bluuebunny/crossref_metadata_2025_split huggingface dataset:
Photooxidative effects on properties and structure of high‐density polyethylene
Authors: Jabarin Saleh A. , Lofgren Elizabeth A. 
Published: April 2003

AbstractThe environmental degradation of high‐density polyethylene (HDPE) has been studied, in addition to that of HDPE blends, containing various concentrations of ethylene carbon monoxide copolymer. Extruded sheets of each material were exposed to natural Arizona sunlight for times up to 6 months. Exposed samples were then analyzed with respect to molecular weight, density, thermal behavior, mechanical properties, and infrared absorption. Additional samples were exposed to laboratory weathering conditions, evaluated in terms of property changes, melted, reformed, and then reevaluated without further weathering exposure. Results indicate that sunlight exposure causes decreased elongation to break, increased embrittlement, decreased molecular weight, and increased crystallinity. Environmental oxidative degradation is elucidated by the measurement of specific infrared bands, sensitive to the formation of carbonyl and vinyl end groups. As environmental degradation causes reductions of molecular weight, polymer chain mobility increases, leading to a higher degree of crystallinity. This increased crystallinity, along with the decreased molecular weight, accounts for the loss of ductility, indicated by a sharp decrease in ultimate elongation. The presence of carbon monoxide copolymer in the blended samples accelerates the process of environmental degradation, however, the degradation mechanisms appear to be similar to those observed for nonblended HDPE. © 1994 John Wiley & Sons, Inc.
Miscible blends of polybenzimidazole and polyaramides with polyvinylpyrrolidone
Authors: Cherdron H. , Haubs M. , Herold F. , Schneller A. , Herrmann‐Schönherr O. , Wagener R. 
Published: April 2003

AbstractThe blend behavior of polybenzimidazole and a series of polyaramides with polyvinylpyrrolidone is presented. Regardless of their chemical structure, all systems showed miscible blends over the composition range investigated. This may offer the opportunity to extend the application range of these basically structural materials into the area of functional polymers. Especially in membranes, the addition of the highly hydrophilic polyvinylpyrrolidone leads to a considerable increase in performance, i.e., in flux and antifouling behavior. © 1994 John Wiley & Sons, Inc.
Comparison of some butadiene‐based impact modifiers for polycarbonate
Authors: Cheng C. , Peduto N. , Hiltner A. , Baer E. , Soskey P. R. , Mylonakis S. G. 
Published: April 2003

AbstractThe relationship of blend morphology to deformation mechanisms and notched Izod impact strength was studied with three butadiene‐based impact modifiers for polycarbonate (PC). The impact modifiers were a linear polybutadiene (PB), a styrene–butadiene–styrene block copolymer (SBS), and a structured latex particle having a PB core and methyl methacrylate/styrene shell (MBS). The particle‐size distribution in the blends was determined from transmission electron micrographs (TEM). Fractographic analysis combined with TEM examination of thin sections from impacted specimens provided insight into the failure mechanisms. Good impact was achieved with PC/MBS blends when cavitation of the core–shell particles relieved triaxiality and enabled the matrix to fracture by the plane stress ductile tearing mode that is characteristic of thin PC. The best impact properties were obtained with PC/SBS blends when the modifier was dispersed as aggregates of small particles. Cavitation at the weak internal boundaries relieved triaxiality, but subsequent coalescence of cavitated particles during ductile drawing of the matrix created critical size voids and the resulting secondary cracks reduced the toughness of the blend. In general, PB did not significantly enhance the impact strength of PC. © 1994 John Wiley & Sons, Inc.
Fabrication of composite hollow fibers for air separation
Authors: Chung Tai‐Shung , Kafchinski E. Ronald , Kohn Rachel S. , Foley Paul , Straff Ritchie S. 
Published: April 2003

AbstractBy using microporous polyacrylonitrile (PAN) hollow fibers as the substrate, we developed two types of composite fibers for air‐separation. One was a poly(4‐vinyl pyridine) (4‐PVP)/(hexafluoro propane dianhydride)–durene (6FDA)/PAN composite hollow fiber, and the other was a 6FDA–3,5‐diaminobenzonitrile/6FDA–durene/PAN composite hollow fiber. The asymmetric PAN fiber was prepared using dry‐jet wet‐spinning technology, and the deposition of a thin gutter layer of 6FDA–durene on PAN was carried out by prewetting PAN fibers with Fluorinert® before solution coating. The topcoating of a thin layer (200–300 Å) of PVP or 6FDA–3,5‐diaminobenzonitrile on PAN/6FDA–durene fibers was conducted using a conventional solution coating method. The selectivity of 0.7% 4‐PVP/2% 6F–durene/PAN composite fibers for O2/N2 was 5.6 with an O2 permeance of 32.2 × 10−6 cc(STP)/cm2 s cmHg, whereas the selectivity of 0.5% 6FDA–3,5‐diaminobenzonitrile/2% 6F–durene/PAN fibers was 5.1 with an O2 permeance greater than 37.2 × 10−6 cc(STP)/cm2 s cmHg. Both fiber selectivities can be further improved by increasing the thicknesses of the selective layer. © 1994 John Wiley & Sons, Inc.
Classification of nylon 66 impurities using digital image processing
Authors: Brasington Chandis R. , Gadala‐Maria F. 
Published: April 2003

AbstractColor image processing was used to classify the impurities in nylon 66 that fluoresce when exposed to ultraviolet light. The hue value determined from digitized color images was found to correlate well to the color of the fluorescence as seen by the naked eye. Digital image processing is advantageous over visual observation because it removes the subjectivity from the classification process, and is a relatively simple and inexpensive method compared to other spectroscopic techniques. The hue values of the impurities may provide a quantitative data base that could lead to process improvements. © 1994 John Wiley & Sons, Inc.
Macromolecular systems in heat‐resistant drilling fluids; advantages of gels on linear polymers
Authors: Collette C. , Lafuma F. , Audebert R. , Brouard R. 
Published: April 2003

AbstractThe degradation process of linear water‐soluble vinyl polymers was followed in aqueous medium at temperatures higher than 150°C. We found that, for any chemical structure, thermal oxidative degradation of the longest chains always occurs, leading to moieties of lower molecular weight (20,000–60,000). The behavior of swollen tridimensionnal networks was tested under the same conditions, and it appeared that rheological and fluid loss properties of the system could be maintained in that case for an optimum number of crosslinks. The corresponding gels were used in simple formulations containing some other drilling fluid components. The first results concerning the thermal stability of the latter are very encouraging. © 1994 John Wiley & Sons, Inc.
Monoepoxy polymerization initiated by BF3‐amine complexes in bulk. II. Influence of water and by‐products on polymer formation
Authors: Chabanne Philippe , Tighzert Lan , Pascault Jean‐Pierre 
Published: April 2003

AbstractThe polymerization of a monoepoxy, phenylglycidylether (PGE), initiated by BF3‐4‐methoxyaniline (BF3‐4MA) was studied at 60°C. The polymerization rate was found to be Rp = kp [BF3‐4MA]0.53 [PGE]. The improper fraction of BF3‐4MA shows the complexity of the polymerization mechanism. Moreover, the influence of water, temperature, by‐products formed during the polymerization, on the kinetics of PGE was also examined. Furthermore, two other monoepoxy monomers, glycidylmethacrylate (GMA) and α‐napthylglycidylether (NGE), were studied for the comparison with PGE. Finally, an overall mechanism of the cationic polymerization of epoxy by BF3‐amine complex was proposed. © 1994 John Wiley & Sons, Inc.
Propylene polymerization in slurry catalyzed by titanium trichloride–diethyl aluminum chloride
Authors: Kahraman R. , Erdoğan M. , Bilgiç T. , Savaşçi Ö. T. 
Published: April 2003

AbstractPropylene is polymerized in a slurry over a TiCl3 · ⅓AlCl3 catalyst with a DEAC cocatalyst, approaching conditions of industrial relevance. The effects of various parameters such as temperature, pressure, cocatalyst‐to‐catalyst ratio, hydrogen concentration, and polymerization time are investigated with particular emphasis on the yield, tacticity, molecular weight, bulk density, and particle size of the resulting polymer. The highest yield and isotactic content are obtained at an Al/Ti ratio of 6, temperature of 70°C, and pressure of 9 kg/cm2g. The polymerization rate is found to be first order up to a monomer concentration of 2.5 mol/L. The overall activation energy of polymerization calculated from an Arrhenius plot is found to be 11.6 kcal/mol. A correlation between MFI and molecular weight is also presented. © 1994 John Wiley & Sons, Inc.
Polymeric phosphonium salts as a novel class of cationic biocides. VII. Synthesis and antibacterial activity of polymeric phosphonium salts and their model compounds containing long alkyl chains
Authors: Kanazawa Akihiko , Ikeda Tomiki , Endo Takeshi 
Published: April 2003

AbstractVarious polymeric phosphonium salts containing long alkyl chains (C10C18) and their corresponding model compounds were prepared, which possess the same hydrophobic structure as that of the common disinfectants (quaternary ammonium salts), and their antibacterial activities were evaluated by means of the viable cell counting method against Staphylococcus aureus (Gram‐positive) and Escherichia coli (Gram‐negative). The polymer with the decyl group exhibited a higher activity than that of the corresponding model compound, particularly against the Gram‐positive strain. Furthermore, antibacterial activity of the polymers was found to decrease as the chain length increased. In contrast with the polymers, the antibacterial activity of the corresponding model compounds increased as hydrophobicity of the substituents increased. The antibacterial activity was strongly dependent on the structure, particularly on the length of the alkyl chain. © 1994 John Wiley & Sons, Inc.
Structure–property relationship in copolymers of methacrylic acid esters. I. Thermal behavior
Authors: Agarwal Seema , Choudhary Veena , Varma I. K. 
Published: April 2003

AbstractThis article describes the synthesis and thermal characterization of copolymers of methyl methacrylate (MMA) and alkyl methacrylates. The copolymerization was carried out using different mol fractions (0.05–0.25) of alkyl methacrylates, i.e., octyl methacrylate (OMA)/decyl methacrylate (DMA)/lauryl methacrylate (LMA)/stearyl methacrylate (SMA), in the initial feed at 80°C. The copolymer composition was determined from 1H‐NMR. The thermal stability of the copolymers was investigated by thermogravimetric analysis and pyrolysis gas chromatography. A two/three‐step degradation was observed in the copolymer samples. The monomers were the major product of degradation in most of the copolymers except in SMA/MMA copolymers where the product of side‐group elimination was also observed. An attempt was also made to determine the yield of the monomers during degradation and then to evaluate the copolymer composition. © 1994 John Wiley & Sons, Inc.
Synthesis and water absorbency of the copolymer of acrylamide with anionic monomers
Authors: Yao Ke‐Jun , Zhou Wen‐Jing 
Published: April 2003

AbstractA series of novel copolymer superabsorbents based on acrylamide, sodium allylsulfonate, sodium acrylate, andN,N′‐methylenebisacrylamide were prepared by copolymerization. The resulting superabsorbents have a fast swelling rate. The experimental results show that absorbency increases to a maximum as the cross‐linking increases, but an excess of cross‐linking leads to a swelling decrease. Their water retention was observed at pressures of 1–10 kg/cm2and temperatures of 60 and 100°C, respectively. The water retention of soil has been enhanced by using the poly(acrylamide–sodium allysulfonate–sodium acrylate) superabsorbent; its use for bean growth was also investigated. © 1994 John Wiley & Sons, Inc.
Cross‐linking poly(ethylene oxide) and poly[oxymethylene‐oligo(oxyethylene)] with ultraviolet radiation
Authors: Sloop Steven E. , Lerner Michael M. , Stephens Thomas S. , Tipton Andrew L. , Paull Deborah G. , Stenger‐Smith John D. 
Published: April 2003

AbstractPoly(ethylene oxide) (PEO) and poly[oxymethylene‐oligo(oxyethylene)] (PEM) disks are cross‐linked by exposure to 254 nm radiation. The rate of formation of cross‐links is greatly enhanced by the presence of benzophenone, and an average cross‐link density of up to 6 mol % of ethoxy units can be obtained after several hours of irradiation. The highly cross‐linked polymers are insoluble in water or organic solvents and show improved physical properties for handling and the formation of free‐standing films. Scanning calorimetry and polymer swelling are employed to characterize the polymers, and impedance measurements are reported for sodium salt complexes prepared from the cross‐linked polymers. Dynamic modulus measurements show that, upon irradiation, PEO and PEM become cross‐linked, elastomeric solids. © 1994 John Wiley & Sons, Inc.
Hydrolytic degradation of ionically cross‐linked polyphosphazene microspheres
Authors: Andrianov Alexander K. , Payne Lendon G. , Visscher Karyn B. , Allcock Harry R. , Langer Robert 
Published: April 2003

AbstractThe hydrolytic degradation of gel microspheres based on calcium cross‐linked phosphazene polyelectrolytes, poly[di(carboxylatophenoxy)phosphazene] (PCPP) and poly[(carboxylatophenoxy) (glycinato)phosphazene] (PCGPP), was investigated. These microspheres are of importance as carriers in protein and cell encapsulation. Both PCPP and PCGPP ionotropic polyphosphazene hydrogels are degradable in an aqueous environment (pH 7.4, 37°C). The degradation rates can be increased by incorporation of hydrolysis sensitive glycinato groups as the pendant structures in the polymer (PCGPP). Hydrolysis of these polymer hydrogels led to low molecular weight (<1,000 Da) products. The erosion and molecular weight profiles varied also according to the molecular weight of the polyphosphazene constituting the gel beads. Another approach to affect the degradation rates consists of coating microspheres with poly‐L‐lysine. Ionotropic polyphosphazene hydrogels have potential as biodegradable devices for controlled drug delivery systems. © 1994 John Wiley & Sons, Inc.
Solid‐state polymerization vis‐à‐vis fiber formation of step‐growth polymers. I. Results from a study of nylon 66
Authors: Srinivasan Rangarajan , Desai Prashant , Abhiraman A. S. , Knorr Raymond S. 
Published: April 2003

AbstractThis study is directed toward synergistic integration of processing of nylon 66 fibers with solid‐state polymerization. The following two goals are sought through the incorporation of solid‐state polymerization after the initial shaping operation: eliminating some of the processing problems in the production of high molecular weight, high performance industrial fibers and attainment of improved mechanical properties via high molecular weight. Successful solid‐state polymerization has been achieved with as‐spun fibers of nylon 66 and molecular weights up to 280,000 g/mol have been obtained from a starting molecular weight of 40,000 g/mol. It is shown that much of the ductility of the starting fiber can be retained, or even enhanced, with solid‐state polymerization. Simulated drawing experiments using a thermal deformation analysis technique show an increase in the drawing potential of the solid‐state polymerized fiber as compared to the starting material. This has important implications regarding the ultimate properties that can be achieved in fibers of condensation polymers. © 1994 John Wiley & Sons, Inc.
Crystallization and melting behaviors of poly(aryletheretherketone) (PEEK) on origin of double melting peaks
Authors: Bas C. , Battesti P. , Albérola N. D. 
Published: April 2003

AbstractThe crystallization and melting behaviors of poly(aryletheretherketone) (PEEK) films were investigated, using differential scanning calorimetry and metallurgy concepts. The shape of the time–temperature–transformation (TTT) diagram, established for PEEK, results from both nucleation and growth phenomena. The double melting behavior exhibited by isothermally crystallized PEEK samples are discussed through the TTT diagram and the influence of the thermal history in the molten state. The upper melting peak arises first and the lower melting peak is developed later. The location of such a second endotherm is shifted toward the higher temperature with increasing either the crystallization temperature or the annealing time while the location of the upper melting peak seems to be unchanged. The double melting behavior is related to a bimodal distribution in size and/or perfection of lamellae developed in a two‐step crystallization. With increasing temperature and/or annealing time in the molten state, the pattern of the endothermic curves is modified. The observed changes are discussed through two origins: the progressive disappearance of remnants of the former crystals and a thermal degradation leading to a cross‐linking of the polymer. © 1994 John Wiley & Sons, Inc.
Synthesis and characterization of methacrylic acid–ethyl acrylate copolymers
Authors: Bajaj P. , Goyal Meenakshi , Chavan R. B. 
Published: April 2003

AbstractCopolymerization of methacrylic acid (MAA) and ethyl acrylate (EA) was performed in aqueous medium in the presence of an emulsifier with MAA as the major component (53.7–82.3 mol %). Emulsion stability was studied as a function of concentration and the nature of the emulsifier (ionic or nonionic). Copolymers were characterized using IR and 1H‐NMR spectroscopy. 13C‐NMR spectra of MAA–EA copolymers have been discussed in terms of their triad monomer sequence distributions. Reactivity ratios of the MAA–EA pair were determined using a nonlinear least‐square errors in variables method. Partition of the monomers in aqueous and organic phases was studied using a gas chromatographic technique. A two‐loci polymerization mechanism was proposed on the basis of this partition behavior and the calculated composition of the oligomeric radicals formed in the initial stages of polymerization. © 1994 John Wiley & Sons, Inc.
Thermal stability studies of a polyimide–polytetrafluoroethylene blend and its components
Authors: Davis Charles R. , Zimmerman Jeffrey A. 
Published: April 2003

AbstractLow‐dielectric constant (ϵr) polymers, such as polytetrafluoroethylene (PTFE), are an important component of advanced electronic products that transit data, since it is this physical property that largely determines a device's performance. For instance, the dielectric constant determines overall signal speed and proximity in that one circuit line can be placed to another, i.e., wiring density, while maintaining desired electrical characteristics. However, due to PTFE's inertness and intractability, significant challenges exist in the successful application of the polymer as an insulation material. One specific example is the lack of available methods to uniformly and controllably generate fine, high‐density features in the neat fluoropolymer. Recently, it was reported that excellent structuring characteristics of PTFE can be achieved by sensitizing the fluoropolymer to excimer laser radiation using small quantities of an aromatic polyimide. An important physical property of the sensitization agent, in addition to interacting strongly with the laser's emitted energy, is suitable thermal stability due to PTFE's high‐temperature processing requirements. Using multiple analysis techniques, the thermal decomposition behavior of PTFE, polyimide sensitizer, and resulting polymer blend have been evaluated. It was determined that the onset of decomposition for all systems is near or greater than 500°C. © 1994 John Wiley & Sons, Inc.
Thermal analysis of poly(vinylidene fluoride) (PVDF) in composites with polypyrrole (PPy)
Authors: Pawde Sunita , Bhat Narendra 
Published: April 2003

AbstractThe melting behavior and dynamic mechanical properties of poly(vinylidene fluoride) (PVDF) in composites with polypyrrole (PPy) have been investigated using DSC/DTA and a Rheovibron viscoelastometer. Composites with varying percentages of PPy (5–50%) were synthesized using a solution‐casting method with FeCl3 as the oxidant. It was observed that the melting point of PVDF increased as the percent of PPy was increased. A plot of tan δ vs. temperature showed the shift of the α relaxation peak to higher temperature. These results, together with our earlier studies on the basis of XRD and IR, indicate molecular interaction, an antiplasticization effect of PPy, and partial phase transformation of PVDF to phase I (β form). © 1994 John Wiley & Sons, Inc.
Modifying acrylic‐based superabsorbents. I. Modification of crosslinker and comonomer nature
Authors: Omidian H. , Hashemi S. A. , Askari F. , Nafisi S. 
Published: April 2003

AbstractThis article is devoted to the synthesis, characterization, and modification of acrylic‐based superabsorbents which are synthesized by carrying out the well‐known process of inverse suspension polymerization. The dispersion is stabilized by using a mixture of micromolecular and macromolecular stabilizers. High swelling and appropriate absorption kinetics are obtained, provided that parameters (including initial monomer and crosslinker concentration, range of neutralization degree, initiating and stabilizing system, monomer addition rate, temperature and nature of the organic phase) are being considered. Modifications of crosslinker and comonomer nature and their effects on absorbency characteristics (capacity and rate) of the above‐mentioned superabsorbents are graphically presented. Finally, diffusion behavior of superabsorbents is briefly discussed. © 1994 John Wiley & Sons, Inc.
Preparation and properties of polymide foams
Authors: Kashiwame Josho , Ashida Keneyoshi 
Published: April 2003

AbstractCatalysts for the raction of aromatic isocyanates with aromatic anhydrides to form imides were investigated using a model reaction. Alkali metal acetylacetone chelate compounds exhibited good catalytic efficiency and selectivity in dimethyl sulfoxide (DMSO). These catalysts were used for the preparation of polymide foams. The resulting foams exhibited excellent fire resistance and thermal stability. © 1994 John Wiley & Sons, Inc.
Segmented block copolyetheramides based on nylon 6 and polyoxypropylene. I. Synthesis and characterization
Authors: Yu Yeong Chool , Jo Won Ho 
Published: April 2003

AbstractVarious segmented block copolyetheramides based on nylon 6 and polyoxypropylene (POP) were synthesized by melt polymerization of caprolactam (CPL) and polyoxypropylene diamines (POPD) as a function of the size and content of POPD. As the content of POPD in the feed increased, the IR absorption band at 1110 cm−1 increased. The 1H‐NMR analysis indicated that peaks characteristic of methylene groups in POP unit appeared at 1.2, 3.6, and 3.8 ppm. The compositions of the hard and soft segments in the block copolymer were determined from the NMR data. The POP content in copolymer was higher than that in the feed due to the removal of unreacted CPL by water extraction. The average block lengths of the hard and soft segments were calculated from molecular weights and copolymer compositions. © 1994 John Wiley & Sons, Inc.