bluuebunny/crossref_metadata_2025_split huggingface dataset:
Free volume in glassy poly(arylene ether ketone)s
Authors: Hinkley J. A. , Eftekhari A. , Crook R. A. , Jensen B. J. , Singh J. J. 
Published: April 2003

AbstractAmorphous polyarylene ether ketones were examined in the glassy state by positron annihilation lifetime spectroscopy (PALS) and in the melt by standard rheological techniques. Specimens were well‐characterized fractions of two isomeric structures. PALS clearly shows that the polymer with meta linkages in its backbone contains larger voids (> 0.25 nm radius). Thus despite their similar bulk densities, the two materials must pack very differently on a local scale. On the other hand, the free volumes inferred from the WLF treatment of melt viscosity data are practically identical in both materials ca. 4% at Tg. The comparison between techniques sheds some light on the distribution of free volume. © 1992 John Wiley & Sons, Inc.
Bulk and microscopic properties of copolymer networks in mixed aqueous solvents
Authors: Varelas C. G. , Steiner C. A. 
Published: April 2003

AbstractAmphiphilic films and hydrogels have been prepared from ethanol/water solutions containing a hydrocarbon‐grafted water‐soluble cellulose ether. These materials are characterized by dispersed hydrophobic microdomains which form spontaneously in the solvent due to the inherent incompatibility of the side chains with water. At low applied shear stress, the microdomains behave as temporary linkages of finite lifetimes, imparting viscoelastic properties to the networks. The molecular weight between microdomains was found to be independent of the volume fraction of polymer in the gel, and the number of linkages per backbone ranges from 22.8 ± 1.3 to 26.2 ± 1.5 over the frequency range 30–50 rad/s. The behavior of the solutions and gels was characterized using fluorescence and dynamic rheological measurements. It was demonstrated that the microdomains are capable of sequestering water‐insoluble solutes. © 1992 John Wiley & Sons, Inc.
Morphology of Nylon‐6 blends with styrenic polymers
Authors: Takeda Y. , Paul D. R. 
Published: April 2003

AbstractThe morphology of blends of styrenic polymers in a matrix of 75% Nylon‐6 prepared in a Brabender Plasti‐Corder was examined by scanning electron microscopy. Styrene/acrylonitrile copolymers (SAN) form smaller particles as the AN level increases owing to the corresponding decrease in the SAN–polyamide interfacial tension. Various styrenic polymers containing functional groups, maleic anhydride or oxazoline type, that can react with Nylon‐6 during melt processing were added to the SAN phase which also led to a decrease in the particle size owing to the graft copolymer formed in situ. The effects of functional group type, amount of functional groups per chain, amount of functional polymer added, and the miscibility of the styrene/maleic anhydride (SMA) and SAN copolymers on the morphology of the styrenic phase in the Nylon‐6 matrix are described. © 1992 John Wiley & Sons, Inc.
Dynamic light scattering from bulk poly(n‐hexylmethacrylate) near and above the glass transition
Authors: Giebel L. , Meier G. , Fytas G. , Fischer E. W. 
Published: April 2003

AbstractPhoton correlation spectra of polarized scattered light from poly(n‐hexylmethacrylate) PHMA (Mw = 1.6·105, Tg = −5°C) have been studied in the temperature range of −2–25°C. The experimental time correlation functions over the time range 10−6−102 s were represented by the Kohlrausch‐Williams‐Watts (KWW) function exp{−(t/τ)β} with a virtually temperature‐independent distribution parameter β = 0.27 ± 0.02. The observed relaxation functions were also analyzed in terms of a continuous distribution of retardation times L(τ) by means of a direct inverse Laplace transformation. The computed L(τ) distributions reveal a broad single peak structure in agreement with the results of the single KWW fit. The temperature dependence of τ is very similar to that of the shift factors obtained from measurements of the shear modulus and the stress relaxation modulus in the glass‐rubber region. Conversely, the values of τ compare well with those extracted from the experimental dielectric loss peaks consistently represented in the time domain by the KWW function. These findings suggest that the slow density fluctuations in bulk PHMA are associated with the primary glass‐rubber or α‐relaxation, which, however, displays an unusual low apparent Arrhenius activation energy and a rather low β value. PHMA exhibits significant dynamic light scattering with correlation times faster than 10−6 s near Tg. © 1992 John Wiley & Sons, Inc.
Thermoreversible gels of polyacrylonitrile
Authors: Bashir Z. 
Published: April 2003

AbstractPolyacrylonitrile (PAN) is soluble at room temperature in some ionic aqueous media and in many polar organic liquids such as dimethyl sulfoxide, but the polymer will not crystallize from these solvents. It is known, however, that PAN will from single crystals from dilute propylene carbonate (PC) solutions. It was found that on cooling concentrated PAN‐PC solutions, thermoreversible gels were formed. The gels showed x‐ray diffraction peaks and calorimetry indicated first‐order dissolution endotherms and crystallization exotherms. Thus, on cooling, crystallization of the polymer from this solvent was identified as the cause for gelation of concentrated solutions. © 1992 John Wiley & Sons, Inc.
Analysis of polymer films by diffuse reflectance FTIR spectroscopy: Characterization of terminal carboxyl functionalities
Authors: de Donato P. , Cases J. M. , Humbert B. , Lutgen P. , Feyder G. 
Published: April 2003

AbstractFourier transform infrared (FTIR) spectroscopy in the diffuse reflectance mode was used to study polyethylene terephthalate (PET) films. The polymer film (12 μm, molecular weight M1 = 18,000) was placed on a finely powdered KBr matrix, used as a reference. Infrared spectra exhibited a new band at 1684 cm−1, not usually reported in the literature. This band is assigned to the CO stretching vibration of a terminal acidic function in the presence of internal hydrogen bonds. In the carbonyl region, artifacts created by specular reflection are also discussed. The assignment of the band at 1684 cm−1 is confirmed by transmission measurements on the overtone of carbonyl group (3335 cm−1), using polymer films with thicknesses greater than 200 μm and by comparison with polymer of different molecular weight. These acidic functions can be used to monitor the rate of polymerization. It is therefore possible to obtain information on the polymerization rate of PET films, using diffuse reflectance and transmission analysis, directly on the solid. © 1992 John Wiley & Sons, Inc.
Flow birefringence studies of a concentrated polystyrene solution in a two‐roll mill. I. Steady flow and start‐up of steady flow
Authors: Geffroy Enrique , Leal L. Gary 
Published: April 2003

AbstractWe have studied a 4.8 volume percent solution of a narrow distribution polystyrene with molecular weight 3.84 × 106 in flows generated by a co‐rotating two‐roll mill. These flows have a stagnation point at the midpoint between the roller axes. Further, they are linear, two‐dimensional, and the magnitudes of the strain‐rates are greater than the vorticity. The overall objective of our studies is to explore the dynamics of concentrated polymer solutions which are in the highly deformed state that is generated in the two‐roll mill. Birefringence data are presented for both steady flow and start‐up of steady flow in the two‐roll mill. The steady and transient data are used to analyze the linear and nonlinear viscoelastic regions of material behavior. In the nonlinear regime, the birefringence upon start‐up shows an initial overshoot followed by a strong undershoot that is enhanced as the ratio of elongation to rotation is increased (i.e., the flow becomes increasingly extensional in character.) We attribute this undershoot, which does not seem to appear in simple shear flows, or flows close to simple shear flow, to polymer segment stretching following an initial period of segment reorientation. Model studies are currently underway to test this notion. © 1992 John Wiley & Sons, Inc.
Prediction of miscibility regions in ternary blends of poly(styrene‐stat‐acrylonitrile), poly(acrylonitrile‐stat‐methyl methacrylate), and poly(styrene‐stat‐methyl methacrylate)
Authors: Cowie J. M. G. , Li Guangxian , Ferguson R. , McEwen I. J. 
Published: April 2003

AbstractThe miscibilities of ternary copolymer blends prepared from poly(styrene‐stat‐acrylonitrile), poly(styrene‐stat‐methyl methacrylate), and poly(methyl methacrylate‐stat‐acrylonitrile) were predicted by calculating the interaction parameter, χblend, for various blend combinations, from the corresponding binary segmental interaction parameters estimated from previous work. Binodal and spinodal curves were calculated using the Flory‐Huggins theory and it was observed that the most accurate estimate of the boundary between miscible and immiscible blends was given by the spinodal. It has also been demonstrated that in some of the ternary blends with fixed copolymer compositions the miscibility of the blend can be altered by changing the ratio of the three components in the mixture. Conditions for miscibility in this ternary system, and possibly a general feature of all such systems, are (a) that at least two of the binary interaction parameters χij are less than the critical value χcrit, while the third should not be too much larger, that is, one of the copolymers may act as a compatibilizer for the other two copolymers, (b) that the difference Δχ = /χ12 − χ13/ is small. © 1992 John Wiley & Sons, Inc.
Direct measurement of free‐volume hole distributions in polymers by using a positronium probe
Authors: Jean Y. C. , Deng Q. 
Published: April 2003

AbstractWe have directly measured the free‐volume hole distributions in semicrystalline polypropylene by positron lifetime annihilation spectroscopy. A Laplace inversion technique was engaged to analyze the positron lifetime spectra measured under quasi‐isotropic external pressures of 0, 4.2, and 14.7 kbar into continuous lifetime distributions. The hole radii distributions as determined from the ortho‐positronium lifetime distributions are found to be between 4.0 and 0.5 Å and to have maxima at 3.0, 1.9, and 1.1 Å under the external pressures of 0, 4.2, and 14.7 kbar, respectively. © 1992 John Wiley & Sons, Inc.
Temperature and stress effects in the creep of aramid fibers under transient moisture conditions and discussions on the mechanisms
Authors: Wang John Z. , Dillard D. A. , Ward T. C. 
Published: April 2003

AbstractIn a previous study, a mechanosorptive phenomenon in poly(p‐phenylene terephthalamide) fibers was reported. In this article, the mechanosorptive creep mechanism of aramid fibers and the temperature and stress influences on the mechanosorptive creep behavior of aramid fibers are addressed. Test results indicate that logarithmic creep rates and the mechanosorptive effects increase with temperature. The creep activation energies of the fibers tested are: 20 kJ/mole for the cyclic moisture condition, 4.4 kJ/mole for a high equilibrium moisture condition (RH = 95%), and 7.8 kJ/mole for a low equilibrium moisture condition (RH = 5%). Increase in stress may increase the logarithmic creep rates but may reduce the mechanosorptive effect. Aramid fibers contain hydrogen bonds between rodlike crystallites oriented at small angles relative to the fiber axis. Transient moisture conditions may cause slippage of hydrogen bonded elements and result in accelerated crystallite rotations due to breakage of hydrogen bonds, thus causing increases in logarithmic creep rate. The obtained activation energies and the reduction in fiber elastic compliance due to creep deformation support the proposed mechanisms. © 1992 John Wiley & Sons, Inc.
Thermal elimination of isobutene from meta and para tert‐di‐butyl pyromellitic acid
Authors: Johnson C. , Xu Huizhu , Wunder S. L. , Houlihan F. M. , Chin E. 
Published: April 2003

AbstractAn investigation of the kinetics of the thermal elimination of isobutene from the meta and para isomers of the tert‐butyl diesters of pyromellitic acid has been carried out using Fourier transform‐Raman spectroscopy and mass spectroscopy. These studies indicate that the elimination of the tert‐butyl group occurs at a temperature 26°C lower for the meta isomer than for the para isomer; the maximum rate of elimination occurs at 184°C for the former and at 210°C for the latter. Analysis of the Raman spectra of the compounds indicates that this effect results from the better packing arrangement in the para monomer compared with the meta monomer. Formation of pyromellitic dianhydride in the tert‐butyl diesters of pyromellitic acid occurred only after formation of the pyromellitic acid; thus it occurred at lower temperatures for the meta isomer. When the meta and para tert‐butyl diesters of pyromellitic acid are dissolved at 1% concentration in poly (vinyl acetate), the elimination of isobutene occurs at 173°C for both isomers, indicating that it is the differences in crystal packing which give rise to the 26°C difference in the solid‐state samples. For the meta, para, and 50/50 mixed isomers of the tert‐butyl esters of oxydianiline/pyromellitic dianhydride polyamic acid, the elimination of the tert‐butyl group occurs at the same temperature (177°C). This result indicates that the packing arrangement of the tert‐butyl group is disrupted in the polymer chain, so that intermolecular bonding does not hinder thermal deprotection of the tert‐butyl group from the polymer. © 1992 John Wiley & Sons, Inc.
Diffusion of camphorquinone in uniaxially drawn polycarbonate films
Authors: Xia J. L. , Wang C. H. 
Published: April 2003

AbstractEmploying the laser‐induced holographic grating relaxation technique, we have measured tracer diffusion coefficients of a phtochromous dye, camphorquinone, in uniaxially drawn polycarbonate films as a function of stretch ratio. Anisotropy in the tracer diffusion coefficient has been observed with D∥ greater than D⟂ by at least a factor of 4 for the film stretched to the stretch ratio δ = 2.3. The diffusion coefficient along the direction of stretch D∥ increases significantly with increasing δ, whereas D⟂ decreases slightly with increasing δ. The stretch ratio dependence of D∥ and D⟂ is interpreted according to a modified free volume theory. The strain rate and stretch temperature dependence of the anisotropic tracer diffusion coefficient has also been investigated. © 1992 John Wiley & Sons, Inc.
Dielectric properties of a PMMA/E7 polymer‐dispersed liquid crystal
Authors: Zhong Z. Z. , Schuele D. E. , Gordon W. L. , Adamic K. J. , Akins R. B. 
Published: April 2003

AbstractDielectric measurement on a polymer‐dispersed liquid crystal (PDLC) has been carried out in the frequency range from 10 Hz to 1 MHz and over the temperature range from 100 to 330 K. The PDLC sample was prepared by thermally induced phase separation of a 50% mixture by weight of commercially available liquid crystal E7 with PMMA and was sandwiched between two indium tin oxide glass plates separated by 40 μm spacers to form a “window.” The dielectric spectrum at low temperature (220–250 K) shows two distinct relaxation processes. Which occur at about 5 K lower than those in pure E7 having Tg ≈ 209 K. From differential scanning calorimetry data, the nematic transition of LC droplets in the PDLC is at 258 K, about 6 K lower than that of pure E7. The Maxwell‐Wagner effect has been observed in the low‐frequency side as the temperature increases from 280 to 320 K. At room temperature, the loss peak associated with the Maxwell‐Wagner effect shows an amplitude dependence with excitation level but no frequency shift. The effect of different concentrations of E7 in PDLC samples at a given temperature shows the 50% mixture has the “fastest” relaxation frequency in such a dispersed heterogeneous system. © 1992 John Wiley & Sons, Inc.
Lamellar and whisker single crystals of poly(2,6‐oxynaphthoate)
Authors: Liu J. , Rybnikar F. , Geil P. H. 
Published: April 2003

AbstractElectron diffraction from single crystal lamellae and whiskers of poly(2,6‐oxynaphthoate) reveals the presence of at least 3 unit cells. The equatorial reflections in the patterns from the whiskers correspond to the dominant (phase I) hk0 diffraction pattern from the lamellae; phase I is monoclinic with 2 chemical repeats per physical repeat. The intensity distributions in the hk0 patterns of phase I and II resemble those of the same phases in poly(p‐oxybenzoate). The hk0 reflections of phase III suggest a common internapthalene unit spacing, but variable lateral (and possibly axial) shifts; apparently related orthorhombic and monoclinic patterns, with variable γ*, are observed. At elevated temperature, above the crystalliquid crystal transition (ca. 330°C), quadrant reflections are retained; the change in the hk0 pattern from any given crystal is gradual, extending over some 40°C. Above the liquid crystal‐liquid crystal transition (ca. 460°C) the pattern can be interpreted in terms of nematic or possibly smectic A packing. © 1992 John Wiley & Sons, Inc.
Optical anisotropy of polymeric films measured by waveguide propagation mode determination
Authors: Bai S. J. , Spry R. J. , Zelmon D. E. , Ramabadran U. , Jackson J. 
Published: April 2003

AbstractExtruded thin films of a liquid‐crystalline charge‐conjugated rigid‐rod polymer poly(p‐phenylenebenzobisthiazole), PBT, and a semicrystalline thermoplastic polyethylene‐terephthalate (Mylar) were fabricated and examined for film thickness, refractive index, and linear attenuation coefficient. Optical waveguide modes were successfully induced on the polymeric films using a prism coupler at λ = 633 and 1300 nm. Highly consistent thickness values were obtained for the polymeric films. In addition, the anisotropic nature of the optical properties was determined using TE and TM propagation modes. A refractive index as high as 2.3 was observed on PBT film. The refractive index data suggested that the PBT and Mylar films were optically anisotropic with refractive indices n⟂ (out‐of‐plane) invariably smaller than n∥ (in‐plane). Large anisotropy was also discovered in the linear attenuation coefficient α, with α∥/α⟂ ≈ 50 for the Mylar films. Complementary polarimetric and spectroscopic interference measurements were also applied to investigate the optical anisotropy of the extruded polymeric films. © 1992 John Wiley & Sons, Inc.
Bulk rigid‐rod molecular composites of articulated rod copolymers with thermoplastic pendants
Authors: Bai S. J. , Dotrong M. , Evers R. C. 
Published: April 2003

AbstractBulk rigid‐rod molecular composites were successfully obtained by powder consolidation of a copolymer containing both the reinforcing rigid‐rod segments and the thermoplastic matrix. By chemically linking the reinforcing segments and the matrix molecule, the copolymer was designed to minimize phase separation in the molecular composite. The copolymer was an articulated rigid‐rod poly(p‐phenylenebenzobisthiazole), aPBT, with an aromatic poly(ether ketone), mPEK, thermoplastic pendant grafted at the points of articulation. The copolymer powder was pre‐formed and compression molded at an elevated temperature, which resulted in bulk rigid‐rod molecular composites with three‐dimensionally isotropic properties. Compared to the neat mPEK homopolymer, significant increases in glass transition temperature Tg and tensile properties have been realized for the aPBT‐g(mPEK) copolymers with low rod content. Taking into account the aspect ratio of the aPBT, the bulk rigid‐rod molecular composite showed a tensile modulus as predicted by the Halpin‐Tsai equation. In addition, x‐ray scattering revealed minimal rod aggregation. However, for the copolymer of higher rod content, significant phase separation was observed in the copolymer powder, which resulted in a decrease in Tg as well as reinforcement efficiency of the bulk rigid‐rod molecular composite as compared to those derived from the copolymers of low rod content. © 1992 John Wiley & Sons, Inc.
Extension of miyazawa's equations to the case of an arbitrary number of junction atoms in a molecular helix
Authors: Kandakov A. V. , Ginzburg B. M. 
Published: April 2003

AbstractAn algorithm is proposed for the construction of Miyazawa's equations with an arbitrary number of junction atoms in the repeat unit of the macromolecule. In these equations the helical parameters of an infinite polymer chain and the internal parameters of the chain, bond lengths, bond angles, and internal rotation angles, are interrelated. © 1993 John Wiley & Sons, Inc.
Study of crystalline orientation in drawn ultra‐high–molecular weight polyethylene films
Authors: Lafrance Claude‐Paul , Debigaré Josée , Prud'homme Robert E. 
Published: April 2003

AbstractA wide‐angle x‐ray diffraction (WAXD) study of the development of molecular orientation in the crystalline phase of ultra‐high–molecular weight polyethylene films prepared by the gelation–crystallization method is presented. WAXD scans of the undrawn films show that the lamellae are oriented in the plane of the films. Upon drawing at 130°C, the orientation of the molecular chains changes from the direction normal to the film surface (ND) to the elongation direction. The decrease of the 200/020 intensity ratio at low draw ration (λ <10) indicates that double orientation develops during the transformation from the lamellar to the fibrillar morphology, with the a‐axis oriented parallel to ND. The orientation distributions of the 110, 200, 020, and 002 planes of the orthorhombic unit cell of polyethylene were studied and characterized by the coefficients of a Legendre polynomial series. At a draw ratio of 4.5, the second‐order coefficient, 〈P2(cos χ〉, already gets close to its limiting value, but it is shown that higher order coefficients of the polynomial series can be used to describe the evolution of the orentation, even up to λ = 50. The coefficients relative to the molecular chain orientation, 〈Pn(cos χ)〉c, can be calculated from different crystalline reflections. Curve‐fitting calculations were made in order to improve the correlation between the results obtained from the orientation distribution of the 110, 020, and 002 planes. A Person VII function was found to give a better fit of the experimental curves than Gaussian or Lorentzian equations. © 1993 John Wiley & Sons, Inc.
The effect of increased crystallization on the electrical properties of nylon‐12
Authors: Pathmanathan K. , Johari G. P. 
Published: April 2003

AbstractThe dielectric properties of 30% crystalline dry Nylon‐12 have been measured over the frequency range 10–105 Hz and temperature range 300–450 K, and the effect of its annealing at 423 K investigated both by dielectric measurement and differential scanning calorimetry. Annealing causes its crystallization to α phase, which increase the dc conductivity and decreases the contribution to orientation polarization, but does not alter the shape of the relaxation spectrum. The orientation polarization in Nylon‐12 involves two processes, each of which occurs above the glass‐transition temperature of Nylon‐12, but only the spectra of the lowest temperature process could be clearly resolved. © 1993 John Wiley & Sons, Inc.