bluuebunny/crossref_metadata_2025_split huggingface dataset:
Structural investigations of polymer liquid‐crystalline solutions: Aromatic polyamides, hydroxy propyl cellulose, and poly(γ‐benzyl‐L‐glutamate)
Authors: Onogi Yoshihiko , White James L. , Fellers John F. 
Published: April 2003

AbstractA comparative structural investigation of the characteristics of polymer liquid‐crystalline solutions including Kevlar® (PPD‐T)/sulfuric acid, poly(Cl‐p‐phenylene terephthalamide) (Cl‐PPD‐T)/sulfuric acid, poly(γ‐benzyl‐L‐glutamate) (PγBLG)/dioxane, and hydroxypropyl cellulose (HPC)/water was undertaken. Experimental procedures included polarized light microscopy, light scattering, absorption spectra, and x‐ray diffraction on solutions at various concentrations and temperatures. Both the two‐phase region at the onset of liquid‐crystal formation and the wholly anisotropic phase were investigated. Each solution exhibited distinctive characteristics. The PPD‐T and Cl‐PPD‐T solutions were nematic, and the PγBLG and HPC solutions were cholesteric. In the two‐phase region the PPD‐T, Cl‐PPD‐T, and PγBLG (but apparently not the HPC) exhibited negatively birefringent spherulites and aggregates of spherulites. The HPC solutions only exhibited spherulitic structures in the single‐phase anisotropic system. The structures and orientations in the anisotropic phase for the various polymer solutions is considered. The helicoidal structural characteristics of the PγBLG and HPC solutions are contrasted.
Crystal structure of polyamides containing 1,3‐cyclohexane rings
Authors: Inoue Kazuo , Hoshino Sadao 
Published: April 2003

AbstractThe effect of 1,3‐cyclohexane rings in the chain backbone on the crystal structure of polyamides has been studied using polyamides (denoted 1,3‐CBMA‐n) obtained from 1,3‐cyclohexane‐bis(methylamine) (1,3‐CBMA) and n‐carbon dicarboxylic acids. The crystallinity of the 1,3‐CBMA‐n polymers changes greatly with variation in the value of n. This is attributed to hydrogen‐bond changes associated with the relative length of the diacid moiety to the diamine moiety in the monomeric unit of each polymer. In 1,3‐CBMA‐6, the cis‐1,3‐cyclohexane rings are readily accommodated in the molecular chains to form crystals in a manner similar to the m‐benzene rings in poly(m‐xylylene adipamide) (MXD‐6). The crystal lattice, however, is more expanded than in MXD‐6 since the 1,3‐cyclohexane rings is bulkier than the m‐benzene ring. The crystal structure of the 1,3‐CBMA‐n polymers is essentially the same as that of MXD‐6.
Effect of moisture on the bulk properties of salted poly(caproamide)
Authors: Acierno D. , La Mantia F. P. , Titomanlio G. , Ciferri A. 
Published: April 2003

AbstractThe glass‐transition temperature (Tg) and the elastic modulus of nylon‐6 and its mixtures with 4% w/w LiCl and with 2% LiCl+3% LiBr were investigated. In one set of experiments care was taken to avoid absorption of moisture during the measurements. In another set of experiments, samples were exposed to atmospheric humidity for different lengths of time. Both unoriented and oriented specimens were investigated. The presence of 4% LiCl almost doubles the amount of moisture absorbed at equilibrium by nylon‐6. The Tg was found to be greatly affected by the moisture content and by salt type. When strict precautions to exclude moisture are taken, the addition of 4% LiCl raises the Tg of nylon‐6 by about 25°C. The elastic modulus of oriented samples is increased by the addition of salts provided moisture is completely absent. This beneficial effect is, however, completely eliminated when samples are allowed to equilibrate with atmospheric moisture.
Morphology and tensile property relations of high‐strength/high‐modulus polyethylene fiber
Authors: Wu W. , Simpson P. G. , Black W. B. 
Published: April 2003

AbstractHigh‐strength/high‐modulus polyethylene (PE) fibers have been obtained from linear polymers by melt‐spinning the polyethylene followed by hot‐drawing the spun filaments. Fibers with different tensile properties were made by changing the extrusion, solidification, and drawing conditions and by use of different types of polyethylene. Potential correlations of fiber strength with morphological parameters such as crystallite dimensions, and crystalline and amorphous orientation were examined. The integrated meridional small‐angle x‐ray scattering intensity is the only morphological parameter which was found to correlate well with the strength of fibers prepared under different conditions and from different polymer types. Implications with respect to the molecular mechanism of PE fiber drawing are also discussed.
Physical and rheological characterization of poly(aryloxyphosphazene) copolymers
Authors: Futamura S. , Valaitis J. K. , Lucas K. R. , Fieldhouse J. W. , Cheng T. C. , Tate D. P. 
Published: April 2003

AbstractA series of poly(aryloxyphosphazene)s was prepared with phenoxy and p‐ethylphenoxy substituents in various ratios. The thermal, morphological, and rheological properties of this series of polymers were studied by differential thermal analysis, x‐ray analysis, and rheometrics mechanical spectroscopy. Thermal analysis showed that the resulting polymers follow melting‐point‐depression‐ and glass‐transition‐temperature‐composition relationships expected of random copolymers. The lower first‐order transition temperature [T(1)] disappears near equimolar substitution while the higher first‐order transition temperature (Tm) persists over the whole range of compositions. X‐ray analysis revealed that crystalline order in the polymer chain direction is destroyed by nearly equimolar substitution but lateral order remains. The rheological characterization of a copolymer with nearly equimolar substitution showed that the polymer is in a pseudocrosslinked state indicating the existence of chain‐to‐chain interactions. When a small amount of an antioxidant (6‐dodecyl‐1,2‐dihydro‐2,2,4‐trimethylquinoline) is added, the lateral order of the copolymer is destroyed, and its rubbery plateau modulus decreases by several fold.
Intrinsic viscosity of flexible ring polymers
Authors: Alessandrini J. L. 
Published: April 2003

AbstractThe intrinsic viscosity of flexible ring polymers with a finite number of segments is computed with both exact and approximate eigenvalues λk, in the frame of the elastic necklace model. It is shown that exact and approximate calculations of the Flory constant and the Kuhn‐Mark‐Houwink exponent of the non‐free‐draining limit are compatible with h* ⋍ 0.25 and N ≥ 100.
Measurement of single chain neutron scattering in concentrated polymer solutions
Authors: Akcasu A. Z. , Summerfield G. C. , Jahshan S. N. , Han Charles C. , Kim Chung Yup , Yu Hyuk 
Published: April 2003

AbstractFor some time there have been measurements of single‐chain form factors for small‐angle neutron scattering (SANS) in bulk polymers and in concentrated solutions. These were done by mixing a fraction of completely deuterated polymer with the normal polymer. Until recently, it was believed that these experiments had to be performed using a small fraction of deuterated polymer to avoid interchain interference effects. However, the work of Williams et al. has shown that these experiments are better if one uses large fractions of marked polymer and determines both the single chain and interference contributions to the SANS cross section. We generalize the technique of Williams et al. somewhat and apply it to the measurement of the radius of gyration of polyisoprene in the bulk.
Observation of bands in high‐modulus aramid fibers by polarization microscopy
Authors: Simmens S. C. , Hearle J. W. S. 
Published: April 2003

AbstractExamination of the highly oriented aramid fiber, Kevlar, at high magnification in an optical microscope in the extinction position between crossed polars gives an image with regions of regular fine bands. The diffraction pattern shows first order but no zero order. This is interpreted as being due to the passage of depolarized scattered light from a material with regularly spaced discontinuities. This is identified with the pleated structure proposed by Dobb et al.
Model for sorption of mixed gases in glassy polymers
Authors: Koros W. J. 
Published: April 2003

AbstractA model is presented for analysis of the sorption of mixed gases in glassy polymers at concentrations below which significant plasticization occurs. The well‐known dual‐mode sorption model comprised of a Henry's law term and a Langmuir isotherm term, which has been used extensively for interpretation of single‐component gas sorption data, forms the basis for the analysis of binary mixtures discussed here. Measurements using pure gases provide dual mode parameters which can then be used to predict the resultant sorption isotherms for binary mixtures of any of the pure gases. The proposed analysis is based upon recognition that the Langmuir component of the overall sorption concentration should be governed by competition between the two penetrants for the fixed unrelaxed volume in the polymer, which is believed to be the locus of the Langmuir capacity. This effect may result in a significant depression of the measured sorption of similar penetrants competing for the limited Langmuir capacity. A numerical example is considered which illustrates the range of behavior expected for CO2 and CH4 in polycarbonate. Deviations from the theoretical predictions of the simple dual‐mode model for binary systems are discussed in terms of plasticizing effects on the Henry's law constant and the Langmuir affinity constant. The analyses proposed here are of direct and critical interest to the applied problems of migration of trace contaminants in glassy polymers and analysis of barrier packaging for foods since all of these applied problems involve mixed‐penetrant sorption. Specifically, it is predicted that the presence of residual monomers or solvents in glassy polymers can produce both anomolously low Langmuir sorption affinity constants and sorption enthalpies compared with the residual‐free case.
Structure of glassy polymers. VII. Small‐angle X‐ray scattering from epoxy resins
Authors: Matyi R. J. , Uhlmann D. R. , Koutsky J. A. 
Published: April 2003

AbstractThe small‐angle x‐ray scattering (SAXS) from an Epon 812 and two Epon 828 (one amine‐cured and one anhydride‐cured) epoxy resins has been measured using a Bonse‐Hart system. The data cover the angular range (2θ) between 20 sec and 60 min. After correction for absorption, background and vertical beam divergence, they have been placed on an absolute basis by comparison with the scattering from a previously studied polycarbonate sample. The corrected absolute intensity decreases strongly with increasing angle between 20 sec and 2 min, decreases more gradually between 2 and 20–30 min, and reaches a nearly constant asymptotic value at larger angles. The magnitude of the intensity in the constant‐intensity region is close to the value predicted by thermodynamic fluctuation theory for fluids applied at the glass transition temperature. The increase in intensity at angles smaller than 20–30 min is associated with heterogeneities in the cured resins. These heterogeneities cover a range of sizes in all samples, from less than 100 Å to more than 1000 Å, with the most frequently occurring size in the range 100–200 Å.
Crystal orientation relaxation studies of polyethylene
Authors: Cembrola Robert J. , Stein Richard S. 
Published: April 2003

AbstractWide‐angle x‐ray relaxation studies were performed on films of low‐ and high‐density polyethylene (PE). The samples were rapidly stretched by a pneumatic stretcher and held at a fixed length. The rate of crystal reorientation was monitored by measuring diffracted intensity changes using a count‐rate meter with output displayed on a storage oscilloscope as well as a digital counter‐timer. Experiments were completed at several temperatures and activation energies comparable to those reported for the α1 relaxation in PE were obtained.
Kinetics of the II‐III phase transformation of polytetrafluoroethylene at high pressure
Authors: Nicol Malcolm F. , Wiget Joseph M. , Wu C. K. 
Published: April 2003

AbstractThe rate of transformation from helical to all‐trans‐planar polytetrafluoroethylene (PTFE) at high pressures has been determined by monitoring the Raman spectra of PTFE following pressure jumps from the stability field of PTFE II to pressures between 9 and 14 kbar at temperatures between 0 and −30°C. The transformation kinetics can be described by Avrami's equation for nucleation and growth kinetics with an exponent of 0.5, although observations at lower temperatures suggest that even smaller values of the exponent may be appropriate. At 10 kbar and 0°C, the specific rate constant is 0.51 min−1/2. The energy and volume of activation are 11 kcal mole−1 and −7 cm3 mole−1, respectively. The values of these parameters suggest that the transformation mechanism involves propagation of helix reversal planes along the several adjacent chains leaving all‐trans material in their wakes.
Distribution of chain defects and microstructures of melt crystallized polyethylene. II. Influence of defect size and of plastic deformation
Authors: Baltá‐Calleja F. J. , Hosemann R. 
Published: April 2003

AbstractUnit cell expansion data for (a) melt‐crystallized polyethylene (PE) containing known amounts of methyl, ethyl, and butyl branches and for (b) plastically deformed samples, are examined in the light of a model which takes into account the penetration of constitutional defects (branches) at interstitial crystal sites by means of a generation of 2g1 step chain defects (kink isomers). The present analysis complements previous results obtained for melt‐crystallized PE samples with a widely varying number concentration ϵ of butyl or longer branches. An estimation of the concentration of chain defects incorporated into the crystal lattice is carried out. The results reveal that the fraction χc of defects which are accomodated within the lattice depends on both the amount and size of the chain defects and on the mechanical deformation of the sample. For PE chains with methyl and ethyl groups, χc ≈ 50%, whereas for butyl and longer branches, χc does not exceed 20% of the total concentration of defects. In addition, after cold drawing, PE with low amounts (ϵ < 1%) of butyl or longer chain branching, χc turns out to be zero; i.e., during deformation single molecular chain rearrangements leading to a chain segregation of defects into the amorphous phase must occur.
Dependence of the conformational parameters of polyimides on the chemical structure of the chain
Authors: Pavlova S.‐S. A. , Timofeeva G. I. , Ronova I. A. 
Published: April 2003

AbstractThe flexibility of some polyimide chains has been studied theoretically as a function of the chemical structure of the repeat unit. It has been shown that the thermodynamic flexibility can be varied over a wide range by the choice of the unit structure. For three polyimides, as an example, the flexibility of cyclochain structures approximates that for free rotation.
Thermal conductivity of oriented crystalline polymers
Authors: Choy C. L. , Chen F. C. , Luk W. H. 
Published: April 2003

AbstractThermal conductivities of six oriented semicrystalline polymers which range from 0.37 to 0.63 in crystallinity and 1 to 5 in draw ratio λ (up to about 15 for two polymers) have been measured between 100 and 340 K. It was found that for increasing λ the conductivity K∥ (along the draw direction n̂) increases rapidly while K⊥ (normal to n̂) decreases slightly; K∥ also increases with temperature, but K⊥ shows no simple pattern in temperature dependence. These general features can be reproduced reasonably well at low draw ratio (λ < 5) by the modified Maxwell model, and the discrepancy in details may be attributed to the fact that the model does not take into account the possible anisotropy of the amorphous phase of the oriented polymers. At high draw ratio the intercrystalline bridge effect becomes important, and one must resort to the Takayanagi model, but the lack of corroborating x‐ray data has rendered a detailed comparison impossible.
Single crystals of cellulose IVII: Preparation and properties
Authors: Buleon A. , Chanzy H. 
Published: April 2003

AbstractLamellar single crystals of cellulose were obtained from dilute solutions of low‐DP cellulose triacetate, by deacetylation followed by precipitation. At temperatures between 150 and 160°C, pure cellulose IVII crystals were obtained whereas at temperatures between 90 and 150°C, hybrid crystals, having cellulose II and cellulose IVII domains cocrystallized in syntaxy were obtained. In both cases, the crystals were identified and characterized by electron diffraction. When the solutions leading to cellulose IVII were seeded with native cellulose microfibrils, a shish‐kebab structure resulted with the microfibrils decorated by cellulose II lamellae.
Polymer diffusion at intermediate concentrations
Authors: Chitrangad B. , Osmers H. R. 
Published: April 2003

AbstractSchlieren optics in conjunction with a modified Claesson cell allows free‐diffusion experiments to be performed over a wide range of polymer concentrations. A data analysis procedure is presented for computation of the mutual diffusion coefficient using this technique. The dependence of the diffusion coefficient on concentration in polymer solutions is satisfactorily explained in terms of free volume, and a relation is proposed for correlating the mutual diffusion coefficient and zero‐shear viscosity.
High‐temperature morphological transition in a styrene‐butadiene‐styrene block copolymer
Authors: Chung C. I. , Griesbach H. L. , Young L. 
Published: April 2003

AbstractElectron microscopy reveals a high‐temperature morphological transition in a styrene‐butadiene‐styrene block copolymer of 7000 polystyrene block molecular weight and 43,000 polybutadiene block molecular weight (7S‐43B‐7S). Samples quenched in liquid nitrogen from temperatures above 150°C show no structure, whereas those quenched from temperatures below 140°C clearly show a multiphase structure. We previously reported that the 7S‐43B‐7S polymer exhibits a relatively sharp melt rheological transition in the temperature region between 140 and 150°C from highly viscoelastic and nonlinear viscous behavior to linear viscous behavior with insignificant elasticity. The dynamic viscoelastic properties are measured at different strain amplitudes in this study, and the results show that the melt rheological transition behavior is not influenced by the strain amplitude. This study clearly shows that the melt rheological transition in the 7S‐43B‐7S results from a morphological transition from a multiphase structure below about 140°C to a single‐phase structure above about 150°C.
Morphology and melting behavior of semicrystalline poly(ethylene terephthalate). I. Isothermally crystallized PET
Authors: Groeninckx G. , Reynaers H. , Berghmans H. , Smets G. 
Published: April 2003

AbstractA detailed description of the morphology and the complex melting behavior of poly(ethylene terephthalate) crystallized isothermally in the range 100–245°C is presented. Double or single melting endotherms can deliberately be obtained by varying the heating rate in the differential scanning calorimeter (DSC). In the case of double melting peaks, the first endotherm (I) corresponds to the melting of the crystalline material formed at the crystallization temperature Tc. The second melting endotherm (II) originates from the melting of a fraction of the original crystalline material reorganized during the DSC scan. The appearance of one melting endotherm (I or II) relates to the melting of the original structure or the melting of a completely transformed structure. Taking the end of the melting endotherm I as the final melting temperature TM of the material, an equilibrium melting temperature of 290°C is obtained from a plot of TM vs. Tc. A detailed morphological study of the isothermally crystallized samples by electron microscopy and both small‐angle and wide‐angle x‐ray scattering raises questions about the use of the two‐phase concept in relating morphological parameters and melting behavior at low crystallization temperatures.
Direct evaluation of the electron density correlation function of partially crystalline polymers
Authors: Strobl G. R. , Schneider M. 
Published: April 2003

AbstractA discussion of the general properties of the one‐dimensional electron density correlation function K(z) of a partially crystalline polymer with lamellar structure shows that application of a graphical extrapolation procedure permits direct determination of the crystallinity, the specific inner surface, and the electron density difference ηc − ηa. The procedure is based upon the occurrence of a straight section in the “self‐correlation” range of K(z). Curved and nonparallel lamellae do not invalidate the concept. In the case of heterogeneous samples composed of partially crystalline and totally amorphous regions, some of the parameters of the experimentally obtained correlation function, as for example the invariant K(0), are affected and may lose their definiteness. Use of the method is demonstrated in a detailed discussion of the correlation functions measured for a sample of lowdensity polyethylene at 25 and 100°C.
Model of partial crystallization and melting derived from small‐angle X‐ray scattering and electron microscopic studies on low‐density polyethylene
Authors: Strobl G. R. , Schneider M. J. , Voigt‐Martin I. G. 
Published: April 2003

AbstractA temperature‐dependent small‐angle x‐ray scattering and electron microscopic study on a sample of low‐density polyethylene affords a determination of the structure changes in a heating and cooling cycle and suggests a new model of partial crystallization and melting. The analysis of SAXS data is based upon some general properties of the electron‐density correlation function. Electron micrographs are obtained from stained sections γ irradiated at elevated temperatures and are analyzed quantitatively by statistical means. According to the model proposed here the thickness distribution in the amorphous layers, rather than that of the crystalline regions, is the essential factor governing the crystallization and melting behavior. The temperature‐dependent changes in this thickness distribution provide a natural explanation for the large reversible changes in long‐spacing.
Thermochromism in polydiacetylene solutions
Authors: Patel G. N. , Witt J. D. , Khanna Y. P. 
Published: April 2003

AbstractA novel planar ↔ nonplanar visual thermochromic conformational transition of polydiacetylene molecules in poor solvents is reported. The conformational transition is associated with both a color change (blue or red ↔ yellow) and a change in the state; the yellow solution (liquid) transforms to a blue or red gel (solid). The color transition occurs within a narrow range of temperature and has a large associated hysteresis. The enthalpy of the conformational transition is 29 kJ/mole of repeat unit. Fourier‐transform infrared studies show that molecules acquire a planar conformation in red or blue gels by formation of intramolecular H bonds between the adjacent substituent groups. Virtually all H bonds break (a nonplanar conformation) when the gels turn into yellow solutions.