bluuebunny/crossref_metadata_2025 huggingface dataset:
Molecular weight‐dependence of free volume in polystyrene studied by positron annihilation measurements
Authors: Yu Z. , Yahsi U. , McGervey J. D. , Jamieson A. M. , Simha R.
Published: April 2003

Positron annihilation lifetime measurements are reported for four monodisperse polystyrenes with molar mass M = 4,000, 9,200, 25,000, and 400,000. The temperature dependences of orthopositronium (o‐Ps) lifetime (τ3) and intensity (I3) were measured from 5°C to Tg + 30°C for each sample. From these data, the free volume hole size, 〈vf(τ3)〉, and fractional free volume hps=CI3〈vf(τ3)〉 were calculated. The temperature dependences of τ3, 〈vf(τ3)〉 and hps show a discrete change in slope at an effective glass transition temperature, Tg,ps, which is measurably below the conventional bulk Tg. This suggests that τ3 is sensitive to large holes which retain their liquid‐like mobility in the glassy state. Good agreement was found for T > hg,ps between hps and the theoretical free volume fraction hth deduced from experimental P‐V‐T data for polystyrene using the statistical mechanical theory of Simha and Somcynsky. Below Tg,ps, deviations between hps and hth are observed, hps falling increasingly below hth as temperature decreases. Whereas hps and hth depend strongly on M in the melt, each essentially independent of M in the glass. A free volume quantity, computed from the bulk volume, which is in good numerical agreement with the Simha‐Somcynsky h‐function in the melt, gives improved agreement with hps in the glassy state. © 1994 John Wiley & Sons, Inc.
Identification and quantitative analysis of the intermediate phase in a linear high‐density polyethylene
Authors: Cheng Jinlong , Fone Matilda , Reddy Vijay N. , Schwartz Kenneth B. , Fisher Howard P. , Wunderlich Bernhard
Published: April 2003

The observation of chain conformation and mobility in polyethylene by solid‐state 13C magic angle spinning (MAS) nuclear magnetic resonance (NMR) permits unambiguous identification and quantitative analysis of an intermediate phase. The carbon‐carbon bonds in the intermediate phase adopt, on the average, an all‐trans conformation and are more mobile than in the crystalline state (room temperature rate of reorientation ≈ 107 Hz). Comparisons of crystallinities by differential scanning calorimetry, wide‐angle x‐ray diffraction, and NMR support the high orientation of the intermediate phase and suggest a lower heat of fusion than for the crystals. Results from 13C spin‐lattice relaxation and 1H spin diffusion show that the mass fractions are ≈ 20% and the domain sizes ≈ 36 Å. Both change with crystallization and annealing conditions. © 1994 John Wiley & Sons, Inc.
High field electrostrictive response of polymers
Authors: Zhenyi Ma , Scheinbeim Jerry I. , Lee Jar Wha , Newman Brian A.
Published: April 2003

It is well known that electrostrictive strains are proportional to the square of the applied electric field. It therefore appeared reasonable to assume that for some polymeric materials, a large acoustic thickness response, dT, \[
\left( {d_T = \frac{{dS}}{{dE}}} \right)
\] might be obtained by application of high dc bias fields, ∼ 20 MV/m, to a film while driving the film with an ac signal to access the high slope region of the electrostrictive strain vs. applied field curve. Previous studies of crystallizing poly(vinylidene fluoride) (PVF2) from solution under high electric fields have demonstrated that gel‐like samples of PVF2 with high content of the plasticizer tricresyl phosphate (TCP) could be subjected to electric fields as high as ∼ 100 MV/m. Using this type of heavily plasticized PVF2 dT values ∼ 4 Å/V were obtained. Values of 9 Å/V were obtained for a certain class of thermoplastic elastomer (i.e., a polyurethane). These dT values are considerably greater than those obtained from conventional piezoelectric ceramic materials. In addition, large elastic strains (> 3%) were observed as a function of applied dc field. © 1994 John Wiley & Sons, Inc.
Structure and property development in poly(p‐phenylene terephthalamide) during heat treatment under tension
Authors: Lee K.‐G. , Barton R. , Schultz J. M.
Published: April 2003

The evolution of several structural characteristics during isothermal heat treatment of poly(p‐phenylene terephthalamide) was studied. In this work, heat treatment was interrupted after different treatment times, with the specimens immediately quenched to room temperature. These specimens were then characterized by tensile testing, wide‐ and small‐angle x‐ray scattering, and optical microscopy. Structural parameters obtained from these measurements relate to crystal perfection (via the paracrystalline axial distortion parameter), axial crystallite size, transverse crystallite size, degree of chain misorientation, and degree of pleating. Structural and mechanical parameters were then plotted against heat‐treatment time to obtain kinetic isotherms for each parameter. The kinetics of the removal of chain misorientation parallels that of tensile modulus increase under all conditions. Of the other structural parameters, only the kinetics of pleat removal mimics that of modulus change, indicating that pleat removal is the effective cause of increased chain alignment and thereby of increased axial stiffness. ©1995 John Wiley & Sons, Inc.
The effect of stoichiometry on chain segment and ion mobility in partially polymerized epoxy systems
Authors: Bidstrup Sue Ann , Simpson Joycelyn O.
Published: April 2003

The temperature dependence of steady‐shear viscosity and ionic conductivity were measured for a series of unreacted mixtures and partially cured, ungelled samples of diglycidyl ether of bisphenol‐A (DGEBA) and an amine cross‐linking agent, diamino diphenyl sulfone (DDS). Six stoichiometric ratios of epoxide groups to amine hydrogens were examined. Free volume expressions were used to model the temperature dependence of the conductivity and viscosity for the unreacted DGEBA‐DDS mixtures. In addition, these expressions were combined to successfully correlate changes in viscosity and conductivity during the DGEBA‐DDS polymerization prior to gelation. It also was demonstrated that the change in weight average molecular weight during polymerization could be interpreted from the dielectric data. Through studying variations in the stoichiometry, it was possible to examine the effects of changes in chemical structure and ion concentration on the fitted parameters in the free volume models. The inherent ion transport factor (ζ0) was found to be inversely proportional to the concentration of ions in the test samples. The fractional free volume for segmental motion (B) was found to increase with an increase in the glass transition temperature and to be a function of the rigidity of the polymer. ©1995 John Wiley & Sons, Inc.
Evolution of nanometer voids in polycarbonate under mechanical stress and thermal expansion using positron spectroscopy
Authors: Xie L. , Gidley D. W. , Hristov H. A. , Yee A. F.
Published: April 2003

Positron Annihilation Lifetime Spectroscopy (PALS) measurements were conducted on polycarbonate subjected to either thermal expansion or to tensile and compressive strains. It was found that thermal expansion affected both the nanometer hole size and the hole number density, whereas mechanical stress affected mainly the size of existing holes, and did not generate or eliminate holes in the quasielastic deformation region. The effect of stress on yield and postyield behavior of this glassy material was also investigated. The deduced hole volume fraction of this polymer at 25°C was 6.8 ± 0.5% from the thermal expansion experiment and 7.2 ± 1.2% from the mechanical loading experiment. When the specimen was under compression, the hole volume fraction was found to continuously decrease. This can be considered as evidence of the inability of the free volume concept in explaining the yield behavior of glassy polymers. ©1995 John Wiley & Sons, Inc.
Charge effect of the cation on the structure and the molecular mobility of polymer electrolytes
Authors: Bartolotta A. , Di Marco G. , Lanza M. , Carini G.
Published: April 2003

A study of the thermal and mechanical characteristics of polyethylene oxide‐Fe(SCN)3 complexes shows the existence of structures which can be described by considering a crystalline phase of pure polyethelene oxide (PEO) and an amorphous phase of PEO with dissolved salt. Increasing salt contents decrease the content of crystals, favoring the formation of complexes with a high degree of noncrystallinity as a result of strong polymersalt interactions which tend to enhance the distortion degree of the polymeric skeleton. The microscopic homogeneity of the complexes is also confirmed by the presence in the thermal and mechanical spectra of single glass transitions, which shift to higher temperatures with increasing salt content. Two molecular relaxations are present in the mechanical behavior of these systems, the γ‐and the αa‐processes at low and high temperatures, respectively, and show a relaxation strength which increases with decreasing degree of crystallinity of the polymer up to a X ∼ 0.10 molar fraction. Both relaxations exhibit a marked nonexponentiality which has been well accounted for in terms of a gaussian distribution of relaxation times for the γ‐process and of the Kolrausch‐Williams‐Watt exponential function for the αa‐process. In the glassy region, the elastic modulus E' reveals a linear temperature dependence which has been interpreted as arising from the anharmonicity of vibrational modes. Increasing noncrystallinity of the system gives rise to an increase of the anharmonicity parameter, which has been ascribed to the influence of the “free volume” in determining the thermal expansivity. ©1995 John Wiley & Sons, Inc.
Membrane formation by isothermal precipitation in polyamide‐formic acid‐water systems I. Description of membrane morphology
Authors: Cheng Liao‐Ping , Dwan An‐Hwa , Gryte Carl C.
Published: April 2003

Aliphatic polyamides (Nylon‐66 and a Nylon‐6, ‐66, ‐610 terpolymer) were isothermally precipitated from formic acid solution by immersing in an aqueous nonsolvent bath or a solvent/nonsolvent mixture. Depending on the composition of the polymer solution and nonsolvent bath, phase separation by nucleation and growth can be initiated for a liquid‐liquid phase separation process, a crystallization process or a combined process. Under certain conditions, crystallization of Nylon‐66 results in a membrane with a uniform skinless microporous structure that was rapidly wetted by water. In contrast, liquid‐liquid phase separation produces a polyamide film with largely unconnected cellular voids that is as a result not wetted by water. © 1995 John Wiley & Sons, Inc.
A thermally stimulated discharge currents study of the molecular motions in two polysiloxane side‐chain liquid crystalline polymers
Authors: Mano João F. , Correia Natália T. , Moura Ramos Joaquim J. , Fernandes Anabela C.
Published: April 2003

The technique of thermally stimulated depolarization currents was used to study the dipolar relaxation mechanisms in two side‐chain liquid‐crystalline polysiloxanes. The studied polymers have the same mesogenic side‐group, but they differ in the number (or density) of side groups attached to the main chain. In both cases three different relaxations were observed: one in the vitreous state, one in the liquid crystalline phase, and the glass transition relaxation. The features of those thermally stimulated discharges are discussed and some suggestions are made concerning the attribution of those discharges at the molecular level. © 1995 John Wiley & Sons, Inc.
Polyurethane cationomers III: Oxygen permeation
Authors: Chan Wu‐Chung , Chen Show‐An
Published: April 2003

Dynamic oxygen permeation measurements at 20–70°C on films cast from solutions and emulsions of three series of polyurethane (PU) cationomers based on MDI, HDI, and TDI that are the subject of Parts I and II of this series were made by Barrer's vacuum technique. For the MDI system, films cast from solutions of ionized PU exhibit permeation coefficients P that are higher at 20–40°C (below the glass transition temperature Tgh of the hard domains) than at 50–70°C (above Tgh) by factors of about 5 and 40. This is the opposite of what is observed for normal homopolymers and un‐ionized PU. This phenomenon is attributed to the continuous/dispersed morphology of these films. At the low temperature, oxygen molecules diffuse through the continuous phase (soft domains) only. But at the high temperature, oxygen molecules diffuse through soft domains and subsequently through hard domains, leading to an increase in diffusion pathlength. For films cast from the PU emulsions, such a drop in P was not observed because the hard domains were partially inverted from the dispersed phase to a continuous phase that gives an interwoven morphology. Such morphology allows oxygen molecules to diffuse through soft and phase‐inverted hard domains simultaneously. For the HDI and TDI systems, P and D vs. 1/T plots show no zone of discontinuity. This is attributed to a Tgh that is lower than or close to the permeation temperature. © 1995 John Wiley & Sons, Inc.
Chemical modification of butyl rubber. II. Structure and properties of poly(ethylene oxide)‐grafted butyl rubber
Authors: Ikeda Yuko , Kodama Kazutoshi , Kajiwara Kanji , Kohjiya Shinzo
Published: April 2003

Poly(ethylene oxide)‐grafted butyl rubbers (IIR‐g‐PEOs), which were synthesized from potassium salt of polyethylene glycol monomethyl ether (PEGM) and chlorinated butyl rubber, were found to behave like thermoplastic elastomers. The poly(ethylene oxide) (PEO) content of these amphiphilic polymers was ca. 10 wt %, and their PEO lengths were 750, 2000, and 5000, respectively. The grafted segments of PEO in butyl rubber (IIR) aggregated to form the PEO domains in IIR matrix. At constant PEO content, the longer the PEO segment length, the larger the size and the crystallinity of PEO domains became. This PEO domain worked as a cross‐linking site and a reinforcing filler. The degree of swelling in water of IIR‐g‐PEO film that was prepared from PEGM‐5000 was largest, but its emulsification ability was smallest among them. © 1995 John Wiley & Sons, Inc.
Prediction of polymer PVT behavior using the group contribution lattice‐fluid EOS
Authors: Parekh Vipul S. , Danner Ronald P.
Published: April 2003

A scheme has been developed using the group contribution lattice‐fluid equation of state (GCLF‐EOS) to predict the pressure‐volume‐temperature (PVT) behavior of polymers in the amorphous state. The model requires only the structure of the molecule as input information. Prediction results with an average error of 2% have been obtained for a wide variety of polymers. A table of 23 different group contributions is presented. With this set of group parameters, the GCLF‐EOS can be applied in the prediction of equation of state properties of a wide variety of homopolymers, random copolymers, and polymer blends. © 1995 John Wiley & Sons, Inc.
Thermal diffusion and molecular weight calibration of poly(ethylene‐co‐vinyl acetate)s by thermal field‐flow fractionation
Authors: Jeon Sun Joo , Lee Dai Woon
Published: April 2003

Copolymer characterization is accomplished with respect to measurement of thermal diffusion coefficient (DT) and molecular weight determination by thermal field‐flow fractionation. The examined copolymers are the eight poly(ethylene‐co‐vinyl acetate)s [P(E‐V)] having different compositions of vinyl acetate ranging from 25 to 70% and the molecular weight from 110,000 to 285,000, and three polyvinyl acetate standards as component homopolymer. The carrier solvents are tetrahydrofuran, toluene, and chlorobenzene which have different viscosities and thermal conductivities. Measured DT values vary from 1.36 × 10−8 to 5.97 × 10−8 cm2/(s . K) which are dependent on the composition of copolymers and types of carriers. These values increase linearly with the increase of weight percent of vinyl acetate. It is possible to estimate DT values of polyethylene from the extrapolated intercept in the plots of DT vs. vinyl acetate wt % of copolymer. Tetrahydrofuran is found to be the appropriate carrier solvent for the separation of P(E‐V) copolymers since DT varies greatly with the increase of wt % in THF. Attempts are made to correlate the measured retention data with molecular sizes of copolymers for the construction of the molecular weight calibration curve. Good correlations (r2 ≥ 0.931) are found in which D/DT values of polymers vary inversely with the product of hydrodynamic volume by weight ratio of vinyl acetate. Based on this relationship, the unknown molecular weight of copolymer sample can be determined from component homopolymers for which standards are readily available. © 1995 John Wiley & Sons, Inc.
Rheological and mechanical properties of antiplasticized and rubber‐toughened bisphenol A polycarbonate
Authors: Kambour R. P. , Caraher J. M. , Fasoldt C. L. , Seeger G. T. , Sowa N. M. , White D. M.
Published: April 2003

The addition of a high‐Tg aromatic diluent to bisphenol A polycarbonate (PC) reduced Tg and melt viscosity while raising elastic modulus and yield stress substantially. Ultimate tensile elongation and impact toughness were badly affected. However, the addition to these antiplasticized blends of a small amount of a rubber modifier restored impact toughness and elongation but left the blend with increased melt fluidity and ambient stiffness re: neat PC. The key to this rebalancing of the properties of PC was found to be the disappearance of the plane strain crack instability that is a hallmark of the neat resin. The deformation mechanism in all the rubber‐containing blends in all failure tests, regardless of geometric constraint and strain rate was found to be shear flow alone. The large plastic zone seen at the plane strain crack tip appears to involve rubber particle cavitation as well. © 1995 John Wiley & Sons, Inc.
Impedance spectroscopy of reactive polymers. 2. Multifunctional epoxy/amine formulations
Authors: Bellucci Francesco , Valentino Maio , Monetta Tullio , Nicodemo Luigi , Kenny Jose , Nicolais Luigi , Mijovic Jovan
Published: April 2003

Dielectric measurements were utilized to follow the advancement of cure in a bifunctional and a tetrafunctional epoxy/amine formulation. In deferance to earlier dielectric studies of cure, complex impedance was measured and used to calculate ionic resistivity. By using complex impedance we were able to separate, according to their frequency dependence, the contributions to overall polarization from electrode blocking layers, mobile charge carriers, and dipole relaxations. At any stage of cure, there is a unique frequency at which ionic resistivity can be singularly measured. Our approach does not involve trial‐and‐error frequency search, it measures dielectric response in real time, and is conducive to the development of phenomenological models based on equivalent circuits. Values of ionic resistivity measured at different cure time and temperature were used to quantify the progress of cure. Excellent agreement was reported between the calculated values of normalized degree of cure obtained by dielectric and calorimetric measurements. It was suggested that apart from the extrinsic conductivity by ionic impurities, an intrinsic mechanism which involves the reactive molecules contributes to the overall ionic conductivity. © 1995 John Wiley & Sons, Inc.
Effects of humidity, imidization history, and thickness on water sorption behavior of poly(p‐phenylene biphenyltetracarboximide) films
Authors: Ree M. , Han H. , Gryte C. C.
Published: April 2003

Poly(p‐phenylene biphenyltetracarboximide) films with various thicknesses were prepared from the poly(amic acid) precursor by thermal imidization at 230–400°C for 1–10 h under a nitrogen atmosphere. The water sorption in the films was measured at 25°C over 22–100% relative humidity using a Cahn microbalance as a function of film thickness and thermal imidization history. The water diffusion in all the films followed nearly Fickian process despite the morphological heterogeneity due to the ordered and less ordered phases. The diffusion coefficient and water uptake varied in 0.85 × 10−10 − 7.50 × 10−10 cm2/s and 0.12–2.4 wt %, respectively, depending upon humidity, film thickness, and imidization history. Both diffusion coefficient and water uptake increased with increasing humidity, but decreased as imidization temperature and time increased. With increasing film thickness, the diffusion coefficient increased whereas the water uptake decreased. The water sorption behavior was interpreted with the consideration of morphological variations, such as polymer chain order, in‐plane orientation, and intermolecular packing order due to the film thickness and imidization history. © 1995 John Wiley & Sons, Inc.
A thermally stable polymer molecular composite
Authors: Roberts Michael F. , Jenekhe Samson A.
Published: April 2003

A molecular composite of rigid‐rod poly(p‐phenylene benzobisthiazole) and flexible‐coil poly(benzimidazobenzophenantroline) has been prepared, characterized, and shown to be thermally stable to at least 300°C. These results suggest that stable miscible blends of rodlike and coil‐like polymers can be prepared by controlling the glass transition temperature of the flexible‐coil polymer. © 1995 John Wiley & Sons, Inc.
Isothermal cis‐trans isomerization behavior of polyacetylene films
Authors: Kyotani H. , Shimomura M. , Ito K. , Tanabe Y. , Zhang Y.‐X. , Akagi K. , Shirakawa H.
Published: April 2003

Isothermal cis‐trans isomerization behavior was studied by differential scanning calorimetry for conventional Shirakawa polyacetylene (S‐PA) film and highly stretchable polyacetylene (hs‐x) films synthesized using catalysts aged at high temperature. The rate of isomerization is slower for S‐PA than for hs‐x. Kinetic results of isomerization are analyzed by a stretched exponential function with exponent n (0 < n < 1), which is different from the previously assumed single exponential function. An activation energy of 31 kcal/mol was obtained for all the samples. © 1995 John Wiley & Sons, Inc.
Phase behavior and miscibility limits in PC/hytrel blends
Authors: Gaztelumendi M. , Nazabal J.
Published: April 2003

Polycarbonate of bisphenol‐A (PC)/copolyetherester (Hy) blends have been obtained by melt mixing over the complete composition range. After testing the lack of interchange reactions and degradation under the conditions studied, the miscibility state was studied by DSC and DMTA. The blends appeared to be miscible in the melt state. A fairly complex phase behavior was obtained in the solid state with Tg‐composition plots showing a single Tg at most of the compositions but very different after the first and second scans. This was attributed to the different crystalline content of the blends before the two scans. The presence of a Hy crystalline phase and a single PC/Hy amorphous phase in all the blends, with the exception of the 20/80 composition, was verified by DMTA. Several thermal treatments showed the presence of an immiscibility range and, thus, the presence of a UCST. A LCST, which in the case of the 50/50 and 40/60 blends would be at roughly 75°C, will also probably exist. © 1995 John Wiley & Sons, Inc.
Highly conducting solid electrolytes based on poly (ethylene oxide‐co‐propylene oxide)
Authors: Florjańczyk Zbigniew , Krawiec Włodzimierz , Wieczorek Władysław , Siekierski Maciej
Published: April 2003

The conducting properties of solid electrolytes comprising random poly(ethylene oxide‐co‐propylene oxide) (of 84 : 16 monomer units mole ratio) and lithium, sodium, potassium, cesium, and rubidium salts have been studied. The systems containing some lithium or sodium salts achieved conductivity levels as high as 10−5–10−4 S/cm at ambient temperature and greater than 10−3 S/cm at 100°C. However, the systems with rubidium and cesium salts exhibit conductivities a few orders of magnitude smaller. DSC studies show that the electrolytes studied are characterized by a high content of an amorphous phase (95–100%). It is suggested that the copolymer exhibits lower complexing abilities than that of poly(ethylene oxide), which results in a higher flexibility of electrolytes containing small cations and poor dissociation of the salts having large cations. © 1995 John Wiley & Sons, Inc.
Structural models for homogeneous organic‐inorganic hybrid materials: Simulations of small‐angle X‐ray scattering profiles
Authors: Landry Michael R. , Coltrain Bradley K. , Landry Christine J. T. , O'Reilly James M.
Published: April 2003

Two morphological models have been proposed to describe small‐angle x‐ray scattering from organic‐inorganic composite (OIC) materials. The first model invokes the idea of a liquid‐like arrangement among noninterpenetrating fractal clusters, and the second employs an empirical correlation function that would be expected for a bicontinuous two‐phase (B2P) picture with the inorganic portion exhibiting fractal characteristics. Simulated scattering profiles have been generated for direct comparison with experimental data. The samples studied were a triethoxysilane‐endcapped bisphenol A epoxide resin (EAS) reacted in the presence of tetraethoxysilane (TEOS) under slightly basic conditions, and a random trimethoxysilane‐functionalized copolymer of poly(methyl methacrylate) (MMA‐TMS) with added tetramethoxysilane (TMOS), reacted in an acidic medium. Each morphology model qualitatively simulates the broad scattering maximum and limiting high‐angle slope commonly seen in SAXS profiles. It is concluded that the inorganic phase in the EAS hybrid exhibits particle‐like characteristics at length scales less than approximately 250 Å, and the organic and inorganic components are bicontinuous at larger distances. The MMATMS composite is better described by bicontinuous organic and inorganic phases with a periodic fluctuation of about 40 Å. The scattering maximum arises either from the mean separation of particles or a dominant wavelength in a concentration fluctuation, similar to that observed for spinodal decomposition. In either case, the SAXS peak position is related to the distance between junction points of the crosslinked organic polymer. © 1995 John Wiley & Sons, Inc.
Magic angle carbon‐13 NMR study of solid poly(ethylene naphthalene‐2,6‐dicarboxylate)
Authors: Abis Luigi , Merlo Edoardo , Po' Riccardo
Published: April 2003

Amorphous (1) and semicrystalline (2) samples of poly(ethylene naphthalene‐2,6‐dicarboxylate) (PEN) have been investigated by cross‐polarization/magic angle spinning (CP/MAS) 13C NMR at 26°C (1 and 2), 100°C (1) and 120°C (2) in order to study the phase structure and the local motion of polymer chain segments at temperatures below and close to Tg (120°C). The lineshape of the ethylene unit 13C signal in sample 2 is consistent with the presence of two components which were assigned to trans and gauche conformations. The first component arises mainly from the crystalline regions and the second one from the amorphous part. Cross‐polarization curves were traced by changing the contact time between carbon and proton reservoirs. TCH (cross relaxation time) and proton T1p (spin‐lattice relaxation time in the rotating frame) values were obtained as best fit parameters by fitting calculated curves to the experimental data. All 13C NMR data are consistent with the presence of highly rigid ethylene units in both semicrystalline and amorphous samples within the temperature range (T) investigated. This result is in disagreement with the 1H NMR wide line spectra which showed a noticeable narrowing of the linewidth with increasing temperature in the same range, hence indicating a great mobility of the chain segments. To account for this discrepancy a qualitative model based on the existence of two distinct dynamic regions, one where motion is highly restricted and the other one where large reorientations of ethylene group torsional angles take place, is suggested. The NMR results led to the conclusion that three structural phases are present in PEN: crystalline, very rigid amorphous, and very mobile amorphous. © 1995 John Wiley & Sons, Inc.
Morphology and electro‐optic responses of poly(methyl methacrylate)/nematic liquid crystal composite films: Effect of the polymer molecular weight
Authors: Kim B. K. , Ok Y. S. , Choi C. H.
Published: April 2003

The director configuration, state of liquid crystal (LC) phase aggregation, and the electooptic properties of thin polymer films of poly(methyl methacrylate) (PMMA) containing nematic liquid crystal have been studied. Measurements included scanning electron micrograph (SEM), polarized optical micrographs (POM), and transmittance response of the film with the applied electric AC voltage and frequency. Two types of PMMA with significantly different molecular weight (Mw) were used, and the effects of polymer molecular weight on morphology and electro‐optic properties of the composite films were examined. © 1995 John Wiley & Sons, Inc.
Calculating poly(ethylene‐co‐acrylic acid)‐solvent phase behavior with the SAFT equation of state
Authors: Hasch Bruce M. , McHugh Mark A.
Published: April 2003

Statistical Associating Fluid Theory (SAFT) is used to model the cloud‐point behavior of poly(ethylene‐co‐acrylic acid), with up to 7 mol % acid content, in propane, butane, propylene, butene, and dimethyl ether at temperatures to 250°C and pressure to 2600 bar. The values for the pure component temperature‐independent segment volumes, nonspecific interaction energies, and the numbers of segments per molecule are equal to those used for polyethylene, because these copolymers contain modest amounts of acrylic acid repeat units. Two different approaches are used to determine values of the pure component energy of hydrogen bonding, ϵ/k, and the binary interaction parameter, kij. In one approach, ϵ/k for acid dimerization is obtained from literature spectroscopic data and a constant value of kij is fit to each copolymer‐solvent cloud‐point curve. Increasing the value of kij shifts the predicted cloud‐point curves to higher temperatures and pressures. For the five solvents used in this study, kij decreased steadily in the range of 0.040 to −0.025 as the acid content in the copolymer increased. The predicted cloud‐point curves are in good agreement with experimental data, and the impact of hydrogen bonding on the phase behavior is well represented, even if kij is set equal to zero. For the second approach, ϵ/k is set to ∼ 90% of the value obtained from spectroscopic data as determined from a fit of a single poly(ethylene‐co‐acrylic acid)‐butane cloud‐point curve, while kij is fit to the corresponding polyethylene‐solvent system. This approach requires less mixture data than the previous approach, and the calculated cloud‐point curves are also in good agreement with experimental data, except for the EAA‐DME systems. © 1995 John Wiley & Sons, Inc.
The ionic conductive property of sulfonated polyethylene oxide polyurethane ionomers
Authors: Xu Hai‐Sheng , Yang Chang‐Zheng
Published: April 2003

A series of lithium and sodium salts of sulfonated polyethylene oxide (PEO) polyurethane ionomers in different levels of ionization were prepared. It has been found that this material is a new type of ionic conductive polymer, characterized by a single‐ion transport mechanism and good mechanical properties. The ionization level significantly influences the ionic conductivity of the samples. When the mole ratio of the metal ion and ether oxygen atom is about 0.05, the ionomers exhibit maximum cationic conductivity. An optimal cationic conductivity of 1.0 × 10−5 S/cm is obtained at about 70°C without any addition of organic plasticizer. The conductivity increases apparently when propylene carbonate and low MW PEO are added to the polyurethane ionomer. © 1995 John Wiley & Sons, Inc.
Plasticization and crystallization of cis‐1,4 polyisoprene mixed with methyl linolate
Authors: Kawahara Seiichi , Tanaka Yasuyuki
Published: April 2003

Crystallization behavior of synthetic cis‐1,4 polyisoprene mixed with methyl linolate was investigated by differential scanning calorimetry and dilatometry. At isothermal crystallization temperature of −25°C, a rate of crystallization decreased with the addition of 1 wt % methyl linolate, whereas it increased with a large amount of methyl linolate, about 30% by weight. Although Avrami constant of cis‐1,4 polyisoprene was 2.82, that of mixtures containing 1 and 30 wt % methyl linolate was found to be approximately 4. This implies the same crystallization mechanism was in operation in the mixtures. Since glass transition temperature, Tg, of cis‐1,4 polyisoprene decreased as the methyl linolate content of mixture increased, methyl linolate was found to be plasticizer for cis‐1,4 polyisoprene. The increase in the rate of crystallization in the mixtures was corresponding to the decrease in Tg. © 1995 John Wiley & Sons, Inc.
Molecular weight distribution by stirring‐induced fractional precipitation
Authors: Habibe Maria Eunice S. , Esperidião Maria Cecilia A.
Published: April 2003

Ultrahigh molecular weight polyethylenes GUR, UTEC 2540, and UTEC 3540 were fractionated by precipitation from cooling of solutions with stirring [stirring‐induced fractional precipitation (SIFP)]. The samples were dissolved in decalin and precipitated over the temperature range of 100‐78°C. Three types of procedures were investigated. From fractionation data, the integral and differential molecular weight distribution (MWD) of the polymer were calculated. The MWD and average molecular weights, $\bar M_w$ and $\bar M_n$, by size exclusion chromatography (SEC) and the limiting viscosity number of the fractions and whole polymer were determined. From these data, the Mark‐Houwink constants were calculated. The ‘K’ and ‘aη’ values obtained were 6.70 × 10−4 and 0.69, respectively. The MWD curves calculated from SIFP technique by using these constants are in accordance with the MWD by SEC. Fractionation depended on the chemical nature of the stirrer and the cooling rate of the solution during precipitation. The methodology is reproducible. Faster fractionation was observed compared with other methods. © 1995 John Wiley & Sons, Inc.
Thin films of nylon 13,13 casted on water: Morphology and properties
Authors: Wang Li Hui , Porter Roger S.
Published: April 2003

Substrate‐free thin film of Nylon 13,13 has been prepared continuously by casting the polymer on a water surface from m‐cresol solution. The uniform thickness of film is ca. 500 A, as measured with a Profilometer. Film morphology and properties have been characterized by transmission electronic microscopy (TEM), x‐ray photoelectron spectroscopy, wide‐angle x‐ray scattering, differential scanning calorimetry and by contact angle measurements. Results show that there is no preferential accumulation of the amide group toward the water surface. A spherulite structure exists in this film with a crystallinity of 26% by DSC. Fibers were drawn from the films which had a tensile modulus of 5 GPa, stiffer than reported for this nylon as prepared by other means. Other members of the nylon series, such as Nylon 6, Nylon 12, have also been prepared in films by the same casting method under modified conditions. © 1995 John Wiley & Sons, Inc.
Ionic conduction in LiSCN/dimethylformamide/poly(propylene oxide) system I. Dissociation equilibria of LiSCN
Authors: Mitani Kazuishi , Adachi Keiichiro
Published: April 2003

Dissociation equilibria of lithiumthiocyanate (LiSCN) in N,N‐dimethylformamide (DMF) solutions of poly (propylene oxide) (PPO) were investigated by using infrared spectroscopy. The stretching bands due to the thiocyanate ions SCN−1 and the LiSCN ion pair were found at 2058 and 2072 cm−1, respectively. At high LiSCN concentration C of ca. 20 wt %, another weak band due to the dimer (LiSCN)2 was observed. From the ratio of the areas of the absorption bands, the dissociation constant K1 for the equilibrium LiSCN ↔ Li+ + SCN−1 and that K2 for (LiSCN)2 ↔ 2LiSCN have been determined. With increasing DMF content, K1 increases from 1 × 10−4 for bulk PPO to 4.8 × 10−1 for pure DMF at 299 K. Log K1 is not linear against inverse of the dielectric constant ϵ of the medium and decreases with increasing temperature. The enthalpy (ΔH) and entropy (ΔS) changes for the dissociation of LiSCN are both negative. ©1995 John Wiley & Sons, Inc.
Solubility and transport of water vapor in some 6FDA‐based polyimides
Authors: Lokhandwala K. A. , Nadakatti S. M. , Stern S. A.
Published: April 2003

Permeability, diffusion, and solubility coefficients for H2O vapor in four different 6FDA‐based polyimides were determined at temperatures between 25 and 45°C and over a wide range of relative humidities. The solubility of H2O vapor in some of the polyimides studied can be described by the “dual‐mode sorption” model whereas in other polyimides it is represented by the Flory‐Huggins equation, which suggests that the latter polymers are plasticized by H2O. The solubility of H2O vapor in the polyimides decreases as the temperature is raised and increases with increasing polarity of the polymer. The diffusion coefficients for H2O in the polyimides studied either increase or pass through a weak maximum with increasing H2O activity, or concentration in the polymers. The latter behavior is probably due to a clustering of H2O molecules in the polyimides at higher H2O activities or concentrations. The diffusion coefficients for H2O decrease as the chain‐packing density of the polyimides increases. The permeability coefficients for H2O vapor in 6FDA‐based polyimide membranes either increase slightly or are constant as the H2O activity is increased. The experimental values of the permeability coefficients are consistent with the values determined from diffusion and solubility coefficients. The permeability of the polyimides to H2O vapor appears to be controlled by the solubility of H2O in the polymers. The polyimides studied exhibit a very high selectivity for H2O vapor relative to CH4, and therefore are potentially useful membrane materials for the dehydration of natural gas. ©1995 John Wiley & Sons, Inc.
Ultrasonic properties of PVC (S‐27/R63) in the glassy region
Authors: Guney H. Yüksel , Oskay Taner , Özkan H. Sinan
Published: April 2003

The ultrasonic properties of PVC (S‐27/R63) in the glassy region have been investigated as a function of temperature. The propagation velocities and absorption of the longitudinal and transverse ultrasonic waves have been measured at constant frequency of 2 MHz and at temperatures varying between −5°C and 75°C, using the ultrasonic immersion technique. The variation of the elastic moduli with temperature has been derived from these measurements. The results thus obtained have been compared to those previously published in the literature for different PVC and other polymer samples. ©1995 John Wiley & Sons, Inc.
Rationalization of the ratio of excimer‐to‐monomer fluorescence emission intensity in bichromophoric diesters of 1‐pyrenoic acid and mono‐, di‐, tri‐, and tetraethylene glycols
Authors: Martin Olga , Mendicuti Francisco , Saiz Enrique , Mattice Wayne L.
Published: April 2003

The ratio of excimer to monomer emission intensities, denoted by ID/IM, was measured for Py–COO(CH2CH2O)mCO  Py, where Py denotes the 1‐pyrenyl group and m = 1–4, in solvents of different viscosity, η. Three different systems were used to change the viscosity of the medium: (a) Mixtures of methanol and ethylene glycol at 25°C, (b) linear aliphatic alcohols, H(CH2)nOH, where n =1–6, also at 25°C, and (c) ethylene glycol over the range 6.6–35°C. The ratio ID/IM decreases sharply as η increases, and the rate of the decrease in ID/IM is a function of m. Quantitatively, the dependence of ID/IM on η at high viscosity, i.e., the slope [d(ID/IM)/d(1/η)]∞, is larger in the present work than in another series of 1‐pyrenyl diesters in which the flexible spacer is an oligomer of polyethylene, instead of an oligomer of polyoxyethylene. In the limit where η → ∞, the ratio ID/IM assumes its largest value in the bichromophoric compound with m = 2. However, as η decreases the compound with m = 3 becomes the one with the largest ID/IM. A complete rotational isomeric state analysis (for the compounds with m = 1–3) and a Monte Carlo simulation (for the compound m = 4) of the conformations of the diesters can rationalize the behavior of ID/IM in the high viscosity limit. ©1995 John Wiley & Sons, Inc.
Surfactant exudation in the presence of a coalescing aid in latex films studied by atomic force microscopy1
Authors: Juhué Didier , Wang Yongcai , Lang Jacques , Leung On‐Man , Goh M. Cynthia , Winnik Mitchell A.
Published: April 2003

We report atomic force microscopy images of surfactant (SDS) exudation in PBMA latex films, in the presence and the absence of a coalescing aid (Texanol™, TPM). The exudates appear as hilly islets, and at times as mountains, at the film surface. Their size and number increase upon annealing above the glass‐transition temperature of the latex polymer. TPM was found to be a strong promoter of surfactant exudation at the air‐polymer interface. In the absence of TPM, annealing the films for several hours at 70°C led to very little migration of surfactant to the surface at most sites in the film. When the films with structures of SDS on their surface were immersed in water, these structures disappeared. Pores, ranging in size from tens to hundreds of nm in diameter, were clearly visible in the surface of the films. These films dry from the edges of the film inward, with a propagation front concentrating the water‐soluble species into a turbid, moist region in the center. At this site, the rate at which the surfactant comes to the surface is enormously enhanced over that at other sites in the film. This is likely due to the high concentration of surfactant in this region, transported there by the drying process. © 1995 John Wiley & Sons, Inc.
Gas transport properties of polyarylates part I: Connector and pendant group effects
Authors: Pixton M. R. , Paul D. R.
Published: April 2003

Gas transport of helium, hydrogen, oxygen, nitrogen, methane, and carbon dioxide gases in a series of polyarylates based on isophthalic acid has been examined. These polyarylates were prepared from bisphenol A, hexafluorobisphenol A, phenolphthalein, and fluorene bisphenol monomers to study the effects of varying the bisphenol connector group size and shape. Substitution of a tertiary butyl group at position five on the isophthalate ring increases polymer permeability. The incorporation of a large, bulky connector group increases gas permeability and maintains permselectivity while the substitution of t‐butyl groups increases gas permeability by two‐ to fourfold but lowers permselectivity. Most of the increases in permeability can be related to increases in the diffusion coefficients of all the gases. All the polyarylates have high glass transition temperatures and may be suitable for high temperature gas separation applications. ©1995 John Wiley & Sons, Inc.
1H NMR studies of molecular relaxations of poly‐1‐butene
Authors: Maring D. , Meurer B. , Weill G.
Published: April 2003

The temperature dependance of the proton NMR line shape, T1 and T1ρ of isotactic poly‐1‐butene forms I, I′, II, and III have been studied between 100 and 400 K (up to melting). The usual line shape decompositions concerning rigid vs. crystalline and mobile vs. amorphous phases are discussed. The rigid‐lattice second moments were calculated introducing a fast rotation of the methyl group.

Complex spin‐lattice decays were analyzed as a continuous distribution of rates. Relaxation behavior was analyzed in terms of a Williams‐Watt correlation function. Motions in the crystalline parts of samples in forms II and III very similar to the amorphous one were revealed, leading us to compare form II to a condis crystal during the crystal form transformation. © 1995 John Wiley & Sons, Inc.
Relaxations in liquid crystalline poly(tetraethylene oxide terephthaloyl‐bis‐4‐oxybenzoate)
Authors: Gómez M. A. , Marco C. , Fatou J. M. G. , Suarez N. , Laredo E. , Bello A.
Published: April 2003

The relaxation behavior of poly(tetra ethylene oxide terephthaloyl‐bis‐4‐oxybenzoate), PTETOB, was analyzed by thermally stimulated depolarization currents, TSDC, and dynamic mechanical techniques, DMTA, and the results compared with those obtained by differential scanning calcrimetry, thermo‐optical analysis, and x‐ray diffraction. In the low temperature region, −173–30°C, three main transitions were observed and assigned to the γ relaxation, the glass transition of the mesophase and the glass transition temperature of the amorphous material. The complex behavior observed in the range 110–160°C was as signed to a crystal‐crystal transition which competed with the formation of a mesophase and afterward the formation of a smectic A mesophase. At higher temperatures, was observed the transition from the smectic A mesophase to a nematic one, prior to the isotropization temperature. In the TSDC experiments the formation of a permanent electret was detected and the charges trapped in the mesophase were canceled only at the isotropization temperature. © 1995 John Wiley & Sons, Inc.
Gas transport through ethylene‐acrylic acid ionomers
Authors: Nobile M. A. Del , Mensitieri G. , Nicolais L. , Weiss R. A.
Published: April 2003

Transport properties of several gases in two ethylene‐acrylic acid ionomers characterized by a different amount of acrylic acid groups and percentage of neutralization have been investigated. Sorption and permeation experiments have been performed with N2, O2, CO2, CH4, C2 H6, and SF6 in the 25–65°C range and with C3H8 only at 25°C. Gas permeabilities, diffusivities, and solubilities were evaluated along with activation energies and heats of solution. Data obtained in the present investigation were compared to analogous results reported in literature for polyethylene to better highlight the effect of ionic aggregates on the gas transport mechanism. © 1995 John Wiley & Sons, Inc.
Scattering properties of branched polymers in the high wave vector region and good solvent conditions
Authors: Benmouna M. , Borsali R. , Khaldi S.
Published: April 2003

Static and dynamic scattering properties of branched polymers in the high‐wave vector region and in good solvent conditions are derived. The treatment of Benoít et al. is extended to good solvent conditions by calculating explicitly the static intensity, including numerical factors. The dynamical properties are also examined and, in particular, the first cumulant of the intermediate scattering function is derived using the preaveraged Oseen tensor. The results are presented in terms of the critical exponent v to account for the effect of swelling due to excluded volume interactions. These interactions are introduced assuming that v is the same everywhere along the chain but ignoring all the refinements introduced by the renormalization group theories in the case of linear chains. © 1995 John Wiley & Sons, Inc.