bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermal expansion of the crystal lattice of novel thermoplastic polyimides
Authors: Brillhart Mark V. , Cebe Peggy 
Published: April 2003

AbstractMeasurements of the coefficient of thermal expansion (CTE) of the crystalline lattice of two semicrystalline thermoplastic polyimides are reported. NEW‐TPI and LARC‐CPI polyimides were studied using elevated temperature wide‐angle x‐ray scattering (WAXS) from 25°C. To 325°C. To examine possible shifts in the c‐axis, a novel approach developed in our lab was used to create highly oriented samples. Films were treated in 1‐methyl‐2‐pyrrolidinone (NMP) at the reflux temperature, washed and then dried under constraint. The films treated in this manner were highly oriented, with c‐axes preferentially aligned along the film normal. The advantage of this orientation is that it allows numerous reflections of type (00l) to be examined for temperature shifts of the c‐axis using reflection mode WAXS. No systematic shift of the c‐axis lattice parameter as a function of temperature was observed in either NEW‐TPI or LARC‐CPI. The c‐axis thermal expansion is concluded to be smaller than 8 x 10−6/°C for LARC‐CPI, and for NEW‐TPI may be weakly negative. From WAXS of unoriented films, systematic shifts in the a and b lattice parameters were deduced as a function of temperature. The linear CTEs relating these unit cell parameters at temperature T to their values at 0°C are:

©1995 John Wiley & Sons, Inc.
Structures of poly(p‐hydroxybenzoic acid) (PHBA) at ambient temperature
Authors: Iannelli Pio , Yoon Do Y. 
Published: April 2003

AbstractThe molecular structure of poly (p‐hydroxybenzoic acid) (C6H4COO)x at ambient temperature was determined by x‐ray powder diffraction analysis. The diffraction pattern is explained as a mixture of two orthorhombic phases having the same space group Pbc21 with four C6H4COO chemical repeats in the unit cell and the following cell parameters: a = 7.42 Å, b = 5.70 Å, and c = 12.45 Å for phase I (ρcalc = 1.51 g cm−3); and a = 3.83 Å, b = 11.16 Å, and c = 12.56 Å for phase II (ρcalc = 1.48 g cm−3). The chain conformation is the same in both phases, involving two benzoyl rings staggered by ca. 120° along the chain. Disorder has been considered in the packing of phase I by giving equal occupancy to the two molecules oriented up or down along the c chain axis. ©1995 John Wiley & Sons, Inc.
Memory effects in polymers. V. Processing history versus thermally induced self‐orientation of unoriented poly(chlorotrifluoroethylene) films
Authors: Khanna Y. P. , Kuhn W. P. , Macur J. E. , Messa A. F. , Murthy N. S. , Reimschuessel A. C. , Schneider R. L. , Sibilia J. P. , Signorelli A. J. , Taylor T. J. 
Published: April 2003

AbstractA peculiar phenomenon is reported whereby a melt‐extruded, low‐crystallinity, unoriented film of poly(chlorotrifluoroethylene) upon unconstrained thermal treatment, self‐extends in the machine direction (MD) while shrinking along the transverse (TD) and normal/thickness (ND) directions. In addition to the expected increase in crystallinity, the annealing process leads to an unexpected development of crystalline orientation along the MD. This phenomenon is an example of “processing‐induced memory effects” since it depends on the processing history of the starting film, e.g., melt‐extrusion leads to the subject behavior whereas compression molding does not. We must mention that the melt‐extruded films of poly(chlorotrifluoroethylene) are isotropic to start with, that is, MD and TD are indistinguishable prior to the annealing process. Furthermore, this phenomenon has not been observed for any other semicrystalline polymer and is believed to be the first citation for poly(chlorotrifluoroethylene) since its commercialization in 1957. Thermomechanical analysis (TMA) is the analytical technique that led to this novel phenomenon which was later substantiated by x‐ray diffraction (XRD). ©1995 John Wiley & Sons, Inc.
Slow crack growth in blends of HDPE and model copolymers
Authors: Zhou Z. , Brown N. , Crist B. 
Published: April 2003

AbstractThe resistance to slow crack growth (SCG) was measured in binary blends of high density polyethylene (HDPE) and 5–10% concentrations of model ethylene‐butene random copolymers by measuring the time to failure (tf) under a constant stress intensity. An increase of tf with the addition of the copolymer if the copolymer could crystallize and the increase was greater the higher branch density. The copolymer with 117 branches/1000C could not crystallize and therefore its blend had a tf that was less than that of the HDPE. The fracture energies of the blends as determined by their resistance to SCG were compared with the energy by rapid fracture, Jc, as previously measured by Rhee and Crist. It is concluded that SCG is more sensitive to variations in the microstructure than is rapid fracture and that the differences in SCG behavior can be qualitatively explained in terms of the differences in microstructure of the blends. ©1995 John Wiley & Sons, Inc.
Morphologies of microporous polyethylene and polypropylene crystallized from solution in supercritical propane
Authors: Pradhan Debjeet , Ehrlich Paul 
Published: April 2003

AbstractThe morphologies of solvent‐free, microporous, mechanically self‐supporting cylinders of linear polyethylene and isotactic polypropylene, crystallized from solution in supercritical propane, were examined by an SEM technique. The morphology of gels (or foams), obtained with little or no shrinkage from 2% to 35% solutions by weight of polyethylene (99% to 85% porosities), is shown in some detail. Lamellae with very little or considerable mutual organization occur, often in the form of stacks with straight or coiled axes (axialites). Further growth of these can lead to particles with a roughly spherical overall shape and a predominantly radial orientation of the lamellae at the particle surface. Subcooled isotactic polypropylene, on the other hand, crystallizes in the form of perfectly shaped birefringent microspheres of very uniform size. ©1995 John Wiley & Sons, Inc.
Molecular weight distribution in random crosslinking of polymer chains
Authors: Tobita Hidetaka 
Published: April 2003

AbstractThe molecular weight distribution (MWD) of crosslinked polymer molecules formed during polymeric network formation is the sum of the fractional MWDs containing 0, 1, 2, 3, … crosslinkages. The MWD for polymer molecules containing 𝓀 crosslinkages is investigated for the random crosslinking of polymer chains whose initial MWD is given by the Schulz‐Zimm distribution. For a very narrow initial MWD, each fractional MWD with 𝓀 = 0, 1, 2, … is independent and a multimodal distribution is obtained for the whole distribution. When the initial MWD is uniform, the average crosslinking density within the polymer fraction whose degree of polymerization is r, ρr is simply given by ρr = ρgel,c – 2/r irrespective of the extent of crosslinking reaction where ρgel,c is the crosslinking density within gel fraction at the gel point. On the other hand, the MWDs with 𝓀 crosslinkages overlap each other with different 𝓀 values significantly for the broader initial distributions, and ρr increases with the progress of crosslinking reactions. The value of ρr increases with increasing r but levels off asymptotically at large r. The average crosslinking density of polymer molecules containing 𝓀 crosslinkages ρ𝓀 is an increasing function of k but soon reaches a plateau; sooner for the broader initial MWDs. For 𝓀 ≥ 1, ρ𝓀 is always larger than the average crosslinking density of the whole reaction system ρ in the pregelation period, i.e., in terms of the crosslinking density, the difference between polymer molecules with and without crosslinkage is most significant. In general, the average crosslinking density ρ, which is convenient to use in describing the nature of the whole reaction system, cannot be considered as a characteristic degree of crosslinking for polymer molecules containing at least one crosslinkage. Consideration of the bivariate distribution of r and k reveals important aspects of the polymeric network formation that have been obscured in the conventional theories in which the averages including linear polymers are solely considered. © 1995 John Wiley & Sons, Inc.
Computer simulation of crystallization kinetics and morphology in fiber‐reinforced thermoplastic composites. III. Thermal nucleation
Authors: Mehl Nathan A. , Rebenfeld Ludwig 
Published: April 2003

AbstractA computer simulation has been used to predict crystallization kinetics and crystalline morphology in composite materials based on thermally nucleated crystallizable matrices. As demonstrated for athermally nucleated composites, the presence of reinforcing fibers increases the complexity of the system. Fibers are shown to have a dual effect on the spherulitic crystallization process. The influence that fibers have depends on the interplay between the enhancing effects that fibers have on nucleation and the depressing effects that fibers have on spherulitic growth. Fibers that do not provide additional nuclei to the system depress the rate of crystallization relative to an unreinforced polymer, while fibers that add nuclei to the system increase the rate of crystallization. The transcrystalline morphologies that develop in thermally nucleated fiber‐reinforced polymers are controlled primarily by the relative numbers of bulk and fiber nuclei. The extent of transcrystalline regions can be suppressed either by increasing the rate of bulk nucleation, or by decreasing the rate of fiber nucleation. Finally, the qualitative appearance of the morphology in the transcrystalline region was found to be indicative of the mode of fiber nucleation. © 1995 John Wiley & Sons, Inc.
Influence of morphology on the fracture toughness of isotactic polypropylene
Authors: Ouederni Mabrouk , Phillips Paul J. 
Published: April 2003

AbstractAn adaptation of the fracture toughness test method, the J‐integral technique, is described within the general framework of polymer fracture behavior. It is shown that there is a strong interaction between different morphological parameters in the way they affect the fracture behavior of isotactic polypropylene (iPP). The fracture toughness decreases with increasing crystallinity at a fixed spherulite size. The fracture toughness also decreases slightly with increasing spherulite size at a constant crystallinity, but this may not be a pure spherulite size effect. The use of a nucleating agent results in a very fine spherulitic structure but facilitates crack growth and reduces the material toughness beyond the crack initiation stage. This suggests that the material behavior is dictated by the increase in crystallization temperature caused by the presence of the nucleating agent and not by the change in spherulite size. © 1995 John Wiley & Sons, Inc.
Dilation kinetics of glassy, aromatic polyimides induced by carbon dioxide sorption
Authors: Wessling M. , Huisman I. , Boomgaard Th. v. d. , Smolders C. A. 
Published: April 2003

AbstractOver the past years, the equilibrium sorption of gases in polymers has been intensively studied. Mostly, glassy polymers were investigated because of their excellent selective mass transport properties. This work does not focus on the equilibrium sorption but on the kinetics to reach the equilibrium. We developed a new experimental method measuring the sorption‐induced dilation kinetics of a polymer film. Carbon dioxide and glassy, aromatic polyimides were chosen as model systems. Low‐pressure experiments demonstrate that the measured dilation kinetics represent the sorption kinetics. A significant delay between the sorption and dilation kinetics is based on the fact that dilation kinetics occurs simultaneously with the concentration increase in the center of the polymer film. High‐pressure experiments reveal significant differences in dilation kinetics compared to low‐pressure experiments. Generally, three regimes can be distinguished in the dilation kinetics: a first, fast volume increase followed by two much slower regimes of volume increase. The magnitude of fast and slow dilation kinetics strongly depends on the swelling history of the polymer sample. The results of the experiments are analyzed in the light of a model relating the fast dilation kinetics to a reversible “Fickian” dilation and the slower dilation kinetics to an irreversible, relaxational dilation. © 1995 John Wiley & Sons, Inc.
Structure, conformation, and motions of polytetrahydrofuran (PTHF) in the hexagonal form of the PTHF‐urea inclusion compound
Authors: Vasanthan Nadarajah , Shin I. Daniel , Tonelli Alan E. 
Published: April 2003

AbstractCombination of differential scanning calorimetry, x‐ray diffraction, Fourier transform infrared, and C‐13 nuclear magnetic resonance observations made on the crystalline inclusion compound (IC) formed between polytetrahydrofuran (PTHF) and urea (U), together with their comparison to identical observations performed on bulk semicrystalline samples of PTHF, have permitted an analysis of the conformations, motions, and environments available to PTHF chains in both solid‐state phases. The isolated PTHF chains occupying the narrow channels of the PTHF‐U‐IC are highly extended, though small rotational deviations averaging 24° from the nearly all trans, planar zig zag conformation of bulk crystalline PTHF chains produce some significant differences in their behaviors. PTHF chains in PTHF‐U‐IC possess much greater mobility than bulk crystalline PTHF chains as evidenced by C‐13 spin lattice relaxation times, T1, 50 times shorter (1.5 s) than observed for bulk crystalline PTHF chains (75 s). FTIR observations are consistent with very little specific interaction between guest PTHF chains and host urea matrix molecules and result in similar spectra for bulk and IC PTHF, except for the presence of the CH2 rocking vibration band at 745 cm−1 observed for bulk PTHF. The absence of this band in the IC PTHF can be understood by considering the symmetry of the all trans, planar zig zag conformation of bulk crystalline PTHF chains, which prevents the CH2 rocking mode from coupling with skeletal stretching and bending modes as occurs in the nonplanar, helical PTHF chains in PTHF‐U‐IC. © 1995 John Wiley & Sons, Inc.
Viscoelasticity and birefringence of polyisobutylene
Authors: Okamoto Hirotaka , Inoue Tadashi , Osaki Kunihiro 
Published: April 2003

AbstractThe complex Young's modulus, E*(ω), and the complex strain‐optical coefficient, O*(ω), were measured for polyisobutylene (PIB) over a wide temperature range near and above its glass transition temperature. The master curves could be constructed well for each function with the method of reduced variables. The shift factor, aT, for E*(ω) is the same as that for O*(ω). The ratio of the imaginary parts of O*(ω) and E*(ω), O″(ω)/E″(ω), takes an extremum, which has never been observed for other polymers. The relation between O*(ω) and E*(ω) cannot be described by a modified stress‐optical rule (MSOR) which has been found valid for various polymers. The basic concept of the MSOR. i.e., the chain orientation and the orientation of flat monomer units in the stretch direction, is not sufficient to describe the behavior of PIB and another origin of stress, presumably due to the fluctuation of local stress, should be included. This term does not contribute to the birefringence. The main maximum of tan δ is ascribed to the relaxation of the chain orientation in contrast with many other polymers, such as polyisoprene and polycarbonate, for which the maximum of tan δ is ascribed to the rotational relaxation of monomer units. © 1995 John Wiley & Sons, Inc.
Metal particle adsorption and diffusion in a model polymer/metal composite system
Authors: Shull Kenneth R. , Kellock Andrew J. 
Published: April 2003

AbstractWe have developed a model polymer/metal composite system based on the adsorption of colloidal gold particles from a dilute aqueous suspension to the surface of poly(2‐vinylpyr‐idine) (PVP). Particle coverages and tracer diffusion coefficients for the particles within a PVP matrix phase were measured by Rutherford backscattering spectrometry. The adsorption process is quantitatively described by a diffusion‐limited mechanism where gold particles irreversibly adsorb to the surface of the polymer film. Model dispersions produced in this way are excellent model systems for studying the fundamental properties of metal particle dispersions, since the particle size and the areal density of particles on the surface are well‐controlled. Diffusion coefficients for the gold particles within PVP were also measured. The diffusion of the gold particles was found to be coupled to the bulk viscosity of the polymer, even though the size of the gold particles was only slightly larger than the mesh size of the entanglement network for PVP. © 1995 John Wiley & Sons, Inc.
Molecular weight characterization of soluble high performance polyimides. 2. Validity of universal SEC calibration and absolute molecular weight calculation
Authors: Konáš Martin , Moy Thomas M. , Rogers Martin E. , Shultz Allan R. , Ward Thomas C. , Mcgrath James E. 
Published: April 2003

AbstractSix different soluble high‐performance aromatic polyimides, each prepared by solution imidization to three controlled average molecular weights, were analyzed by size exclusion chromatography (SEC) using on‐line parallel coupled refractometric and viscometric detectors. N‐methylpyrrolidone (NMP) with 0.06 M LiBr and NMP stirred over P2O5 were used as mobile phase for four of the polyimides; NMP with 0.06 M LiBr and NMP stirred over P2O5 were used as mobile phases for four of the polyimides; NMP with 0.06 M LiBr tetrahydrofuran (THF) and chloroform served as mobile phases for the other two polyimides. For all the samples the stationary phase in the SEC columns was cross‐linked polystyrene beads. Molecular weight averages of the polyimides were calculated using universal SEC calibration with polystyrene standards in each solvent. The agreement of the calculated molecular weight averages in the different solvents confirms that the universal SEC calibrations are valid for these semiflexible polymers. There was good agreement with weightaverage molecular weights obtained by low‐angle laser light scattering (LALLS) performed in pure NMP. Intrinsic viscosity and molecular weight data for a series of nine samples of one polyimide covering a Mw = 20,000–70,000 g mol–1 interval were treated to obtain Mark‐Houwink‐Sakurada constants. Unperturbed chain dimensions of this polyimide were obtained by application of the Stockmayer‐Fixman extrapolation procedure to these data. ©1995 John Wiley & Sons, Inc.
A nuclear magnetic resonance study of dynamics in toluene‐polyisobutylene solutions: 1. Penetrant diffusion and Fujita theory
Authors: Bandis Athinodoros , Inglefield Paul T. , Jones Alan A. , Wen Wen‐Yang 
Published: April 2003

AbstractThe self‐diffusion coefficients of toluene in polyisobutylene (PIB) solutions were determined using the pulsed field gradient nuclear magnetic resonance technique. The volume fraction of toluene in the polymer was varied from 0.045 up to 0.712 and the temperature was varied from 225 K up to 368 K. The concentration dependence of the data was interpreted using the Fujita free volume theory and the temperature dependence was interpreted with the WLF equation. These models describe separately the concentration and temperature dependencies of the toluene self‐diffusion coefficients very well and the resulting free volume parameters are in good agreement with the ones extracted from the analysis of viscosity data on the same system. ©1995 John Wiley & Sons, Inc.
Multiplet formation in calcium partially neutralized poly(acrylamidocaproic acid)
Authors: Kim Hee‐tak , Park Jung‐ki , Lee Kew‐ho 
Published: April 2003

AbstractThe multiplet formation in calcium partially neutralized poly(acrylamidocaproic acid) was studied by using differential scanning calorimetry and Fourier transform infrared spectroscopy. At 20 mol % of neutralization of acid groups, the ionic groups started to aggregate to form multiplets. The hydrogen bonding of amide group was destroyed during multiplet formation due to the reduction of the motional freedom of the side chain. The extension of the short side chain started to be loosened at the neutralization of 44 mol %. In this state, the multiplets could be formed without severe side chain stretching due to the proximity of the ionic groups. It is expected that the more stable multiplet is formed with increasing the degree of neutralization. © 1995 John Wiley & Sons, Inc.
Coagulation of poly(p‐phenylene benzobisoxazole) in polyphosphoric acid using aqueous and nonaqueous solutions
Authors: Gillie J. K. , Newsham M. D. , Sen A. , Bubeck R. A. 
Published: April 2003

AbstractDiffusion of aqueous and nonaqueous coagulants into lyotropic/nematic solutions of poly(phenylene benzobisoxazole) in polyphosphoric acid using fluorescence microscopy is reported. The fluorescence microscopy technique offers advantages in that the experiment is independent of the coagulant and the experiments can be performed in a front surface mode so that optically thin samples are not required. The diffusion process is modeled as Case II diffusion as described by Crank and Park. The apparent diffusion coefficients are found to range from ∼ 2 × 10−6cm2/s to ∼ 2 × 10−7cm2/s for aqueous and nonaqueous coagulants. The apparent diffusion coefficients can be varied by several orders of magnitude (e.g., down to ∼ 3 × 10−10cm2/s) by varying the concentration of polyphosphoric acid in the coagulant. © 1995 John Wiley & Sons, Inc.
Thermodynamic interaction parameters in polymer solutions and gels
Authors: Horkay Ferenc , Hecht Anne‐Marie , Geissler Erik 
Published: April 2003

AbstractPolymer‐solvent interaction parameters are reported for poly(vinyl acetate)‐acetone, poly(vinyl acetate)‐toluene, and poly(dimethyl siloxane)‐toluene systems using different techniques. Results obtained by osmotic deswelling are compared with those from quasi‐elastic light scattering and small‐angle neutron scattering (SANS). In gels, the latter techniques involve separation of the time‐dependent from the static component of the scattered radiation+ Separation is achieved in quasi‐elastic light scattering through the heterodyning properties of the light, and in SANS by subtracting an appropriate static structure factor. The interaction parameters obtained by different separation procedures are consistent with measurements using the osmotic method. © 1995 John Wiley & Sons, Inc.
Dynamic mechanical properties of ionomer/ionomeric microbead composites
Authors: Cousin P. , Smith P. 
Published: April 2003

AbstractComposites of sulfonated polystyrene (PS‐SSA) (0‐8 mol % sulfonation) mixed with submicronic styrene‐4 vinylpyridine (PS‐4VP) (31 mol % 4VP content) microspheres were investigated by differential scanning calorimetry, Fourier transform infrared spectroscopy, and dynamic mechanical spectroscopy at 1 Hz in the glass transition region. The resulting proton transfer reaction from the SSA to the 4VP units was confirmed by IR spectroscopy, and led to a significant increase in the post‐Tg Young's modulus as well as a lengthening of the rubbery plateau. Surprisingly, the addition of sulfonated polystyrene microspheres to styrene‐vinyl pyridine copolymers had no such effects, possibly because of steric factors. © 1995 John Wiley & Sons, Inc.