bluuebunny/crossref_metadata_2025 huggingface dataset:
Light scattering from swollen textured polymer network composites
Authors: Patlazhan S. A.
Published: April 2003

Light scattering from a swollen textured heterogeneous polymer network is discussed using example of a network composite filled by spherical inclusions anisotropically distributed in the matrix. The dependence of the scattering intensity on the Fourier transform of the correlation function dry‐state shear moduli fluctuations has been established. Hv scattering patterns from uniaxial textures and their ratio with the composite anisotropy parameter are analyzed. The sensitivity of the Hv scattering pattern on restrictions during the swelling is emphasized. © 1993 John Wiley & Sons, Inc.
Study of structure and polymerization of epitaxially grown SiPc(OH)2 thin films by high‐resolution electron microscopy
Authors: Kawase Noboru , Kurata Hiroki , Kubono Koji , Isoda Seiji , Kobayashi Takashi
Published: April 2003

Thin films of SiPc(OH)2 (Pc = phthalocyanine) were formed epitaxially on the (001) surface of mica by vacuum deposition and were then polymerized by heat treatment. The molecular packing of the SiPc(OH)2 was determined by electron diffraction and high‐resolution electron microscopy as triclinic\documentclass{article}\pagestyle{empty}\begin{document}${\rm P\bar 1} $\end{document} having dimensions a = 0.727, b = 1.307, c = 0.688 nm, α = 102.5, β = 104.2, and γ = 97.4°. This monomer crystal grows with its c‐axis parallel to the a‐axis of the substrate mica and its bc‐plane parallel to the (001) surface of mica. By heat treatment at 320°C, the SiPc(OH)2 polymerized with the c‐axis of the polymer parallel to the c‐axis of the monomer. At 420°C, the c‐axis of the polymer became parallel to the a*‐axis of the monomer (i.e., perpendicular to the film surface). From high‐resolution electron microscopy of partially polymerized specimens, the polymerization was shown to start at the edges of small monomer crystals. This may be considered to be due to the volume expansion during the polymerization. © 1993 John Wiley & Sons, Inc.
On the flexibility of cyclochain polymers
Authors: Pavlova S. S. A. , Ronova I. A. , Timofeeva G. I. , Dubrovina L. V.
Published: April 2003

Conformational parameters for a wide variety of aromatic cyclochain polymers have been computed assuming free rotation about virtual bonds. The flexibility with free rotation is shown to be determined by the geometry of the repeat unit and can vary over a wide range (15–1500 Å). Experimental values of the Kuhn segment length A are calculated from literature data on the hydrodynamic behavior of polymeric macromolecules of this class in solution. For most polymers Afr for free rotation is equal to the experimental Aexp, and hindered rotation is mainly due to bulky substituents. © 1993 John Wiley & Sons, Inc.
The microstructure and macrostructure of sulfonated poly(ethylene terethphalate) fibers
Authors: Timm Debra A. , Hsieh You‐Lo
Published: April 2003

The effects of fiber‐forming processes on the microstructure and macrostructure and overall orientation in sulfonated poly(ethylene terephthalate) (SPET) fibers are reported. The processing parameters examined include drawing, crimping, relaxing, and annealing. Drawing and annealing cause changes in both the crystalline structure and molecular packing in the noncrystalline regions, while crimping and relaxing appear to affect only the noncrystalline regions. A bimodal melting endotherm was observed for the SPET fibers. Experimental data suggest the low‐temperature endotherm of the SPET fibers originates from melting of the crystalline structure formed on drawing, and that the high‐temperature endotherm results from melting the heat‐induced crystals formed during fiber processing and/or thermal analysis. Compared to the PET fibers, the SPET chains in the undrawn fibers appear to have higher mobility, are easier to crystallize, and form smaller crystals upon drawing as well as DTA heating. At the crimped stage, the SPET fibers have higher overall molecular packing but lower overall orientation than the PET fibers. The differences in physical and thermal properties between the analogous SPET and PET fibers are related to their different responses to processing variations because of molecular weight and sidegroup effects. © 1993 John Wiley & Sons, Inc.
Ionic conductivity of conjugated water‐soluble rigid‐rod polymers
Authors: Dang T. D. , Bai S. J. , Heberer D. P. , Arnold F. E. , Spry R. J.
Published: April 2003

Poly[(1,7‐dihydrobenzo[1,2‐d:4,5‐d′] diimidazole‐2,6‐diyl)‐2‐(2‐sulfo)‐p‐phenylene], a conjugated rigid‐rod polymer, was derivatized with pendants of propane‐sulfonated ionomers. The derivatized rigid‐rod polymer was soluble in aprotic solvents as well as in water for isotropic solutions that were processed into isotropic films. Direct‐current electrical conductivity σ of the films was measured using the four‐probe technique. Room‐temperature σ as high as 2.9 × 10−4S/cm was achieved on pristine isotropic films without using dopants. When the rigid‐rod polymer concentration exceeded 25 wt %, the isotropic solution could be transformed into a liquid‐crystalline solution that allowed deformations to be applied to produce anisotropic films. Significant increase in σ was obtained in a sheared film along both the parallel direction (∥) and the transverse direction (⊥) with a σ∥/σ⊥ = 5. Additionally, enhanced σ was realized in films heat‐treated at about 100°C, in the derivatized polymer with higher molecular weight from dialysis, and in substituting the sulfonated ion Na+ by H+ in the pendants of the polymers. Constant‐voltage measurements were applied to the polymers to monitor the σ stability for ascertaining the nature of the conductivity. No electronic contribution in σ was detected. Instead, a monotonically decreasing σ was consistently observed indicative of ionic conductivity. © 1993 John Wiley & Sons, Inc.
Quantitative characterization of optical anisotropy in high refractive index films
Authors: Hardaker S. S. , Moghazy S. , Cha C. Y. , Samuels R. J.
Published: April 2003

Waveguide coupling measurements of polymers have largely concentrated on the application of mode analysis to the study of thin supported films (such as spin coatings). The use of prism coupling to study thick, freestanding polymer films, however, has not been reported. In this paper, the ability of prism coupling to characterize the three‐dimensional optical properties of thick, freestanding polymer films and sheets is demonstrated. A modified prism coupling procedure is described that allows the determination of all three principal refractive indices in thick, three‐dimensionally anisotropic freestanding films. A Metricon prism coupler is used in a manner similar to an Abbé refractometer for the measurement of isotactic polypropylene, poly(ethylene terephthalate), PMDA‐ODA polyimide, and poly(phenylene sulfide). Three series of PMDA‐ODA films are also investigated in this study. The first series has been drawn to different extensions from three‐dimensionally random films. The second series has random orientation in the plane of the film but different degrees of planarity with respect to the through direction. The third series are commercial films of varying thickness. These three series of films are compared as to the optical an‐isotropy that is developed from the three different fabrication processes. © 1993 John Wiley & Sons, Inc.
Fifty years of light scattering: A perspective
Authors: Stein Richard S. , Srinivasarao Mohan
Published: April 2003

It is 50 years since Debye first described the use of light scattering for the characterization of polymer solution. Ben Chu has been a leader in its subsequent development. Significant advances in theory, experimental techniques, their interpretation, and application during this period are described. © 1993 John Wiley & Sons, Inc.
Irreversible formation of a network during melting/dissolution of nascent PE
Authors: Delmas Geneviève
Published: April 2003

A high temperature endotherm has been reported recently for PE samples during a slow T ramp which has been associated with a phase change in strained chains. From comparison of NMR and calorimetric data on nascent and melt/recrystallized samples, the following origin of the strain is now proposed. Nascent PE is a homogeneous material which contains a sizeable proportion of short‐range ordered chains interrupted by loose knots. Due to expansion during melting, the knots become tighter and a physical network which encompasses a fraction of the chains is produced. The network so formed interrupts the melting process in the ordered chains. In PE and other polyolefins, melting resumes at higher T. The high T endotherms of physical and chemical networks are compared. The consequences of this network for polymer properties as well as its general occurrence are discussed briefly. © 1993 John Wiley & Sons, Inc.
Matched ring diblock and linear triblock copolymers in dilute solution
Authors: Amis Eric J. , Hodgson Donald F. , Wu Wenjun
Published: April 2003

A unique diblock copolymer ring and its linear triblock copolymer precursor composed of polystyrene and polydimethylsiloxane have been characterized by static and dynamic light scattering in dilute solution. The measurements were carried out with cyclohexane as the solvent over a temperature range of 12–35°C. Cyclohexane has the useful property that it is nearly isorefractive with the PDMS so that the PDMS block segments are invisible to the light‐scattering technique and it is a theta solvent for polystyrene at 34.5°C. The block polymers in this work contain 35.1 wt % of styrene as determined by proton NMR. In the linear triblock polymer, the polystyrene is the center block with PDMS blocks on each side. Static light scattering measurements give 4.31 × 104 for the average molecular weight of the whole polymer. Light scattering also shows that the apparent theta temperature for the linear triblock is shifted by 15°C to a value of 20°C at which point the second virial coefficient drops sharply and phase separation begins to induce aggregation. The diblock ring, however, shows a strongly positive second virial coefficient and no aggregation even at 12°C which is the limit of these experiments. The diffusion coefficients of cyclic diblock (Dc) and linear triblock copolymer (D1) are measured by dynamic light scattering. The ratio of diffusion coefficients of cyclic and linear copolymers at 14.9°C and 30°C are Dc/Dl = 1.13 and 1.107 respectively. These compare well with prediction of 1.18 for this ratio from consideration of the hydrodynamics of matched linear and cyclic polymer chains. Dynamic light scattering quantitatively confirms that the linear copolymer experiences a solvent quality change near 20°C but the cyclic polymer remains in good solvent over the entire experimental temperature range. © 1993 John Wiley & Sons, Inc.
Sorption and partial molar volumes of gases in poly(ethylene‐co‐vinyl acetate)
Authors: Kamiya Yoshinori , Naito Yasutoshi , Bourbon Dominique
Published: April 2003

Sorption and dilation properties of polymer‐gas systems involving poly(ethylene‐co‐vinyl acetate) and N2, CH4, or CO2, have been investigated at pressures up to 50 atm at temperatures of 10–40°C. Sorption isotherms for low‐solubility gases (i.e., CH4 and N2) can be described by Henry's law, and those for high‐solubility gas (i.e., CO2) by Flory‐Huggins dissolution equation. Dilation isotherms are similar in contour to the corresponding sorption isotherms. From the obtained sorption and dilation data, partial molar volumes of the gases in the polymer were determined as a function of temperature. Thermal expansivity of dissolved CO2 molecules was estimated at ca. 2.4 × 10−3°C−1 from the temperature dependence of partial molar volume. The expansivity is smaller than that of liquid CO2 and larger than those of the polymer and organic liquids. © 1994 John Wiley & Sons, Inc.
Effect of network heterogeneity on tensile and tear strengths of radiation, peroxide, efficient and conventional cured polyisoprene
Authors: Grobler J. H. A. , McGill W. J.
Published: April 2003

At any given crosslink density, the ultimate tensile and tear strengths of vulcanizates depend on the curing system and decrease in the order: conventional (CV) > efficient (EV) > peroxide > radiation cured. Measurements on three network parameters were interpreted as indicating that crosslinks were not uniformly distributed throughout the networks and that network heterogeneity decreased in parallel with a decrease in physical properties. (1) Plots of the freezing point of the gel‐solvent in a network, swollen to equilibrium, versus the volume fraction of rubber in the swollen gel, showed a straight line relationship for radiation cured networks and an increasingly large deviation from linearity on passing from radiation cured networks through peroxide and EV to CV cured networks. (2) The glass transition temperature of CV cured networks was higher than that of radiation cured networks of the same crosslink density. (3) Scanning electron micrographs of cryofracture surfaces showed a more uneven surface in CV than in radiation cured networks. The development of heterogeneity in the four networks studied is discussed in terms of the reactions that lead to crosslinking with the different curing systems. © 1994 John Wiley & Sons, Inc.
Novel rolltruded films. II. Effect of draw ratio on the gas transport properties of rolltruded isotactic poly (propylene)
Authors: Ciora R. J. , Magill J. H.
Published: April 2003

Modification of the gas transport properties of rolltruded isotactic poly(propylene) films have been studied. Changes in the amorphous solubility, diffusivity, and the activation energies of CO2, N2, and CH4 in iPP rolltruded at 150°C for draw ratios to ca. 20 are recorded. At this processing temperature variations in the transport coefficients have been found to be weakly dependent upon draw ratio and do not suffer the dramatic reductions often reported in uniaxially drawn polymers. In general, the morphological differences between uniaxially drawn and rolltruded films are subtle and are responsible for the significant difference in the measured transport properties. © 1994 John Wiley & Sons, Inc.
The influence of pressure‐induced structural changes on the ionic conductivity of zwitterionic polymers
Authors: Cardoso J. , Montiel R. , González L. , Huanosta A. , Manero O.
Published: April 2003

In this investigation, ionic conductivity measurements are performed on N‐oxide polymers neutralized with NaOH. The polymer samples were conformed in disk shapes using an Instron machine considering various values of the pressure required to compact the samples. The dielectric properties of these systems were obtained by the a.c. spectroscopy technique. Results indicate a substantial variation in the ionic conductivity due to the pressure‐induced structural changes on the morphology of these samples, as confirmed by WAXS studies. © 1994 John Wiley & Sons, Inc.
Complexation of poly(ethylene oxide) and urea
Authors: Bogdanov Bogdan G. , Michailov Marin , Uzov Christo V. , Gavrailova Girka G.
Published: April 2003

The complexation of ultrahigh‐molecular‐weight poly(ethylene oxide) (PEO) with urea in both the solid and molten states was studied by infrared spectroscopy. Information about the temperature dependences of the absorption bands in the 3600–2600 and 1300–600 cm−1 region on heating and cooling was obtained. Some conclusions concerning the interaction between PEO and urea were also made. The formation of a high temperature, metastable molecular complex between PEO and urea, which is susceptible to undercooling, was confirmed spectroscopically. Heating to 85–90°C resulted in a molecular complex stable at room temperature.© 1994 John Wiley & Sons, Inc.
Environment‐induced morphological changes of polyethylene lamellae during crystallization in solution
Authors: Kawaguchi Akiyoshi , Ohara Masayoshi , Tsuji Masaki
Published: April 2003

Polyethylene (PE) lamellar crystals were grown by two dual‐staged crystallization methods: (1) Fractionated PE was first crystallized from n‐octane by the self‐seeding method, the solvent of the resulting suspension of crystals was exchanged for p‐xylene, and thereafter, the suspension was mixed with a solution in p‐xylene at various temperatures so that PE grew from p‐xylene onto the lamellae pregrown from n‐octane, and (2) according to the similar procedure, PE lamellae were first grown from p‐xylene and subsequently, PE was deposited from n‐octane onto the lamellae pre‐grown from p‐xylene. In the crystallization procedure (1), triangular lamellae with the 〈010〉 chain folding developed randomly on the {100} lateral surfaces of truncated parent lamellae so that the surfaces were serrated, and otherwise, thin daughter lamellae bordered the parent lamellae along the {110} surfaces, retaining the flat growth fronts with the 〈110〉 folding. In the procedure (2), the {100} sectors with the 〈010〉 folding developed at the apexes of the long diagonal of lozengeshaped parent lamellae, and consequently, their morphology was transfigured into a truncated crystal. These morphological transformations are discussed on the basis of the change in the interfacial free energy between the parent crystal and the surrounding phase due to the substitution of solvent. © 1994 John Wiley & Sons, Inc.
In situ measurement of the glass transition temperature of polymers with compressed fluid diluents
Authors: Condo P. D. , Johnston K. P.
Published: April 2003

In situ measurement of the creep compliance of poly(methyl methacrylate) (PMMA) and poly(ethyl methacrylate) (PEMA), equilibrated with a pressurized CO2 phase, is used to determine the glass transition temperature. Corrections due to dilation of the polymer by CO2 as well as the buoyancy are assessed. Both polymer systems exhibit a recently discovered phenomenon, retrograde vitrification, in which a liquid polymer becomes a glass with an increase in temperature. The experimental results are predicted semi‐quantitatively in terms of the temperature and pressure effects on the solubility of the compressed fluid in the polymer. © 1994 John Wiley & Sons, Inc.
Morphologies and electro‐optic properties of polystyrene/liquid crystal composite films
Authors: Kim Byung Kyu , Ok Young Sook
Published: April 2003

Morphology and electro‐optic properties of composite films composed of polystyrene (PS) and nematic liquid crystal (LC) have been studied for a wide range (30‐70 wt% of liquid crystal) of film composition. At two specific levels of LC loadings (50 and 60 wt%), effects of temperature, frequency and voltage of applied ac electric field on the transmittance of the films were intensively measured, and the results were interpreted in terms of aggregation structure of the film, the geometry of LC domains, LC loading, dielectric constant, conductivity, birefringence, and the solubility of LC in polymer. © 1994 John Wiley & Sons, Inc.
The mechanical anisotropy of stratified polyvinyl chloride
Authors: Sinan Özkan H. , Oskay Taner , Yüksel Güney H. , Dirim Hüseyin
Published: April 2003

The mechanical anisotropy of a material obtained by stratification of oriented polyvinyl chloride (PVC) layers in different ways has been studied. PVC layers, uniaxially oriented by drawing each with a different draw ratio, were stratified in such a way that their draw axes were either parallel or perpendicular. The propagation velocities of ultrasonic pulses were measured in three principal planes defined by draw axes of the stratified material. With an immersion technique, measurements were performed at 2 MHz and 22°C. Experimentally, it was shown that while stratification of layers with draw axes parallel preserves hexagonal symmetry, the stratified material with layers' draw axes perpendicular possesses orthorhombic symmetry. © 1994 John Wiley & Sons, Inc.
Dynamic mechanical properties of epoxy resin/epoxidized rubber blends: Effect of phase separated rubber
Authors: Bussi Philippe , Ishida Hatsuo
Published: April 2003

The dynamic mechanical properties of blends of diglycidyl ether of bisphenol‐A‐based epoxy resin and internally epoxidized polybutadiene rubber have been studied. It is shown that the influence of the composition of the continuous phase and of the dispersed phase can be studied not only from the variations of the glass transition temperature but also from the changes in the apparent enthalpy of activation associated with this transition. As the initial rubber content increases, the composition of the dispersed phase remains practically constant while more rubber is able to dissolve in the continuous phase. Analysis of the rubbery plateau region reveals that the shear modulus of the blends is not much affected by the presence of dissolved rubber in the continuous phase but strongly depends on the volume fraction of dispersed phase. This volume fraction can be obtained from the relative drop in shear modulus after modeling the results with the Kerner equation. The results compares well with independent measurements by scanning electron microscopy. © 1994 John Wiley & Sons, Inc.
Molecular orientation and microstructure of roller‐drawn sheets of poly(ether ether ketone)
Authors: Kaito A. , Nakayama K.
Published: April 2003

The rolling and roller‐drawing of poly(ether ether ketone) (PEEK) sheets were carried out in the roller temperature range of 165‐262°C. The crystal orientation functions of the PEEK sheets were determined from the azimuthal intensity distribution of wide‐angle x‐ray diffraction, and the orientation behavior in the amorphous region was characterized by the measurements of sonic modulus and polarized fluorescence. The orientation functions increase monotonically with increasing draw ratio. The orientation function in the amorphous region is close to that of crystal orientation function of the same sample. The long period evaluated by small‐angle x‐ray scattering is almost constant over the draw ratio range studied, whereas the crystallite size along the 001 plane, D001 tends to increase with increasing draw ratio. The value of the crystallite size exceeds the product of the crystallinity and the long period. The result suggests the formation of the crystalline linkages that penetrate the periodic layers. © 1994 John Wiley & Sons, Inc.
The influence of alkylene spacers on conformational and thermal properties of poly (aryl methacrylates)
Authors: Chen Yuan‐Ju , Mays Jimmy W. , Hadjichristidis Nikos
Published: April 2003

The effect of introducing alkylene spacers on the thermal and conformational properties of poly(aryl methacrylates) has been studied. Poly(2‐phenylethyl‐1‐methacrylate) (PPEMA) and poly(4‐phenylbutyl‐1‐methacrylate) (PPBMA) samples of narrow poly‐dispersities and covering a very broad range of molecular weights were produced by free radical solution polymerization, followed by fractionation. These materials were studied by a combination of differential scanning calorimetry, light scattering, and viscometry measurements to allow evaluation of their glass transition temperatures (Tg) and characteristic ratios (C∞). These results are compared with literature data available for poly(phenyl methacrylate) (PPMA), which has no alkylene spacer, and poly(benzylmethacrylate) (PBMA), which has a methylene spacer. A progressive decrease in Tg is observed as the length of the alkylene spacer is increased, reflecting the enhancement of side group (local) flexibility. C∞ decreases substantially on going from PPMA to PBMA but then increases on going to PPEMA and PPBMA. This behavior is attributed to the fact that while side group flexibility increases for the materials with longer alkylene spacers, and this would be expected to decrease C∞, the side group size is progressively increasing. Larger side groups generally increase C∞ of polymethacrylates. Thus the observed C∞ behavior for these polymers reflects both the size and flexibility of the substituents. © 1994 John Wiley & Sons, Inc.
Dynamic relaxation behavior of solvent‐crystallized poly(ether ether ketone)
Authors: Kalika D. S. , Nickell J. C. , Krishnaswamy R. K. , Barton B. F.
Published: April 2003

The dynamic relaxation behavior of solvent‐crystallized poly(ether ether ketone) (PEEK) has been investigated in the region of the glass‐rubber (α) relaxation using dynamic mechanical and dielectric methods. Amorphous PEEK films were exposed to saturated methylene chloride and acetone vapor, with solvent‐induced crystallization observed for both penetrants. Sample desorption at elevated temperatures (under vacuum) resulted in virtually complete removal of residual penetrant, thus providing for the measurement of relaxation characteristics independent of plasticization. Both dynamic mechanical and dielectric studies indicated a marked positive offset in the isochronal relaxation temperatures of the solvent‐crystallized samples relative to thermally crystallized specimens of comparable bulk crystallinity, and a higher apparent activation energy in the solvent‐crystallized case. These results are consistent with the evolution of a tighter crystalline morphology (i.e., smaller crystal long spacing) in the solvent‐crystallized samples, the crystallites imposing a greater degree of constraint on the long‐range motions of the amorphous chains inherent to the glass‐rubber relaxation. © 1994 John Wiley & Sons, Inc.
Temperature measurements of the gaseous emission during the fracture of polystyrene: A determination of the fracture energy and fracture surface temperature
Authors: Dickinson J. T. , Jensen L. C. , Langford S. C. , Dion R. P.
Published: April 2003

The emission of volatile species accompanying the fracture of polystyrene has been monitored as a function of time by two quadrupole mass spectrometers mounted at different distances from the sample. The resulting time‐of‐arrival signals were numerically modeled to yield an estimate of the energy per unit area dissipated as heat by fracture. Neutral emissions of ethyl benzene molecules (a common volatile impurity) and a noble gas (Arintroduced by exposure) were monitored. Dissipation (fracture) energies determined ranged from 680 to 1480 J/cm2, consistent with the range of energy release rates in the literature. The peak surface temperatures calculated from the measured heat dissipation ranged from 600 to 1300 K. © 1994 John Wiley & Sons, Inc.
Effect of glass fiber‐matrix polymer interaction on fatigue characteristics of short glass fiber‐reinforced poly(butylene terephthalate) based on dynamic viscoelastic measurement during the fatigue process
Authors: Takahara Atsushi , Magome Tateshi , Kajiyama Tisato
Published: April 2003

Fatigue behaviors of glass fiber‐reinforced poly(butylene terephthalate) (PBT) were studied based on dynamic viscoelastic measurements during the fatigue process. The fatigue strength of glass fiber‐reinforced PBT was greatly improved by strengthening the interfacial adhesion between glass fiber and matrix PBT. The heat generation rate under cyclic fatigue for PBT reinforced with surface‐unmodified short glass fiber was always larger than that reinforced with surface‐modified short glass fiber because of the large net imposed strain amplitude of PBT matrix which occurred due to the interfacial debonding under cyclic fatigue. A fatigue fracture criterion based on the magnitude of hysteresis energy loss being consumed for a structural change was established for the PBT/short glass fiber composites in consideration of glass fiber‐matrix polymer interfacial interaction. © 1994 John Wiley & Sons, Inc.
Sub‐Tg molecular motions in glassy poly(vinyl chloride). Influence of the nucleophilic substitution
Authors: Del Val J. J. , Colmenero J. , Martínez G. , Millán J. L.
Published: April 2003

Dielectric local molecular motions in the glass transition region of poly(vinyl chloride) (PVC) have been investigated by means of the isothermal depolarization currents technique. Attention is paid to the influence of the modification of the polymer by the substitution of chlorine atoms of PVC chain by the benzenethiolate group. The results are well described by stretched exponential laws. According to the Ngai's coupling model, the coupling between moving units as well as the activation energy responsible for the motions occurring at primitive level have been calculated for each sample at each temperature. All these parameters are noticeably altered by the modification of PVC. © 1994 John Wiley & Sons, Inc.
Phenolic materials via ring‐opening polymerization of benzoxazines: Effect of molecular structure on mechanical and dynamic mechanical properties
Authors: Ning Xin , Ishida Hatsuo
Published: April 2003

A series of benzoxazine compounds have been prepared from different bifunctional phenols and primary amines and the molecular compositions of the precursors are characterized by nuclear magnetic resonance, Fourier transform infrared, and size exclusion chromatography. It has been demonstrated that by design of the molecular structures of the benzoxazine precursors, therefore by tailoring of the network molecular architectures, new phenolic materials with superior mechanical and thermal properties, and ease‐of‐processing characteristics can be obtained. The characteristics of dynamic mechanical spectra of the phenolic materials are studied and related to their structural features. © 1994 John Wiley & Sons, Inc.
Structural changes of silk fibroin membranes induced by immersion in methanol aqueous solutions
Authors: Tsukada Masuhiro , Gotoh Yoko , Nagura Masanobu , Minoura Norihiko , Kasai Nobutami , Freddi Giuliano
Published: April 2003

Structural changes of native and regenerated silk fibroin membranes were induced by immersion in water‐methanol solutions and examined as a function of immersion time and methanol concentration. X‐ray diffractometry and infrared spectroscopy data showed that transition from random coil to β‐sheet structure occurred favorably when both native and regenerated silk fibroin membranes were immersed in water‐methanol solutions, regardless of the different immersion time. Only native silk membrane, treated for 2 min with pure methanol, maintained its original amorphous structure, as demonstrated by differential scanning calorimetric (DSC) curves. The degree of displacement, measured by thermomechanical analysis (TMA), was much greater for regenerated than for native silk fibroin membranes. SDS‐PAGE pattern showed that native silk fibroin has a molecular weight of 350, while the regenerated sample is formed by a large number of polypeptides in the range of 200‐50 KD. The amount of acidic and basic amino acids decreased slightly in regenerated silk fibroin. Physical properties of silk membranes treated with water‐methanol solutions are discussed in terms of membrane structure, treatment conditions, and chemical structure of starting material. © 1994 John Wiley & Sons, Inc.
Cyclic polymers swollen in a good solvent dynamic scattering properties
Authors: Benmouna M. , Borsali R. , Rinaudo M.
Published: April 2003

A general formalism for the dynamic scattering properties of cyclic polymers in good solvent conditions is presented. Single‐chain dynamics are investigated in the framework of the Oseen tensor model with and without the preaveraging approximation. The chain swelling due to excluded volume interactions is introduced by a renormalization of the internal chain statistics of cyclic polymers. The relaxations of the concentration fluctuations are also described for both ring homopolymers and copolymers. © 1994 John Wiley & Sons, Inc.
Emission of occluded volatiles during deformation of polycarbonate due to strain‐enhanced diffusion
Authors: Dickinson J. T. , Jensen L. C. , Langford S. C. , Dion R. P.
Published: April 2003

Measurements of the emission of purposely entrained volatiles (Ar and D2O) during the loading and unloading of a bisphenol‐A polycarbonate in vacuum are made by quadrupole mass spectrometry. Transient loading events are accompanied by dramatic increases in emission, reflecting a similar rise in the diffusion constant of the measured species. We attribute this change to an increase in size of molecular voids in the polymer network, which accompany the increase in sample volume under load. The results are interpreted in terms of the Dolittle relation in which the diffusion constant depends exponentially upon v*/vf0, the ratio between an activation volume for diffusion and the average size of the relevant voids in the polymer network. Our data suggests that v*/vf0 is unusually low in the D2O‐polycarbonate system, which we attribute to a relatively large value of vf0; this would be consistent with the relatively long distance between flexible links in the polycarbonate structure. © 1994 John Wiley & Sons, Inc.
Depolarization thermocurrent studies in poly(hydroxyethyl acrylate)/water hydrogels
Authors: Kyritsis A. , Pissis P. , Ribelles J. L. Gómez , Pradas M. Monleón
Published: April 2003

Detailed investigations on the dielectric relaxation mechanisms in poly(hydroxyethyl acrylate) (PHEA), by means of the thermally stimulated depolarization currents (TSDC) method in the temperature range 77‐300 K are reported. There is particular interest in the dependence of the dielectric relaxation mechanisms on the water content h, h = 0 − 0.5 w/w, in an attempt to contribute to a better understanding of the physical structure of water in the PHEA hydrogels. We employ thermal sampling (TS) and partial heating (PH) techniques to experimentally analyze the observed complex relaxation processes, due to the secondary (βsw) and the main (α) relaxation, into approximately single responses and to determine the spectra of activation energies E(T) at different h values. Measurements with different electrode configurations reveal different aspects of the dynamics of the relaxation mechanisms and allow the distinction between dipolar and conductivity relaxation contributions. It is shown that by means of these techniques we can determine certain temperature characteristics for the α relaxation and investigate their dependence on water content. We discuss the relation of these characteristic temperatures to the calorimetric glass transition temperature Tg. © 1994 John Wiley & Sons, Inc.
Swelling studies of crosslinked poly(p‐phenylene terephthalamide) copolymers in sulfuric acid
Authors: Rigney Jennifer , Little Monica D. , Martin David C.
Published: April 2003

In an attempt to improve the mechanical properties of extended chain polymers such as poly(p‐phenylene terephthalamide) (PPTA), a crosslinkable terephthalic acid derivative (XTA) has been developed which can be incorporated into copolymers in various concentrations and activated after polymerization. The crosslinking of PPTA‐co‐XTA copolymer particles was investigated through a series of swelling experiments in concentrated H2SO4. The data show a systematic decrease in equilibrium swelling with increasing XTA content, indicating the XTA units are in fact acting as crosslink sites. Values for crosslink density were calculated from the Flory‐Rehner theory of polymer swelling and compared with previous findings on crosslinked rigid polymer network systems. The effective number of crosslinks per XTA unit (efficiency) predicted by the Flory‐Rehner theory increases and then decreases with % XTA. The decrease in crosslinking efficiency at high XTA concentrations is consistent with differential scanning calorimetry data which show the enthalpy of XTA reaction decreasing slightly with % XTA. The deviations at low % XTA may represent a failure of the Flory‐Rehner theory to properly describe the rubbery elasticity of extended chain polymers. © 1994 John Wiley & Sons, Inc.
Characteristics of charged networks under an electric stimulus
Authors: Kwon Ick Chan , Bae You Han , Kim Sung Wan
Published: April 2003

The electrokinetic phenomena of poly(2‐acrylamido‐2‐methyl‐1‐propane sulfonic acid‐co‐n‐butylmethacrylate) were examined to investigate physical changes of the gel under an applied electric current. When an electrical stimulus was applied to a piece of the gel, without being in contact with an electrode, reversible gel bending was observed. The bending degree was directly proportional to the intensity of the applied electric stimulus. This was explained by ‘depletion polarization’ of ionic species under the stimulus. The swelling of the gel surface facing the anode increased, due to the decreased ionic strength of the boundary layer upon electric stimulation, while gel shrinking occurred at the cathode. When the gel is in direct contact with electrodes, deswelling of the gel was observed at the anode side, while water seepage occurred at the cathode side. This observation was attributed to the electro‐osmosis inside the gel, combined with local pH changes around the electrodes resulting from electrochemical reactions, particularly water electrolysis. © 1994 John Wiley & Sons, Inc.
Modelling of water transport in ionic hydrophilic polymers
Authors: Hariharan Deepak , Peppas Nikolaos A.
Published: April 2003

Water and ion transport in thin sheets of initially dry, ionic, hydrophilic crosslinked polymers was modelled throughout the dynamic swelling process. The water transport was expressed in terms of a non‐Fickian equation with a diffusion term containing a Fujitatype concentration‐dependent diffusion coefficient coupled with a pseudoconvective term arising from the reasonable assumption that the stress in ionic polymers is proportional to the total number of ionized pendant groups in the polymer. Ion transport was expressed in terms of generalized Fickian equations with water concentration‐dependent diffusion coefficients. These equations were solved with appropriate boundary conditions to establish the water uptake as a function of time, pH and ionic strength in a citrate‐phosphate‐borate buffer solution. A new dimensionless number, the Stress Swelling number, A, was defined to quantify the relative importance of stress in the overall swelling process. Water uptake was a strong function of A. © 1994 John Wiley & Sons, Inc.
Block copolyetheramides III. Blends of nylon‐6 and block copolyetheramides
Authors: Chung Lie‐Zen , Kuo Dee‐Lun , Tsai Hong‐Bing
Published: April 2003

Blends of Nylon‐6 and block copolyetheramides with hard segments of Nylon‐6 and soft segments of poly(tetramethylene ether) were prepared. The impact strength of the blends was enhanced by the presence of the block copolyetheramides as compared to the Nylon‐6. Different block copolyetheramides exhibited different effects on the impact strength which could be described as the difference in compatibility between the Nylon‐6 and the Nylon‐6 segments of the block copolymers. The difference in compatibility was verified by the investigations of TEM and DSC. As the caprolactam content of the block copolyetheramides increased, the compatibility between the Nylon‐6 and the Nylon‐6 segments of the block copolymers was enhanced and the blends exhibited a higher impact strength in general. The heat deflection temperature of the blends decreased as the polyether content (depending on the type and the content of the block copolyetheramide) of the blends increased. When the polyether content was ≤ or 20 wt %, a small decrease in heat distortion temperature was found. © 1994 John Wiley & Sons, Inc.
Protonation of CIS‐PBO in metanesulfonic acid solutions
Authors: Roitman Daniel B. , McAlister Jan , McAdon Marc , Wessling Ritchie A.
Published: April 2003

A comparative study of the conductivity behavior of methane‐sulfonic acid solutions of poly(p‐phenylene‐cis‐benzobisoxazole) or cis‐PBO and other compounds, including CH3SO3Na (NaMSA), a cis‐PBO model compound, and 6,7‐dimethyl‐2,3‐di(2‐pyridyl) quinoxaline, a molecule containing four protonating sites, was carried out to determine the degree of protonation of PBO and its model compound. The conductivity dependence with increasing cis‐PBO concentration indicates that only two sites per repeat unit are protonated. © 1994 John Wiley & Sons, Inc.
Raman spectral study of solid and dissolved poly(vinyl alcohol) and ethylene‐vinyl alcohol copolymer
Authors: Cooney T. F. , Wang L. , Sharma S. K. , Gauldie R. W. , Montana A. J.
Published: April 2003

We have measured the Raman spectra of ethylene‐vinyl alcohol copolymer (EVOH) and poly(vinyl alcohol) (PVOH). Spectra of 88% hydrolyzed PVOH were examined from the partially crystalline solid, from PVOH dissolved in both H2O and D2O, and from films precipitated from these solutions. The spectrum in H2O differs from that of the starting material by disappearance of sharp bands having Raman shift values of 1146 and 1093 cm−1, strengthening of a band near 915 cm−1, decrease in frequency of bands at 480, 1356, and 1441 cm−1, and increase in frequency of bands at 369, 413, 1023, 1371, and 2910 cm−1. The spectrum of the film shows partial reversal of these trends. With D2O as the solvent, the band shifts are slightly different from those listed above and new bands appear. These changes are indicative of loss of crystallinity, change in stereochemistry, and partial deuteration of hydroxyl during dissolution of this PVOH sample at room temperature. © 1994 John Wiley & Sons, Inc.
Ethanol‐induced crack healing in poly(methyl methacrylate)
Authors: Wang Peng‐Peng , Lee Sanboh , Harmon Julie P.
Published: April 2003

The crack healing induced by ethanol in poly(methyl methacrylate) (PMMA) has been studied at temperatures of 40–60°C. Crack healing occurs because the effective glass transition temperature of PMMA is reduced to below the test temperature by ethanol plasticization. It is found that crack closure rate is constant at a given temperature. The fracture strength of healed PMMA is lower than that of the original samples. By comparing the fracture stress with the morphology of the crack edge on the PMMA surface, we found that a high degree of swelling is responsible for the incomplete recovery of mechanical strength. The fractography of the completely healed sample shows a very different fracture morphology from that of virgin PMMA. The transport of ethanol in PMMA also is studied. At lower temperatures, transport is described by ideal Case II behavior. As the temperature increases, the kinetics shift from ideal Case II to anomalous behavior. The first stage of crack healing is controlled by Case I transport. © 1994 John Wiley & Sons, Inc.
Hydrogen bonds in regioselectively substituted cellulose derivatives
Authors: Kondo Tetsuo
Published: April 2003

Formation of hydrogen bonds in various cellulose derivatives, 2,3‐di‐O‐ and 6‐O‐substituted cellulose ethers, were characterized by FTIR and solid‐state CP/MAS13C‐NMR. The polymers were synthesized by regioselective substitution of hydroxyl groups and had a uniform structure. Since their three hydroxyl groups (OH) are selectively blocked, the cellulose derivatives appeared to form specific inter‐ and intramolecular hydrogen bonds. The characteristic OH stretching frequencies in IR spectra and the C‐1 chemical shift in CP/MAS spectra of 6‐O‐substituted cellulose derivatives indicated existence of two equivalent intramolecular hydrogen bonds between ether oxygen and OH groups at 3‐OH‐O5′ and O6‐HO‐2′ [Figure 3(C)]. Influence of the substituents at the C‐6 position on the formation was not significant except trityl group. Behavior of the hydrogen bonds in 6‐O‐tritylcellulose were also discussed. © 1994 John Wiley & Sons, Inc.
A new class of aromatic poly‐ether‐aroyl‐oxadiazoles. II. Studies on the cyclization reaction, infrared, structural, and morphological characterization
Authors: Calandrelli L. , Di Pace E. , Laurienzo P. , Malinconico M. , Martuscelli E. , Volpe M. G.
Published: April 2003

Poly‐ether‐aroyl‐oxadiazoles (PEODZ) of general formula: chemical structure image are reported.

Thermal cyclization of the starting polyhydrazides, infrared, thermal, and structural characterization are discussed as function of the number of methylene spacers in the range 2–12.

It is found that the position of melting is strongly dependent upon the number ofCH2, and that moldable polyoxadiazoles are obtained at × values > 7. The spherulitic nature of PEODZ is clearly revealed by thermal‐optical microscopy which, together with isothermal crystallizations at the differential scanning calorimeter, gives a close insight into the crystalline organization of such polymers. © 1994 John Wiley & Sons, Inc.
FTIR analysis of hydrogen bonding in amorphous linear aromatic polyurethanes. I. Influence of temperature
Authors: Wang Fu Cai , Feve Michel , Lam Thanh My , Pascault Jean‐Pierre
Published: April 2003

Fourier‐transform infrared spectral studies of an amorphous linear aromatic polyurethane at various temperatures were performed. Hydrogen bonding was studied in the NH stretching (3347 cm−1) and the bending (1535 cm−1) regions, using the band decomposition technique. The variations with temperature are used to calculate the ratio of the absorptivity coefficients for the H‐bonded to the “free” NH vibrations. This ratio is found to be independent of temperature. The enthalpy and the entropy of hydrogen bond dissociation are also obtained as 9.6 kJ mol−1 and 44.8 J mol−1 K−1, respectively. Two CC in‐plane vibrational bands of the aromatic rings at 1614 and 1598 cm−1 were studied at different temperatures. The integrated absorbance for both bands decreases clearly and regularly with increasing temperature, and both bands shift to lower wavenumbers. This strongly suggests a specific interaction for the aromatic rings, probably NH … π hydrogen bonds, which will be discussed in detail in the second part of this series. © 1994 John Wiley & Sons, Inc.
The influence of short‐chain branching on the creep behavior of oriented polyethylene, and its effect on the efficiency of crosslinking by electron irradiation
Authors: Rasburn J. , Klein P. G. , Ward I. M.
Published: April 2003

Studies have been made of the creep behavior of oriented (15:1) polyethylenes containing 0.4 and 1.3 butyl branches per 1000 C atoms. Increasing the branch concentration reduces significantly the creep strain and the equilibrium strain rate. The data have been fitted to an established model comprising two thermally activated processes in parallel, relating to the amorphous network at low stress, and the crystal phase at high stress. Analysis based on this model indicates the similarity between branching, entanglements, and crosslinks on the creep response. The creep behavior of electron‐beam‐irradiated materials shows that increasing the branch concentration makes the polyethylene more susceptible to mainchain scission, indicated by increased creep flow rates at higher stress, consistent with previous rubber elasticity studies. Irradiation in an acetylene atmosphere with low (< 1 Mrad) doses is shown to reduce the creep rates at all accessible stresses, and this attributed to an increase in crosslinking compared with scission. © 1994 John Wiley & Sons, Inc.
Syneresis and crystallinity in plasticized rubbery networks and composites
Authors: Pacanovsky J. , Kelley F. N. , Von Meerwall E.
Published: April 2003

We prepared polycaprolactone networks plasticized (60 wt%) with triacetin, with and without filler particles to model high‐energy solid rocket propellants. Under strain and at lower temperatures these materials partially crystallize but also undesirably exude plasticizer (syneresis). We measured both properties isothermally (30°C) on the basis of molecular mobility: crystallinity with rapid‐passage cw proton nuclear magnetic resonance (NMR), and syneresis with pulsed‐gradient spin‐echo NMR diffusion techniques, as a function of strain and time. In the gumstocks crystallinity and syneresis increase monotonically with strain and asymptotically with time. In a given specimen syneresis lags behind crystallinity but they approach the same value, suggesting that syneresis originates in expulsion of plasticizer from crystallizing regions. In the composites, crystallinity results resemble those in gum, but our diffusion data suggest that most syneresis is internal, with plasticizer accumulating in strain‐debonded void regions near filler particles. © 1994 John Wiley & Sons, Inc.