X‐ray diffraction behavior were investigated. It is found that the effect of transesterification induced by solid‐state polymerization causes an increase in crystallinity with the copolyesters having high mol % of p‐oxybenzoic acid (POB) moiety and causes a decrease in crystallinity with the copolyesters having high mol % of PET moiety. In general, the crystallinity of copolyesters is first increased and then decreased as solid‐state polymerization time proceeds. However, the crystallinity of copolyester having POB/PET = 80/20 composition is increased generally at 4‐h solid‐state polymerization. It is also found that the crystallinity of copolyesters is decreased by quenching. The copolyester based upon either PET oligomer with 4‐h solid‐state polymerization or PET polymer with 8‐h solid‐state polymerization shows the most similar X‐ray diffraction pattern with that of Eastman 10109. © 1993 John Wiley & Sons, Inc.
Properties of polyamic acid ionomers
Authors: Yu Xuehai , Grady Brian P. , Reiner Richard S. , Cooper S. L.
Published: April 2003

Polymers containing amic acid units were produced by reacting an oligomer based on polytetramethylene oxide (PTMO) with 1,2,4,5‐benzenetetracarboxylic dianhydride (BTDA). Neutralization by a metal salt produced amic acid ionomers. Similar to other ionomer systems, neutralization from the acid to the ionomer led to the formation of a separate ionic phase as determined by dynamic mechanical analysis. Phase separation resulted in a substantial increase in mechanical properties. The effect of neutralization level, cation, soft‐segment molecular weight, and soft‐segment end group on mechanical and thermal properties was investigated. © 1993 John Wiley & Sons, Inc.
Graft copolymerization of starch with methyl acrylate: An examination of reaction variables
Authors: Patil Damodar R. , Fanta George F.
Published: April 2003

Starch‐g‐poly(methyl acrylate) (S‐g‐PMA) copolymers containing 55–60% PMA were prepared from cornstarch, high amylose cornstarch, and waxy cornstarch with ceric ammonium nitrate initiation. Graft copolymers were characterized with respect to % PMA homopolymer, % conversion of monomer to polymer, grafted PMA content, grafting frequency, and the molecular weight and molecular weight distributions of PMA grafts. Variables investigated in the graft copolymerization reaction were nitric acid concentration, ceric ion‐to‐starch ratio, reaction time, gelatinization of the starch, and reactant concentration in water. At high reactant concentrations, high conversions of methyl acrylate to grafted PMA could be obtained in less than 0.5 h at 25°C. © 1993 John Wiley & Sons, Inc.
Polystyrene–gelatin composites prepared via a gel pathway
Authors: Ruckenstein E. , Xu G.
Published: April 2003

Composite polymers of polystyrene and gelatin have been prepared using a gel pathway. The gels have been obtained by mixing at 50°C an aqueous solution containing gelatin and a surfactant (SDS) with styrene containing an initiator (AIBN). The obtained emulsions have the appearance of gels and are very stable both at room temperature and at 50°C. At 50°C, these gels are liquidlike with high viscosity; at room temperature, solidlike gels are formed when the gelatin content is sufficiently high. Polymerization of the gels can be achieved in several days at room temperature and in 24 h at 50°C. Composite polymers with different water‐absorbing capacities have been produced by controlling the polymerization temperature and duration. These composite polymers are insoluble in water, ethanol, octane, and cyclohexane, but exhibit some swelling in these liquids. Additional thermal treatment at relatively high temperatures increases the mechanical strength of the composites. © 1993 John Wiley & Sons, Inc.