bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of morphology on sorption and transport of carbon dioxide in a polyimide from 3,3′,4,4′‐biphenyltetracarboxylic dianhydride and 4,4′‐oxydianiline
Authors: Okamoto Ken‐Ichi , Tanaka Kazuhiro , Kita Hidetoshi , Nakamura Asumaru , Kusuki Yoshihiro
Published: April 2003

Sorption and transport of CO2 have been investigated for polyimide films prepared from 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA) and 4,4′‐oxydianilline (ODA) as well as for a chemically identical commercial polyimide film, Upilex‐R. The BPDA‐ODA polyimide films annealed above the glass transition temperature (270°C) are found to have some degree of ordering owing to molecular aggregation of polymer chains, whereas the films as‐cast are amorphous. The solubility, permeability, and diffusion coefficients decrease significantly with increasing density or increasing average degree of molecular aggregation. The influence of morphology on the parameters in the dual‐mode sorption and transport model has also been investigated. With an increase in density, the Langmuir capacity constant and the diffusion coefficients for Henry's law and Langmuir populations decrease by a larger factor than the Henry's law solubility constant. These results can be tentatively interpreted by assuming either a one‐phase or two‐phase structure for these polyimide films.
Permeation of oxygen dissolved in water through substituted polyacetylene membranes
Authors: Tang Ben‐Zhong , Masuda Toshio , Higashimura Toshinobu
Published: April 2003

The permeation of oxygen dissolved in water through substituted polyacetylene membranes was studied by using an oxygen electrode at 25°C. Many of the membranes (thickness about 200 μm) showed high apparent permeability coefficients P in the range 10−9−10−8 cm3 (STP) cm cm−2s−1 cmHg−1. The resistance r of the boundary layer and the permeability P∞, at infinite membrane thickness were determined from the dependence of P on membrane thickness. The r values of Si‐containing and aliphatic polyacetylenes were usually larger than those of aromatic polyacetylenes. The P∞, values of Si‐containing and aliphatic polyacetylenes agreed closely with the permeability coefficients Pg for gaseous oxygen. In contrast, P∞ values for aromatic polyacetylenes were larger than Pg values.
Direct measurements of the mechanical properties of polymerized and unpolymerized langmuir‐blodgett films
Authors: Halperin K. , Peng J. B. , Sailor M. , Gadwood R. , Ketterson J. B. , Dutta P.
Published: April 2003

Mechanical measurements can be made on Langmuir‐Blodgett (LB) films that have been peeled from their substrates, and are floating on the surface of water, by compressing them between the moving barrier and the Langmuir balance float in a standard monolayer trough. We have used this technique, which utilizes apparatus commonly available where LB films are made, to study multilayers of lead 10,12‐tricosadiynoate (a diacetylene carboxylic acid) that were first polymerized and then peeled from the substrate. For comparison we have performed the same measurements on pieces of mylar, on unpolymerized films, and on films of calcium octadecanoate (a saturated chain fatty acid). We found Young's modulus for films of the saturated chain material, the unpolymerized diynoate, and the polymerized films, to be 6 GPa (900 kpsi), 0.5 GPa, and 6 GPa, respectively.
An iterative procedure based on the donnan equilibrium for calculating the polymer‐subphase volume of alginic acid
Authors: Jang Larry K. , Harpt Nathan , Uyen Ty , Grasmick Daniel , Geesey Gill G.
Published: April 2003

A numerical iterative procedure is presented to predict the polymer‐subphase volume that is formed when anionic polysaccharides such as alginic acid (polyuronic acid from kelp) are suspended in an aqueous solution. (The aqueous region surrounding the polymer chain where a strong electrostatic attractive force for counterions exists is defined as the separate polymer subphase within the colloidal phase enclosed by the polymer coil.) Based on the phase‐partition model of Marinsky et al.5 and Donnan equilibrium theory, this iterative procedure utilizes the base titration data of the acidic polysaccharide at different ionic strengths as well as the osmotic properties of the sodium form of the polysaccharide. No detailed structural information of alginic acid is required. The resulting calculations show that the polymer subphase, which accounts for a small fraction of the total solution volume, should be regarded as the reaction zone for acid dissociation and metal binding reactions. The volume of polymer subphase thus calculated may also serve as an excellent index for the morphology of the polymer molecule at different ionic strengths, degrees of ionization, polymer concentrations, and extent of polymer‐metal binding.
Dielectric relaxation studies of dipolar aromatics in polyethylene. II. Oriented low‐density polyethylene
Authors: Parikh D. , Phillips P. J. , Jang Y. T.
Published: April 2003

Stretched polyethylene has been used for several years by organic spectroscopists as a means of orienting isolated aromatic molecules. Dielectric relaxation studies are reported which consider dipolar aromatic molecules dissolved in stretched polyethylene in order to learn more about the environment of these oriented molecules. The research builds on earlier studies of the dielectric relaxation behavior of dipolar aromatic molecules dissolved in unoriented low density polyethylene. Studies demonstrate that molecules in the amorphous phase are oriented at temperatures below the glass transition, both the β and γ relaxations being orientation dependent. It is shown through studies of oriented rods that large numbers of the orientable molecules are immobilized by the oriented polyethylene and cannot relax. An essential criterion for immobilization to occur is that molecules exhibit geometrical symmetry.
Long periods in slow‐cooled linear and branched polyethylene: Part II
Authors: Rault J. , Robelin‐Souffaché E.
Published: April 2003

It is shown that the long periods L in slow‐cooled polyethylene materials obey the general law L = L0 + αrw, where rw is the weight average dimension of the coil before crystallization, and L0 is a parameter of the order of lc, the crystalline core thickness, which increases as the cooling rate V decreases. α is a parameter independent of M and V but decreasing with the number of long‐chain branches per molecule. The two terms in the above relation are, respectively, the contributions of crystalline and amorphous layers. For cooling rates from 800°C/min to 0.2°C/min, it is shown that the temperature Tc of crystallization is constant; hence the change of morphology (long period, crystalline core thickness, crystallinity) cannot be explained by supercooling. The increase in long period and crystallite thickness in slow‐cooled materials with decreasing cooling rate is interpreted in terms of annealing of the crystallized materials between the crystallization temperature Tc and the secondary transition temperature Tαc. Crystallization proceeds by a two‐step process of solidification and annealing. During the annealing stage, the mobility of the chains in the crystalline phase is due to defects; the kinetics of thickening is then governed by the mobility (or nucleation) of the defects appearing above Tαc. In the proposed model of crystallization, the assumption that the energy of activation is proportional to Tαc explains the observed laws L ≡ lc ≡ log ta, where the annealing time ta is equal to (Tc − Tαc)/V. The model applies also to polymers crystallized from the melt and subsequently annealed.
A study of the mechanical anisotropy in shear of high‐draw, low‐draw, and voided poly(vinylidene fluoride)
Authors: Lewis E. L. V. , Ward I. M.
Published: April 2003

The mechanical anisotropy in shear of oriented from I poly(vinylidene fluoride) sheet has been studied, completing the measurement of all nine independent compliances for this material. The morphology is parallel‐crystallite; however, the crystalline regions are not lamellar in shape, but take the form of blocks with a bricklike shape oriented along the draw direction. The results have been analyzed in terms of a three‐dimensional generalization of the Takayanagi model. First, modelling of the three principal extensional compliances based on previous measurements indicates that the gaps between the crystalline units are smaller in the transverse directions than in the draw direction. A voided sample shows a marked increase in the transverse compliances of the amorphous regions and considerable anisotropy owing to the voids. Secondly, a novel development of the Takayanagi model has been made to analyze the shear behavior. This has enabled the calculation of the shear compliances of the amorphous regions and indicates that the larger magnitude of the shear compliance in the plane normal to the draw direction is due to the large magnitude of the corresponding amorphous shear compliance, and that this is not affected by increased draw ratio or by the voids.
Solid‐state carbon‐13 NMR Studies of vulcanized elastomers. V. Observation of new structures in sulfur‐vulcanized natural rubber
Authors: Andreis Mladen , Liu Juwhan , Koenig Jack L.
Published: April 2003

The complementary application of the NMR inversion recovery measurements and the computer fitting of the overlapping spectral region is found to be a useful method for structural analysis of vulcanized natural rubber in the solid state. Since the linewidths in 13C‐NMR spectra of solids are relatively broad compared with the differences between chemical shifts, some weak signals are completely obscured in the resulting spectra. If the resonances have sufficiently different relaxation times, such as methyl and methylene carbons, it is possible to detect neighboring heavily overlapped signals by using the inversion recovery delay τ value at which the interfering strong resonance has null intensity. The 20 resonances observed in the spectra of crosslinked rubbers are tentatively assigned to the structural units formed during the vulcanization process. It is found that vulcanizates containing smaller amounts of sulfur (1 and 3%) show insignificant changes in the NMR spectra for curing times of 30 and 90 min. Structural modifications in rubbers cured with 10% sulfur continuously increase with the increasing curing time up to 120 min, indicating a significant loss in double bonds in the later stages of the reaction.
Correlation of glass transition temperature and molecular weight: A model based on the principle of corresponding states
Authors: Dibenedetto A. T. , Dilandro L.
Published: April 2003

The molecular weight dependence of the glass transition temperatures of polystyrene, polyα‐methyl styrene, polyisopropylα‐methyl styrene, polymethylmethacrylate, polyvinylchloride, poly‐isobutylene, polyisoprene, and poly‐N‐octadecylmaleimide is described by an equation developed from the Principle of Corresponding States. A statistical analysis is used to test the adequacy of the equation, and it is shown that from a statistical point of view the three molecular parameters, Se/Sm, ε/ε, and Ce/Cm, characterizing, respectively, the ratios of contact area, lattice energy, and segmental mobility of end groups relative to repeating segments along the chain, will adequately describe the data. It is also shown that in one limit the equation reduces to the well‐known Ueberreiter‐Kanig result, which for most cases is a good first approximation to the data. The molecular weight‐TG data were used to estimate the depression of the glass transition temperature of polystyrene and polymethylmethacrylate by a series of plasticizers. It was concluded that in the absence of important changes in the molecular structure within a homologous series of polymers, the Principle of Corresponding States can be employed to describe the molecular weight dependence of glass transition temperature over the entire range of available data.
Epitaxial growth of long‐chain molecules on potassium hydrogen phthalate and potassium chloride substrates from the vapor phase
Authors: Zhang W. P. , Dorset D. L.
Published: April 2003

Pentacontane, hexacontane, 15‐ketohentriacontane (palmitone), and solid solutions of the two n‐paraffins were deposited from the vapor phase onto surfaces of potassium hydrogen phthalate (PHP) crystals and cleavage faces of potassium chloride (KCl) crystals in vacuo. Epitaxial growth, with molecular chains parallel to the substrates, occurs within a temperature range (e.g., 25–50°C for palmitone), and the epitaxial relationship between molecules and substrates was broken at higher temperatures. The electron diffraction patterns, similar to that of polyethylene, were obtained from all samples prepared at room temperature. The [100] or [130] directions of palmitone crystals are parallel to the substrate surface of PHP, and the [110] direction is parallel to that of KCl; the crystals in both cases are the orthorhombic form with lattice parameters a = 7.56 Å, b = 4.93 Å, c = 82.8 Å and a space group of Pna21. The (100) planes of n‐paraffin crystals are parallel to the surface of PHP, and the crystals are again orthorhombic. Also, solid solutions of n‐paraffins can be formed from the vapor phase, with the nucleation process on the two substrates being the same as for pure paraffins.
A dynamical study of the melting behavior of polypivalolactone single crystals by the X‐ray diffraction method
Authors: Kawaguchi Akiyoshi , Murakami Shozo , Kajiwara Kanji , Katayama Ken‐ichi , Nerger Dittmar
Published: April 2003

Wide‐angle and small‐angle X‐ray diffraction patterns of polypivalolactone single crystals were recorded as a function of temperature while heating at a constant rate. Long periods were found to increase abruptly at a certain temperature, while the degree of crystallinity decreased up to that temperature and then recovered on further heating, to an extent depending on the rate of heating. Multiple endotherms were observed in DSC measurements. The temperature at which the first endotherm peak was observed corresponded exactly to the temperature of the long period jump mentioned above. From these data, it is concluded that the original lamellar crystals melt at each peak temperature in the DSC thermogram and new lamellae are produced by subsequent crystallization. Multiple endotherms in the DSC thermogram are thus considered to represent repeated melt‐recrystallization processes.
Fiber formation from liquid‐crystalline precursors. II. Cellulose in N,N‐dimethylacetamide‐lithium chloride
Authors: Bianchi E. , Ciferri A. , Conio G. , Tealdi A.
Published: April 2003

Fibers were spun from isotropic and biphasic solutions of regenerated cellulose (DP = 290) in N, N‐dimethylacetamide +7.8% LiCl using water as a coagulant. There is an increase in mechanical properties through the isotropic → anisotropic transition with moduli reaching 22 GPa. The problem with this system is that crystallization encroaches on the biphasic region, and a pure mesophase is never observed. However, owing to the slow nucleation rate of the crystals, a biphasic solution is stable for a long time and can be spun to yield high modulus and orientation. The best approach is to use small flow gradients (extrusion rate and pick‐up ratio) and to allow long times for homogenization and nucleation of the mesophase.
Transport studies with model membrane
Authors: Siddiqi Fasih A. , Alvi Naved Iqbal
Published: April 2003

The most recent theory for salt concentration dependence of biionic potential, developed by Ikeda and his colleagues on the basis of thermodynamics of irreversible processes, has been compared with that of Nozaki et al. to get a relationship for the calculation of theoretical values of biionic potential. The latter are in good agreement with the experimental data gathered for the parchment‐supported manganese ferricyanide membrane in contact with various alkali chloride solutions.

The conclusion of selectivity sequence of group Ia cations, reached on the basis of measurements of biionic potentials, is consistent not only with the findings of thermodynamic effective fixed charge density, evaluated by utilizing membrane potential equations provided by nonequilibrium thermodynamics, but also with the data on activation parameters calculated by making use of the theory of absolute reaction rates.

The values of impedance Z, membrane resistance Rm, and membrane capacitance Cm have also been evaluated on the basis of a simple equivalent circuit model. Impedance values follow the theoretical predictions at high frequencies, but at lower frequencies there is a marked deviation from the ideal behavior probably due to roughness and nonhomogeneity of the membrane used in this investigation.
Plastic yielding of partially crystalline polymers
Authors: Gent A. N. , Madan S.
Published: April 2003

Measurements are described of characteristic stress‐strain properties in tension for several representative partially crystalline polymers prepared by cooling from the melt. Striking differences were found in the natural draw ratio, ranging from 2x to 11x. They are interpreted in terms of a simple molecular model of the yielding process in which polymer chains, folded to different degrees in the crystallites, are pulled taut. Values of yield and draw stress were found to be of the same order as the free energy Um of melting, suggesting that yielding and drawing take place by stress‐induced disruption of crystallites, analogous to melting. The mechanical work of drawing was similar to, but generally larger than, that required for melting, ranging from Um to about 4Um. The difference is attributed to strain energy of drawn material and possible recrystallization during drawing.
A procedure for predicting sorption equilibrium in ternary polymer systems from Flory–Huggins binary interaction parameters and the inversion point of preferential solvation
Authors: Campos Augustín , Gavara Rafael , Tejero Roberto , Gómez Clara , Celda Bernardo
Published: April 2003

A procedure has been developed, based on the Flory–Huggins theory as generalized by Pouchlý, which permits the calculation of preferential (λ) and total (Y) sorption coefficients from previous information on the binary interaction parameters, χ, χ, and g12(ϕ10) and on the mixture composition at which the sign of λ inverts. The expressions obtained were applied to 10 cosolvent polymer systems for which experimental values of λ and Y are known. Practically in all the studied systems, the theoretical predictions are in fair accordance with the experimental data.
Polymerization of diethynyldiphenylmethane: DSC, FTIR, NMR, and dielectric characterization
Authors: Nguyen H. X. , Ishida H. , Hurwitz F. I. , Gorecki J. P. , D'Amore L. , Hyatt L. H.
Published: April 2003

4,4′‐Diethynyldiphenylmethane thermally polymerizes by a free radical mechanism to a highly crosslinked structure of interest as a high temperature composite matrix resin. The polymerization reaction was characterized by differential scanning calorimetry, Fourier‐transform infrared (FTIR) spectroscopy, 1H and 13C nuclear magnetic resonance (NMR) spectroscopy, and microdi‐electrometry. The predominant reaction mechanism appears to be linear polymerization through the acetylene end groups, which follows first‐order kinetics. However, during the early stages of reaction a second, more rapid polymerization mechanism is evident; it is postulated that this is the formation of a cyclic trimer, which is kinetically favored but sterically prohibited as the crosslinked network grows. Formation of a liquid crystalline trimer is hyppthesized; such intermediate formation is supported by intensity increases in the aromatic region of the NMR spectra, by FTIR difference spectroscopy comparisons with model compounds, and by enhancement of conductivity as observed by microdielectrometry.
Solvent‐induced embrittlement in a crystallizable polyarylate
Authors: Berger Larry L.
Published: April 2003

The effects of solvent‐induced crystallization on the micromechanical properties of thin films of polyarylate (PAr) were studied. Under uniaxial extension amorphous polyarylate was observed to deform exclusively by shear deformation with no evidence of crazing. Upon exposure to methylethyl ketone, vapor, or liquid, PAr crystallizes and is subsequently embrittled. Our transmission electron microscopy results clearly show that this embrittlement results from a transition in plastic deformation mechanism from shear yielding to crazing. A detailed examination of the samples revealed that the crazes formed preferentially within the noncrystalline regions and that the craze tips followed a complex trajectory around the crystallites. In some cases the craze tip advance deviated by as much as ±30 from a direction normal to the tensile axis. Because crazes are inherently more susceptible to forming cracks than shear deformation zones, crystallization reduces the fracture toughness of the polymer. This type of embrittlement, via a transition in plastic deformation mechanism, is believed to be a general behavior for solvent‐crystallizable thermoplastics.
Development of supermolecular structure in polystyrene latexes
Authors: Yang Se‐in , Klein A. , Sperling L. H.
Published: April 2003

The development of supermolecular structure in polystyrene latex particles was investigated by small‐angle neutron scattering (SANS). Seed latexes of deuterated polystyrene were swollen with an equal mole‐% of protonated styrene monomer, equilibrated, and polymerized to complete conversion. The scattering patterns reflect the extent of supermolecular structure development inside the particle. The data were analyzed by separating the Debye single‐chain and spherical scattering form factors. The extent of segregation was found to depend on the relative size of the chains compared with that of the particle, going through a maximum at the ratio Mw/D of about 0.1, where Dw represents the weight‐average diameter of the latex particle. When the chain dimensions are relatively very small, uniform molecular mixing is obtained. The best model for the segregated system is a graduated core‐shell supermolecular structure.
On the Pace–Datyner theory of diffusion of small molecules through polymers
Authors: Kloczkowski A. , Mark J. E.
Published: April 2003

The Pace–Datyner theory for diffusion of penetrant molecules in polymers has been analyzed. It has been found that the correct solution of the problem they pose is possible only at 0 K, since then the separation of two chains at x = ∞ is equal to the minimum of the DiBenedetto potential for their interaction. Otherwise the energy of symmetrical separation is infinite. By using the linearization method to solve the differential equation, Pace and Datyner neglected the problem of unnatural boundary conditions at x = ∞ for temperatures above 0 K. The exact numerical solutions of differential equations at temperature 0 K were therefore compared with the results of the Pace–Datyner linear approximation. For temperatures different from 0 K the solution of the problem is possible only when the proper cutoff is imposed. The analytical expression for the coeffients in the DiBenedetto potential has been found, and the potential can be written as
Growth and decay of concentration fluctuations in polymer–polymer mixtures
Authors: Ohnaga Takashi , Inoue Takashi
Published: April 2003

A computer simulation based on the Cahn–Hilliard nonlinear diffusion equation, developed in the field of metallurgy, is applied to the demixing behavior of a polymer–polymer mixture. The simulation is a one‐dimensional version. Spatially periodic concentration fluctuations appear at a very early stage and evolve with the wave number almost constant. Later some waves are absorbed into neighboring ones, resulting in a decrease in the average wave number of the concentration fluctuation. Thus, characteristic phenomena in the demixing are successfully described by the computer simulation. Furthermore, the simulated time variation of wave number agrees with experimental results in the literature. The analysis is extended to two‐step quenching: after a homogeneous mixture undergoes the first temperature‐jump from the single‐phase region to the two‐phase region of the phase diagram, the system is allowed to demix isothermally for a time, and then the demixed system undergoes the second jump to deeper or shallower quench. When the quench depth of the second jump (ΔT2) is smaller than half the first depth (ΔT1), the concentration fluctuation as developed under ΔT1 decays with time after the second jump. When ΔT2 is between ΔT1 and (ΔT1/2), the fluctuation decays slightly after the second jump and then increases. When the second jump is to a deeper quench (ΔT2 > ΔT1), a new fluctuation of short wavelength is superimposed on the previously developed one.
Sharp fronts due to diffusion and stress at the glass transition in polymers
Authors: Cohen Donald S. , White Andrew B.
Published: April 2003

We derive and analyze a model for sharp fronts in glassy polymers. We take the major effect of a diffusing penetrant on the polymer entanglement network to be the inducement of a differential viscoelastic stress. This couples diffusive and mechanical processes through a viscoelastic response where the strain depends upon the amount of penetrant present. Analytically, the major effect is to produce explicit delay terms, via a relaxation parameter, to account for the fundamental difference between a polymer in its rubbery state and the polymer in its glassy state, namely the finite relaxation time in the glassy state owing to slow response to changing conditions. We produce concentration profiles in good agreement with observations on sharp front formation. In addition the model can account for the phenomenon of sorption overshoot.
Transitions and morphology of a thermotropic liquid‐crystalline polyester with a flexible spacer
Authors: Hu Shiru , Xu Mao , Li Jianchang , Qian Baogong , Tao Kung , Lenz Robert W.
Published: April 2003

The mesomorphic transitions, crystallization from the mesophase, and the influence of the specimen preparation method on the solid‐state structure of an aromatic polyester containing a triad aromatic ester mesogenic group and a decamethylene flexible spacer in the main chain were studied by DSC, SALS, WAXS, polarizing microscopy, torsional braid analysis, and depolarizing transmittance techniques. The specimens obtained from solution were semicrystalline and exhibited nematic mesophase formation above the melting point Tm, whereas the melt‐cast specimens were mesomorphic as cast. A transition from the nematic phase to another mesophase, designated Mx, is proposed to occur below Tm, so this transition is monotropic. It appears that the transition to the Mx mesophase occurs before, and may even be a prerequisite for, crystallization of the melt‐cast specimens. The thermal expansion coefficient of the anisotropic melt is close to that of the isotropic melt, and the Tg of the supercooled solid mesophase is close to that of the amorphous phase.
Poly(ethylene oxide)/poly(ethyl methacrylate) blends: Crystallization, melting behavior, and miscibility
Authors: Cimmino Sossio , Martuscelli Ezio , Silvestre Clara , Canetti Maurizio , De Lalla Claudia , Seves Alberto
Published: April 2003

Results of an investigation of isothermal crystallization and thermal behavior of poly(ethylene oxide)/poly(ethyl methacrylate) (PEO/PEMA) blends are reported. The blend composition and the crystallization temperature strongly influence the crystallization process from the melt and the melting temperature of PEO. The addition of PEMA to PEO causes a depression in the spherulite growth rate, in the overall kinetic crystallization constant, and in the melting temperature. Experimental data on the radial growth rate G and overall kinetic rate constant Kn are analyzed by means of the latest kinetic theory. From this analysis it emerges that the crystallization of pure PEO and PEO in the blend conforms to the regime I process of surface secondary nucleation. The depression of the melting temperature cannot be explained only in terms of a diluent effect due to the compatibility of the two components in the melt. Annealing and morphological effects, dependent on composition and time, must also be taken into account.
A nonequilibrium thermodynamic description of dilute polymer solutions
Authors: Pérez‐García C. , Casas‐Vázquez J. , Lebon G.
Published: April 2003

The purpose of this paper is to justify the well‐known relaxation spectra observed in dilute polymer solutions from extended irreversible thermodynamics. This is performed by elevating the viscous stress tensor to the status of independent variable, in addition to the usual variables, like temperature and mass density. In particular, it is shown that our thermodynamic description encompasses the Rouse and Zimm models. Memory functions for the longitudinal and transverse correlation functions are derived and analyzed within the frame work of molecular hydrodynamics.
Investigations of comblike polysiloxanes. I. The influence of spacer length on dielectric relaxation studies of aligned samples
Authors: Simon R. , Coles H. J.
Published: April 2003

Dielectric relaxation studies on aligned liquid‐crystalline comblike polysiloxanes are presented. The polymers differ only in the length of the flexible spacer separating the mesogenic side groups from the polysiloxane backbone. The characteristic features of the observed relaxation process as a function of frequency and temperature, in both the liquid‐crystalline and isotropic phases, are described, and the effect of the spacer length is discussed. Within the liquid‐crystalline phase a narrow single loss process is observed, due to the relaxation of the mesogenic side groups around the polymer backbone, whereas in the isotropic phase a much broader loss curve is seen. The transition from an aligned polymer mesophase to the randomly aligned isotropic phase is also studied in detial, and comparison with earlier work on comblike polyacrylate and methacrylate liquid crystals is presented.
Fiber spinning from the nematic melt. VI. Flow instabilities in the 30:70 copolyester of hydroxybenzoic acid and 2‐hydroxy‐6‐naphthoic acid
Authors: Yang D.‐K. , Krigbaum W. R.
Published: April 2003

The rheological behavior and fiber spinning are investigated for the Celanese liquid crystal copolyester 30 mol% p‐hydroxybenzoic acid and 70 mol% 2‐hydroxy‐6‐naphthoic acid (designated as 30HBA/70HNA) with inherent viscosity 7.8 dL/g. Shear thinning viscosity, and yield stress are observed at low shear stress, which probably results from the existence of crystallites in the melt.

The crystal‐nematic melting point of the copolymer, as measured by differential scanning calorimetry, is around 309°C. Extrudates are collected at four different temperatures ranging from 315 to 345°C. Melt fracture and die swell are observed above 335°C at low shear stress. A wide‐angle x‐ray diffraction (WAXS) study of an annealed sample indicates that the abnormal phenomenon may be due to crystallites arising from blocky units of HNA. Fiber spinning is performed at high shear rate at 325 and 335°C. Flow is stable under these conditions. The spin draw ratio is the ratio of take‐up velocity to the velocity of extrudate existing from the capillary. The initial modulus reaches a maximum at a fairly low spin draw ratio. Instron and wide‐angle x‐ray (WAXS) studies show that the mechanical properties and orientation are poor for the fiber spun near the crystal‐nematic melting point. Also, thermal history is found to affect the rheological behavior. Heat treatment offibers, particularly those which are well oriented, brings an improvement of mechanical properties.
Texture development in polyethylene. I. Uniaxial extension and uniaxial compression
Authors: Krause Stephen J. , Hosford W. F.
Published: April 2003

Texture development of high‐density polyethylene has been studied by x‐ray diffraction at various strains for uniaxial extension, as achieved by uniaxial tension and extrusion, and for uniaxial compression. Pole distributions were measured for the (100), (200), (020), and (011) reflections. Textures were described by ideal single‐crystal orientations with inverse pole figures. In uniaxial extension, samples were deformed up to true strains of 1.83 (reductions of up to 84%). After a strain of 0.55, the c axis oriented at 35° from the extension axis and with increasing strain approached the extension axis. This was attributed to initial (110) or (310) twinning in combination with (100) slip, followed subsequently by [001] slip. In compression, samples were deformed up to true strains of 1.83 (reductions up to 84%). The texture consisted of strong components of the compression axis near (100) and weaker components near (110). At higher strains the intensity of the near‐(100) components decreased, whereas the near‐(110) components became more intense. The near‐(100) components are explained by slip on (100) planes. The growth of the near‐(110) components at the expense of the near‐(100) components can be explained by relaxation twinning of the near‐(100) components.
Texture development in polyethylene II. Unidirectional rolling
Authors: Krause Stephen J. , Hosford W. F.
Published: April 2003

The effect of degree of strain on texture development in high‐density polyethylene has been studied by pole figure analysis for unidirectional rolling. The crystallite orientation distribution in rolling textures has been quantified with an efficient technique which fits three‐parameter, two‐dimensional Gaussian‐type distributions to pole figure intensity data around ideal single crystal orientations. During flat rolling of polyethylene a texture consisting of a strong (100) [001] component and a weak (110) [001] component develops continuously from the lowest true strain of 0.24 (21% reduction) up to the highest true strain of 1.36 (74% reduction). The peak intensity of the Gaussian distributions of both (100) [001] and (110) [001] components increase continuously to the highest strain. The maximum angular breadth of both component distributions, which are roughly perpendicular to the strain direction, remains constant with increasing strain. The minimum angular breadth of both component distributions, which are roughly parallel to the strain direction, decreases continuously owing to gradual alignment of the covalently bonded chain backbone parallel to the strain direction. The development of the (100) [001] component is explained by slip on (100) planes while the weak (110) [001] component is explained by slip on (110) planes. Although the latter component was previously attributed to (110) or (310) relaxation twinning, this seems unlikely because of the lateral constraint during plane strain deformation conditions used in this study.
Comparison of three models for permeation of CO2/CH4 mixtures in poly(phenylene oxide)
Authors: Story Brooks J. , Koros W. J.
Published: April 2003

Two models for the permeability of pure gases have been extended to include binary gas mixtures. The first is an extension of a pure gas permeability model, proposed by Petropoulos, which is based on gradients of chemical potential. This model predicts the permeability of components in a gas mixture solely on the basis of competition for sorption sites within the polymer matrix. The second mixed gas model follows an earlier analysis by Barrer for pure gases which includes the effects of saturation of Langmuir sites on the diffusion as well as the sorption processes responsible for permeation. This generalized “competitive sorption/diffusion” model includes the effect of each gas component on the sorption and diffusion of the other component in the mixture. The flux equations from these two models have been solved numerically to predict the permeability of gas mixtures on the basis of pure gas sorption and transport parameters. Both the mixed gas Petropoulos and competitive sorption/diffusion model predictions are compared with predictions from the earlier simple competitive sorption model based on gradients of concentration. An analysis of all three models is presented for the case of CO2/CH4 permeability in poly(phenylene oxide) (PPO). As expected, the competitive sorption/diffusion model predicts lower permeability than either of the models which consider only competitive sorption effects. The permeability depression of both CO2 and CH4 predicted by the competitive sorption/diffusion model is roughly twice that predicted by the competitive sorption model, whereas the mixed gas Petropoulos model predictions for both gases lie between the other two model predictions. For the PPO/CO2/CH4 system, the methane permeability data lie above the predictions of all three models, whereas CO2 data lie below the predictions of all models. Consequently, the competitive sorption/diffusion model gives the most accurate prediction for CO2, while the simple competitive sorption model is best for methane. The effects of mixed gas sorption, fugacity, and CO2‐induced dilation were considered and do not explain the inaccuracies of any of the models. The relatively small errors in mixed gas permeability predictions using either of the three models are likely to be related to “transport plasticization” of PPO owing to high levels of CO2 sorption and its effect on polymer segmental motions and gas diffusivity.
Treatment of asymmetric SANS data
Authors: Hammouda Boualem
Published: April 2003

Small‐angle neutron scattering (SANS) is a useful technique for investigating the anisotropy of density fluctuations when these have single orientation direction. The commonly used method for treating asymmetric SANS data is to analyze sectors of data parallel and perpendicular to the orientation axis. Other methods based on the use of all the available two‐dimensional (2D) data are discussed. These consist in least‐squares fitting of the 2D data to models that include nonuniform deformations of the sample. An inverse 2D Fourier transform of the raw data has also been used to obtain an asymmetric pair correlation function. A hot stretched partially deuterated homopolymer and a stretched microphase segregated rubbery random copolymer system are used as examples of anisotropic scatterers.
X‐ray diffraction by thermotropic main‐chain polymers with side groups. II. semiflexible polyesters
Authors: Chin Hui H. , Azároff Leonid V. , Saini Agya R. , Lenz Robert W.
Published: April 2003

Semiflexible thermotropic aromatic polyesters with lateral groups were aligned magnetically and mechanically in monodomains after separation into high‐molecular‐weight (polymer) and low‐molecular‐weight (oligomer) fractions. Based on the x‐ray intensity distributions recorded for a series of seven different substituents in the arylsulfonyl substituted group, a novel smectic structure was determined for H, F, Cl, OCH3, and CH3 in the para position while a normal nematic alignment prevailed when it contained Br or NO2.
A Study of the dielectric properties of the polymer electrolyte PEO‐LiClO4 over a composition range using time domain spectroscopy
Authors: Gray F. M. , Vincent C. A. , Kent M.
Published: April 2003

High frequency dielectric measurements in the range 10 MHz to 10 GHz have been performed on poly(ethylene oxide) (PEO) and its complexes with lithium perchlorate using time domain spectroscopy. Measurements were made over a wide polymer‐to‐salt composition range and in the temperature range 50–75°C. All samples were amorphous. A relaxation was observed for PEO and its complexes with LiClO4 in the GHz region and is attributed to the β (αa) relaxation arising from long‐range segmental motion of the polymer or the ion‐polymer complex. Good agreement was found between conductivity values determined by TDS and those quoted in the literature An increase in salt concentration in the polymer increases the distribution of relaxation times which may be explained in terms of increased intermolecular and intramolecular transient crosslinks. The dispersion amplitude (ε−ε) has a maximum value between an O/Li ratio of 20:1 and 12:1 and shows a similar dependence on salt concentration as the conductivity.
XPS studies of charge transfer interactions in some polyphenylacetylene‐electron acceptor systems
Authors: Kang E. T. , Neoh K. G. , Tan K. L. , Tan B. T. G.
Published: April 2003

X‐ray photoelectron spectroscopy (XPS) studies have been performed on charge transfer complexes of trans‐polyphenylacetylene (PPA). The acceptors used included halogens, such as I2 and Br2, and organic electron acceptors, such as 2,3‐dichloro‐5,6‐dicyano‐p‐benzoquinone (DDQ), chloranil, fluoranil, and 7,7,8,8‐tetracyano‐p‐quinodimethane (TCNQ). Incomplete and relatively weak charge transfer interactions were observed in most of the complexes. These help to account for the relatively low conductivity levels observed in most of the PPA complexes when compared with the corresponding complexes of other conjugated polymers. PPA has also been found to interact with molecular oxygen to some extent in solution. In complexes involving O2, Br2, and fluoranil, XPS data suggest that the charge transfer interaction may have proceeded further than the pure formation of molecular charge transfer complexes.
The time of flight static secondary negative ion mass spectra of poly(methylmethacrylate), poly(ethylmethacrylate), and poly(methylmethacrylate‐co‐ethylmethacrylate). Ion structures and quantification
Authors: Lub J. , van Vroonhoven F. C. B. M. , van Leyen D. , Benninghoven A.
Published: April 2003

Negative secondary ion mass spectra of poly(methylmethacrylate) (PMMA), poly(ethyl‐methacrylate) (PEMA), and two copolymers of methylmethacrylate (MMA) and ethylmethacrylate (EMA) are presented. The spectra were obtained with a time of flight‐static secondary ion mass spectrometer without charge compensation. The structures of typical ions in the mass range 20–220 amu are given, and the intensities of these ions were used to obtain some quantitative information about the ion formation processes. It is shown that quantification of a simple two‐component system like the copolymers mentioned above is rather straightforward.
The effect of electrolyte‐controlled growth morphology on the charge transport properties of poly(3‐methylthiophene)
Authors: Reynolds John R. , Hsu Shing‐guang , Arnott Howard J.
Published: April 2003

Poly(3‐methylthiophene) films were potentiostatically and galvanostatically synthesized on platinum electrodes in acetonitrile using lithium perchlorate, lithium tetrafluoroborate, tetra‐n‐butylammonium perchlorate, and tetra‐n‐butylammonium tetrafluoroborate as supporting electrolytes. Cyclic voltammetric analyses of the polymer films indicate the synthesis is polymerization process dependent. Constant potential syntheses, which resulted in a higher current density and were carried out at higher potentials, yielded polymer films with a higher charge capacity. Chronocoulometric results show that the charge transport rates of the films were electrolyte dependent and that tetra‐n‐butylammonium tetrafluoroborate yielded poly(3‐methyl‐thiophene) with the highest charge transport rate. The charge transport rate was found to be electric field dependent for all cases, suggesting that the films resemble a porous electrode. Scanning electron microscope analyses of the films, prepared under various conditions, indicate that the synthesis method used, and the nature of the electrolyte, strongly influence morphology and charge transport.
Thermodynamics of the glass transition
Authors: Astarita Gianni , Paulaitis M. E. , Wissinger R. G.
Published: April 2003

A thermodynamic analysis of the glass transition in polymers is presented, which predicts, with a minimum of assumptions, three of the four inequalities which have consistently been observed experimentally: i.e., that specific heat and isothermal compressibility of the glass are lower than those of the rubber, and that the Prigogine‐Defay ratio is larger than unity. The analysis cannot predict the fact that the thermal expansion coefficient of the glass is also lower than that of the rubber, and indeed the converse situation is not a thermodynamic impossibility.
Comparative study of the phase behavior of liquid‐crystalline components in closely related blends and copolyesters
Authors: Lenz Robert W. , Rao A. Kameswara , Reddy C. Rami , Bafna Sudhir , Bhattacharya Subrata
Published: April 2003

Phase behavior of blends of a liquid‐crystalline (LC) polymer with a non‐LC polymer and of a series of copolymers containing mesogenic and nonmesogenic units was studied by thermal, optical, and dynamic mechanical methods. The polymers composing the blends and the copolymers had the same constituent monomers. The blends exhibited phase separation over the whole range of compositions studied as observed by DSC and dynamic mechanical analysis. Two glass transition temperatures (Tg) corresponding to the two components and independence of melting (Tm) and isotropization temperatures (Ti) to changes in composition were observed for the blends. The copolymers did not show phase separation over most of the composition range studied. Only one Tg corresponding to that of the major component could be detected for the copolymers, and the Tg was found to increase with an increase in the amount of nonmesogenic monomer in the copolymers. The difference in phase behavior was explained on the basis of the chemical environment of the constituent units in the blends and in copolymers. Phase inversion in the blends was observed by microscopy when the blends contained 60 mol% or more of the non‐LC polymer.
A light‐scattering study of phase separation kinetics in polystyrene/poly(2‐chlorostyrene) blends
Authors: Takahashi Masato , Kinoshita Satoshi , Nose Takuhei
Published: April 2003

The angular dependence of the intensity of scattered light from polystyrene/poly(2‐chlorostyrene) blends was measured as a function of time in early and late stages of phase separation. The results were discussed in terms of Cahn's theory and scaling law for the late stage. Some distinctive behaviors which had not been found in other polymer blends were observed: the intensity of low‐angle scattering increased significantly during phase separation, possibly because of inhomogeneities in density. In the power laws km α tϕ and Im α tθ for the time (t) evolution of the peak position km and peak heigh Im of the structure function in the late stage; the value of ϕ was around −1, almost independent of composition and temperature; the ratio |θ/ϕ| was less than the theoretical value 3. Possible explanations for these behaviors are discussed in relation to the glass transition.
Investigations of a series of PPDI‐based polyurethane block copolymers. I. General morphology
Authors: Kazmierczak M. E. , Fornes R. E. , Buchanan D. R. , Gilbert R. D.
Published: April 2003

The morphology of a series of segmented polyurethane block copolymers is characterized by x‐ray scattering, differential scanning calorimetry (DSC), density measurements, and tensile studies. The materials contain hard segments formed from paraphenylene diisocyanate (PPDI) and flexible segments formed from poly(oxytetramethylene) (POTM) ranging in molecular weight from 650 to 2000. Four different molecular weight compositions were investigated, with the weight fraction of the hard segment (wh) ranging from 0.14 to 0.33. The microphase structure has been examined using small‐angle x‐ray scattering, and the microphase transition zone thickness is estimated to be on the order of 1 nm. Oriented samples have been characterized with wide‐angle x‐ray scattering, and the flexible segment is shown to undergo stress‐induced crystallization. DSC thermograms show flexible segment melting in the compositions containing the highest two molecular weights of the flexible segments. The hard segment thermal transitions were complex with a broad melting peak that varied with weight fraction and with a high temperature transition attributed to regions with hard segment lengths longer than the bulk of the hard segment component. There is an increase in tensile strength and initial modulus and decrease in elongation with increasing wh. Density data suggest the existence of a multiphase system.