bluuebunny/crossref_metadata_2025_split huggingface dataset:
Gas sorption and transport in substituted polycarbonates
Authors: Muruganandam N. , Koros W. J. , Paul D. R. 
Published: April 2003

AbstractThe effects of molecular structure manipulation of polycarbonates on sorption and transport of various gases were studied using tetramethyl, tetrachloro, and tetrabromo substitutions onto the aromatic rings of bisphenol A polycarbonate. Solubility and permeability measurements were made at 35°C over the pressure range of 1–20 atm for a variety of gases, namely CO2, CH4, O2, N2, and He. A threefold to fourfold increase in permeability was caused by the tetramethyl substitution, whereas the tetrachloro and tetrabromo substitutions reduced the permeability relative to the tetramethyl substitution. Lower activation energies for transport were found for the tetramethyl polycarbonate relative to the unsubstituted polycarbonate. Permeability coefficients were factored into solubility and diffusion coefficients. Sorption levels increased for all substitutions, but among the substituted polymers the levels remain practically the same. Solubility data were analyzed in terms of the dual sorption model. The Henry's law solubility coefficients obtained from this analysis were found to be consistent with a predictive equation developed for rubbery polymers. The usual correlation for predicting the Langmuir sorption capacity of the model overestimates the values for the substituted polycarbonates, and a proposal for the cause of this is offered. Thermal expansion of these polymers was measured using dilatometry, and the results are used in the interpretation of the sorption data. Diffusion phenomena are explained by segmental mobility and free volume considerations. The effects of CO2 exposure history on sorption and transport were also investigated.
Effects of chain length distribution on viscoelastic properties of entangled linear polymers: Blending laws for binary blends
Authors: Kim Hee Young , Chung In Jae 
Published: April 2003

AbstractThe reptation idea of de Gennes and the tube model theory of Doi and Edwards are extended to explain the terminal viscoelastic properties of binary blends in the highly entangled state of two linear monodisperse polymers with different molecular weights M1 and M2. A modified tube model is proposed that considers the significance of the constraint release by local tube renewal in accounting for the relaxation process of the higher molecular weight chain. Its relaxation by both reptation and the constraint release is remodeled as the disengagement by pure reptation of an equivalent primitive chain. From knowledge of the longest relaxation times of the blend components, the stress equation is formulated from which blending laws of viscoelastic properties for the binary blends are derived. To force better agreement between theory and experiment at the pure monodisperse limits of the blends, a crude treatment to include the effect of contour‐length fluctuation in the equivalent‐chain model is also discussed. Theoretical predictions of the zero‐shear viscosity and steady‐state shear compliance are shown to be in good agreement with literature data on undiluted polystyrenes and polybutadienes over a wide range of the blend composition and M2/M1 ratio. The asymptotic of the laws for blends with M2/M1 → 1 and 0 are comparable to those from the relaxation spectrum proposed by others earlier on the basis of the tube model.
Diffusion in concentrated polymer solutions: Encapsulated FENE dumbbell model results
Authors: Brunn P. O. 
Published: April 2003

AbstractStructure‐property relations for the encapsulated FENE dumbbell correlate well with experimental observations for concentrated polymer solutions. Relying on rigorous kinetic theory results, we derive an expression for the polymeric mass flux relative to the mass‐average velocity (diffusive flux). The form of this flux implies non‐Fickian diffusion with its own intrinsic time scale. For steady flow in an infinitely long tube nonuniform concentration profiles are predicted.
Influence of dopant ion and synthesis variables on mechanical properties of polypyrrole films
Authors: Buckley L. J. , Roylance D. K. , Wnek G. E. 
Published: April 2003

AbstractOxidized, conductive poly(pyrrolylium anion) films [poly(pyrrolylium) = PP+ where there exists about one cation per three pyrrole rings] have been prepared electrochemically in an effort to study the effect of counteranion structure and preparation conditions on the composition, order (crystallinity), and mechanical properties of the films. The counteranion principally employed was p‐toluene‐sulfonate (OTs−), although benzenesulfonate (BZs−), p‐ethylbenzene‐sulfonate (EBs−), and p‐dodecylbenzenesulfonate (DBs−) were incorporated in several polypyrrole films. It was found that the amount of OTs− incorporated increased with increasing potential during synthesis, suggesting a parallel increase in the extent of oxidation of the polymer. Mechanical testing of the same films demonstrated that the ultimate tensile strength decreased as the electrode potential and current density during synthesis increased. X‐ray diffraction indicated that the degree of order (reflected by the widths of the diffraction lines), albeit quite small, is dependent upon the anion species and synthesis conditions. Interestingly, samples with the highest degree of order exhibit the highest electrical conductivities.
Interaction via diffusion of polymer crystals in growing spherulites
Authors: Keith H. D. , Padden F. J. 
Published: April 2003

AbstractPrevious calculations of how diffusion ranges should be averaged when polymer molecules of various lengths are segregated at crystal growth fronts have been extended. Crystals of acicular or lamellar habit are addressed directly, necessarily using more approximate methods, and earlier conclusions regarding appropriate averaging are reaffirmed. Results also lead to a better understanding of why crystalline texture in polyethylene spherulites appears to scale with the averaged diffusion range at crystallization temperatures within regime II but not at higher temperatures within regime I.
The thermotropic and lyotropic liquid‐crystalline properties of acetoacetoxypropyl cellulose
Authors: Pawlowski Walter P. , Gilbert Richard D. , Fornes Raymond E. , Purrington Suzanne T. 
Published: April 2003

AbstractAcetoacetoxypropyl cellulose, formed by the acetoacetylation of hydroxypropyl cellulose using a diketene/acetone adduct at elevated temperature, forms both thermotropic and lyotropic liquid‐crystalline phases. DSC and hot‐stage polarized light microscopy confirmed the thermotropic nature of the bulk polymer. Thin layers showed green reflection colors at room temperature. The wavelength λ0of selective reflection was measured spectrophotometrically. The crystalline structure of the polymer was investigated using x‐ray diffraction. A lyotropic mesophase formed in acetic acid at ≥ 40 wt% polymer. The value of λ0for the lyotropic cholesteric mesophase was determined by optical rotatory dispersion (ORD) and circular dichroism (CD) of a thin layer of a wholly anisotropic solution.
Crystallization, thermal behavior, and compatibility in isotactic polystyrene/poly(o‐chlorostyrene‐co‐p‐chlorostyrene) blends
Authors: Silvestre C. , Cimmino S. , Karasz F. E. , MacKnight W. J. 
Published: April 2003

AbstractThe dependence of the kinetics of crystallization and melting behavior in isotactic polystyrene/poly‐o‐chlorostyrene‐co‐p‐chlorostyrene (iPS/Po‐CIS‐co‐p‐CIS) blends on temperature, thermal history, and blend composition has been investigated. The crystallization rate at a given temperature and copolymer composition decreases with increasing copolymer content in the blend when the samples are premelted. These effects can be ascribed to the reduction of mobility of the crystallizable chains due to the presence of the copolymer and to the decrease in the number of heterogenous iPS nuclei as a result of the premelting process. The Avrami exponent values and the analysis of the blend morphology indicate that the growth mechanism of the crystals is strongly influenced by thermal treatment. There is no measurable change in the melting temperature of iPS in the blends, with composition indicating that, on the basis of the Flory‐Huggins approximation of the thermodynamics of polymer mixing, the net interaction parameter at the melting temperature is close to zero. From the comparison of the phase diagram for the isotactic polystyrene‐containing blend with that of the atactic‐containing blend, it can be concluded that in the amorphous state polystyrene with a regular configuration is slightly less compatible with the P(o‐CIS‐co‐p‐CIS) than is polystyrene with random configuration.
Formation of ordered phases of (hydroxypropyl)cellulose in miscible and immiscible isobutyric acid‐water mixtures
Authors: Laivins G. V. , Sixou P. 
Published: April 2003

Abstract(Hydroxypropyl)cellulose (HPC) is known to form birefringent liquid‐crystalline phases at elevated polymer concentrations in either water or isobutyric acid (IBA). The HPC concentration at which the polymeric phase exhibits birefringence decreases as the IBA content in mixed H2O/IBA solvents decreases, even though the concentration ϕic for the formation of an ordered phase of HPC in water is greater than that in IBA. Water is a spectator component and apparently does not participate in the formation of a birefringent phase when IBA is present. A birefringent phase forms once the concentration of HPC in the solution omitting the H2O equals the ϕic of binary HPC/IBA solutions for temperatures from 23 to 95°C. The strong preferential affinity of HPC for IBA is visually evident as an HPC coagulate separates from dilute solution when the solvent mixture contains as little as 5% IBA. The coagulate dissolves to give a monophasic isotropic solution as the IBA content in the solvent is increased. A heterogeneous system in which a clear supernatant fluid covers a pearly white polymeric phase forms when the solvent mixture is immiscible and the HPC content is less than 50%. At high HPC content, the classical appearance associated with concentrated HPC solutions is seen. The optical and rheological properties of the heterogeneous systems are compared with those of homogeneous solutions at several HPC concentrations.
Ion implantation doping and electrical properties of high‐temperature ladder polymers
Authors: Jenekhe Samson A. , Tibbetts Stanley J. 
Published: April 2003

AbstractWe report the first ion implantation doping studies on high‐temperature ladder polymers and show that insulting films of the benzimidazobenzophenanthroline‐type ladder polymer (BBL) can be doped by boron, argon, and krypton implantation to conductivities as high as 224 S/cm at a dose of 4.0 × 1016/cm2 while retaining the excellent mechanical properties of the pristine films. Effects of dose (ions/cm2) and beam current density (microamps/cm2) on electrical conductivity at fixed ion energies are reported. The temperature dependence of the conductivity indicates that the implanted ladder polymer films are semiconductors. Spatially selective implantation, creating regions of conducting lines in an insulating matrix, which suggests microelectronic device applications of the ladder polymers, is demonstrated.
Experimental analysis of the molecular theory of rubber elasticity
Authors: Sanjuan J. , Llorente M. A. 
Published: April 2003

AbstractStress‐strain and birefringence‐strain experiments, on polybutadiene and poly(methyl‐3,3,3, trifluoropropyl siloxane) elastomeric networks of various degrees of crosslinking have been carried out in order to evaluate the recent molecular theory of rubber elasticity of Erman and Flory, which is based on the idea of constraints imposed by entangled network chains on crosslink fluctuations. Previously published results on polyoxypylene and poly(dimethylsiloxane) networks have also been analyzed. In general, the theory describes the elastic behavior of all these systems satisfactorily. Stress‐strain and birefringence data can be interpreted using the same set of parameters. The most important theoretical parameter κ, which is a measure of the severity of constraints, varies with the elastic modulus as predicted by theory. However, the relationship is not a universal one, as was originally suggested.
The effects of solvent type on the concentration dependence of the compression modulus of thermoreversible isotactic polystyrene gels
Authors: McKenna G. B. , Guenet J.‐M. 
Published: April 2003

AbstractSolutions of isotactic polystyrene in either trans‐decalin or 1‐chlorodecane were transformed into gels by quenching from a high temperature (ca. 180°C) to −20°C. The relaxation modulus in compression of these gels was measured over a range of concentrations of from 0.04 g/g to 0.40 g/g. At 22°C, the gels show a double logarithmic stress relaxation rate, m, which is higher than for PVC and gelatin gel systems. 120 s isochronal modulus concentration diagrams exhibit non‐power law behavior, i.e., not only is the general trend such that the double logarithmic slope decreases with increasing concentration, but there are also regions in which abrupt changes in modulus occur over narrow ranges in concentrations. These features in the concentration dependence of the modulus are less pronounced than those found previously1 in isotactic polystyrene/cis‐decalin gels. The behavior is interpreted to be inconsistent with a fringed micelle picture of the gel structure. Preliminary results are reported indicating that polymer fraction and temperature of gel formation can significantly affect the modulus of the gels.
Synthesis and properties of polycyanoethylmethylsiloxane polyurea urethane elastomers: A study of segmental compatibility
Authors: Li C. , Yu X. , Speckhard T. A. , Cooper S. L. 
Published: April 2003

AbstractA series of polyurea urethane block polymers based on either aminopropyl‐terminated polycyanoethylmethylsiloxane (PCEMS) soft segments or soft segment blends of PCEMS and polytetramethylene oxide (PTMO) were synthesized. The hard segments consisted of 4,4′‐methylenediphenylene diisocyanate (MDI) chain‐extended with 1,4‐butanediol. The hard segment content varied from 11 to 36%, whereas the PTMO weight fraction in the soft segment blends varied from 0.1 to 0.9. The cyanoethyl side group concentration was also varied during the synthesis of the PCEMS oligomer. The morphology and properties of these polymers were studied by differential scanning calorimetry, infrared spectroscopy, dynamic mechanical and tensile testing, and small‐angle x‐ray scattering. These materials exhibited microphase separation of the hard and soft segments; however, attaching polar cyanoethyl side groups along the apolar siloxane chains promoted phase mixing in comparison with polydimethylsiloxane‐based polyurethanes. The increased phase mixing is postulated to lead to improved interfacial adhesion and thus can account for the observed improvement in ultimate tensile properties compared with polydimethylsiloxane‐based polyurethanes. Both hard segment content and cyanoethyl concentration are important factors governing the morphological and tensile properties of these polymers.
Morphology of a liquid‐crystalline polyester film
Authors: Bhattacharya S. K. , Misra A. , Stein R. S. 
Published: April 2003

AbstractMorphological studies are reported for a thermotropic liquid crystalline polyester. Small angle light scattering studies were carried out as a function of temperature using Hv and Vv polarization with photographic as well as photometric techniques. No scattering was observed from a thin film cast from a dilute solution of the polymer in a highly volatile solvent. When the film was heated, scattering of light was observed above the glass transition temperature of the polyester. The scattering was found to be azimuthally dependent with Vv intensities being much higher than the corresponding Hv intensities. The size of the morphological features responsible for SALS patterns were calculated and were found not to change significantly with temperature ranging from glass transition temperature to the solid‐nematic transition temperature of the polyester. The WAXS pattern of solution cast polymer was representative of an amorphous structure. Solution cast films heat treated under various conditions (all above the Tg of the polymer) contained crystalline as well as amorphous structures. The maximum apparent crystallinity for annealed samples was of the order of 30%.
Rotating frame proton spin‐lattice relaxation measurements of poly (ethylene oxides)
Authors: Wobst M. 
Published: April 2003

AbstractMeasurements of Tlρ as a function of temperature have been made on two polyethylene oxides (PEO) with molecular masses of 5,000 and 30,000. The T1ρ measurements show biexponential behavior of the relaxation function in the temperature range from 170 K to 350 K. The intensities of the components of the relaxation function are constant over this temperature range in agreement with the crystallinities of the samples. The two relaxation times can be associated with the crystalline and amorphous component; the relaxation time minima describe the α relaxation in the crystalline regions of PEO and the glass transition in amorphous PEO.
Effects of thermal treatment on biaxially oriented poly(ethylene terephthalate). II. The anisotropic glass temperature
Authors: Vallat M.‐F. , Plazek D. J. 
Published: April 2003

AbstractThermal properties of an anisotropic biaxially oriented Poly(ethylene terephthalate) (PET) were determined before and after further deformation of the Mylar film. Film shrinkage in different planar directions was monitored during and following initial heating. After stabilization for three days at 140°C, glass temperatures Tg were determined from the decrease in length of film strips and were found to vary in the different in‐plane directions. An increase in anisotropy brought about by additional deformation in the direction of the greatest orientation enhanced the Tg difference from 8 to 16°C. Tg is highest in the direction of greatest orientation.
Compatibility and mesophase separation in blends of α‐helical polyglutamates
Authors: Sasaki S. , Nagao M. , Gotoh M. , Uematsu I. 
Published: April 2003

AbstractBlends composed of the α‐helical polymers, poly‐L‐glutamates [(NHCαHRC′O)n, R = CH2CH2COO(CH2)m(C6H5] (Lm) and the corresponding D enantiomers (Dm), have been studied by x‐ray diffraction and viscoelastic measurements. Binary blends of L2, D2, L3, and D3 are compatible and form isomorphous mixed crystals at all compositions, whereas other pairs, with the exception of L1/D1, are incompatible. The demixing process is described for a ternary system consisting of L1, D3, and a diluent chloroform at 40°C. The phase diagram comprises four regions, I, IA, A, and AA, with increasing polymer concentration; I: isotropic, A: anisotropic, IA: I–A biphasic, and AA: A–A biphasic. The IA biphasic gap is greater in the ternary system than in the binary ones. The high‐molecular‐weight component (D3) is partitioned into the A phase in the IA region. The AA separation originates from incompatibility of the polymers. The phase behavior is discussed on the basis of the Abe‐Flory theory by incorporating the polymer‐polymer interaction parameter.
Transport of carbon dioxide and methane in glassy aromatic polyesters
Authors: Sheu F. R. , Chern R. T. , Stannett V. T. , Hopfenberg H. B. 
Published: April 2003

AbstractSolubilities and diffusivities of CO2 and CH4 in two aromatic polyesters [Ardel® poly(bisphenol A phthalate) (PAr) and poly(phenolphthalein phthalate) (PPha)] and one polycarbonate [Lexan® (PC)], generated from independent sorption and permeation measurements at 35°C and up to 25 atm, are compared. The permeability ratio for CO2 over CH4, at 20 atm and 35°C, ranges from 24 for PC, to 21 for PAr, and 27 for PPha. However, the permeability of PPha and PAr are 40 and 120% higher, respectively, than that of PC. Less than 21% change in the gas diffusivity was observed; therefore, a major portion of the observed higher permeability of PPha and PAr is attributed to an increase in the gas solubility. These data are interpreted qualitatively in terms of changes in the calculated packing density, chain torsional mobility of the polymer, and gas‐polymer attraction.
Analyzing polymer crazing as quasifracture
Authors: Sun B. N. , Hsiao C. C. 
Published: April 2003

AbstractThis paper deals with a viscoelastic boundary element method for analyzing a polymer quasifracture usually called a craze in polymers. A time‐dependent boundary stiffness is considered on the quasifracture envelope surface. The viscoelastic property of the glassy polymer is represented by a generalized Kelvin model with multiple retardation times. According to the linear viscoelastic correspondence principle, the associated elasticity solution can be solved by applying the general integral boundary element method. Then the viscoelastic solution in the time domain can be obtained by applying a collocation Laplace inversion transformation. Using these methods, the quasifracture problem composed of an isolated craze opening with time‐dependent stiffness traction in a stressed rectangular plate is analyzed. The displacement profile and the stress distribution around the craze envelope surface are computed.
Heat of fusion of poly(4‐methylpentene‐1)
Authors: Charlet Gérard , Delmas Geneviève 
Published: April 2003

AbstractThe heat of fusion of perfectly crystalline poly(4‐methylpentene‐1) (P4MP1), ΔHu, has been determined by two methods. Melting point depressions (A) in concentrated solutions in naphthalene and cyclododecane, and in infinitely dilute solutions in 39 solvents, led to ΔHu = 5.5 ± 0.3 kJ mol−1 (65 ± 4 J g−1). The second method (B) involved new measurements of the crystalline volume Vu,c as a function of temperature, in order to calculate ΔHu from the Clausius‐Clapeyron equation: extrapolation to the melting point gave Vu,c = 109.2 cm3 mol−1 (1.298 cm3 g−1) (I), which is in good agreement with the result of Tanigami et al.1 (II) but appreciably lower than the value reported by Zoller et al.2 (III). Possible reasons for the discrepancy are discussed. The values of ΔHu from methods A and BIII are in excellent agreement, whereas BI and BII give a higher figure. There is at present no reason to prefer one set of values to the other, although the degree of crystallinity estimated from the low ΔHu and the experimental heat of fusion is in the 75–85% range, in excellent agreement with x‐ray diffraction data. Depending on the selected ΔHu, the entropy of fusion is either similar or lower than for other branched polyolefins. The results are discussed in terms of order in the melt, order seemingly relevant to the understanding of the mechanism of formation of the noncrystalline thermoreversible gels of P4MP1.
Infrared reflection‐absorption spectroscopy of polyacrylonitrile on copper and aluminium surfaces
Authors: Wu C. R. , Liedberg B. 
Published: April 2003

AbstractInfrared reflection‐absorption spectroscopy has been used to study the chemical structure of thin films of pyrolyzed polyacrylonitrile (PAN) on copper and aluminium surfaces. The formation of a conjugated CCC backbone occurs at temperatures as low as 200°C for PAN on copper, whereas the same reaction on aluminium requires pyrolysis at 300°C in order to be completed. These temperatures are, respectively, about 200 and 100°C lower than those previously reported for bulk PAN. Pyrolysis of PAN on copper at 200°C also results in diffusion of copper atoms (ions) into the polymer network followed by Cu(I)N°C complexing. Conclusive evidence is obtained for end‐on coordination through nitrogen lone pair orbitals of the CN groups. We propose a chemical structure of PAN on copper that is different to that in the bulk and on aluminium.