bluuebunny/crossref_metadata_2025 huggingface dataset:
A dielectric study of chain motions in poly(vinyl methyl ether)
Authors: Pathmanathan K. , Johari G. P.
Published: April 2003

The dielectric permittivity and loss of poly(vinyl methyl ether) (mol. wt. 30,000) have been measured from 12 Hz to 100 kHz at temperatures from 77 K to 320 K. Two relaxation processes, γ and β, are observed at T < Tg (245 K), and one above Tg. The Arrhenius plots of the γ and β processes have activation energies of 20 and 41 kJ mole−1 respectively. The relaxation rate of the α process is described by the Vogel‐Fulcher‐Tamman equation or the William‐Landel‐Ferry equation. The relaxation rates of γ and β processes evaluated from the isochrones differ from those evaluated from the isothermal spectrum. The features of chain motions observed are similar to those in other polymer and rigid molecular glasses.
Properties of iodine complexes of monosubstituted polyacetylenes
Authors: Petit Michel A. , Soum Alain H. , Leclerc Mario , Prud'Homme Robert E.
Published: April 2003

Iodine complexes of six monosubstituted polyacetylenes with methyl, ethyl, propyl, pentyl, t‐butyl, and phenyl substituents have been characterized by electronic spectroscopy. UV spectra allow the determination of the nature and the amount of active species, and photoelectronic spectra confirm the nature of these species. These measurements indicate the presence of iodine in the I and I2 forms. The concentration of I is low (0.12–4.0 mol%), and it depends on the nature of the substitutent, but this amount does not decrease when the films are left under vacuum. On the other hand, the adsorption of ε high concentration of iodine is possible; this adsorption is governed by a diffusion mechanism and is reversible. Iodine doping leads to a cis‐to‐trans isomerization of the polymers, except for poly(3‐3‐dimethyl‐1‐butyne), which can be isomerized to the cis or to the trans form, depending on the solvent employed. Electrical properties of polymer I complexes are also reported. Conductivities of about 10−4 Ω−1 cm−1 are obtained for all polymers in the presence of an excess of iodine.
Influence of structural and morphological factors on the mechanical properties of the polyethylenes
Authors: Popli Rakesh , Mandelkern Leo
Published: April 2003

Force‐length relations at ambient temperature have been determined for a set of polyethylenes which represent a wide range in molecular weight and molecular constitution. Taking advantage of previous work from this laboratory, samples have been prepared in such a manner that the important independent structural variables can be identified and isolated and their influence on the different aspects of the deformation process assessed. Partial melting‐recrystallization processes appear to play an important role. For the linear polymers there is a direct influence of molecular weight. The influence of molecular weight manifests itself in the structure of the interlamellar zone which has a major influence on the initial modulus as well as the ultimate properties. Copolymers and branched copolymers display quite different behavior. The most striking difference is the invariance of the ultimate properties with molecular weight, branching, and level of crystallinity. From the set of experimental results that are presented the molecular factors involved in the deformation process can be sorted out. It becomes quite evident that all of the basic structural regions, characteristic of semicrystalline polymers, contribute to the observations. Focus solely on the changes in the crystallite, in analogy to the deformation of small‐molecule crystalline systems, is inadequate in the case of crystalline polymers.
Large edge‐excitation red shift for a merocyanine dye in poly(vinyl alcohol) polymer matrix
Authors: Al‐Hassan Khader A. , El‐Bayoumi M. Ashraf
Published: April 2003

The observed large edge‐excitation red shift of the fluorescence of a merocyanine dye in a polyvinyl alcohol polymer matrix is explained in terms of a matrix that is rigid enough at room temperature to prevent complete equilibration between different solvation sites.
Thermal properties of thermotropic polyesters with rigid chains
Authors: Kyotani Mutsumasa , Yoshida Katsumi , Ogawara Kaoru , Kanetsuna Hisaaki
Published: April 2003

The relationship between chemical structure and thermal properties of three polyesters composed of rigid backbone units,
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and
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here X = Br (A), Y = Cl (B), and Y = Methyl (C), was studied by differential scanning calorimetry, x‐ray diffraction, and polarized‐light microscopy. The effect of annealing on the polyesters was also investigated. Polymer A forms an anisotropic melt phase at temperatures above 280°C, but decomposes at temperatures in the range of the anisotropic melt phase. The thermal properties of polymer B are very similar to those of polymer C. Anisotropic‐isotropic melt transitions were observed at temperatures below 400°C in both heating and cooling runs for polymers B and C. These two polymers do not decompose thermally up to 400°C. A polymer with chlorine as a substituent on the hydroquinone ring in the main chain shows a wider range of temperatures at which the anisotropic melt phase exists. Quenched films of the polymers are very poorly crystalline or almost amorphous. Textures observed in anisotropic melt phases are largely preserved in the quenched films. The temperatures of the crystal‐anisotropic melt and anisotropic‐isotropic melt phase transitions become higher with annealing.
Entanglement between dissimilar chains in compatible polymer blends: poly(methyl methacrylate) and poly(vinylidene fluoride)
Authors: Wu Souheng
Published: April 2003

The plateau modulus and zero‐shear melt viscosity of binary compatible blends of poly(methyl methacrylate) and poly(vinylidene fluoride) were measured by dynamic oscillation and shear creep, and used to analyze the entanglement between dissimilar chains and its effect on melt viscosity. It is found that dissimilar chains are less likely to entangle with each other than similar chains, resulting in a large reduction of zero‐shear melt viscosity in this system.
Determination of the crystalline and noncrystalline molecular orientation in oriented polypropylene by infrared spectroscopy
Authors: Mirabella Francis M.
Published: April 2003

The application of orientation to enhance the properties of a wide range of macromolecular materials has stimulated an interest in the characterization of the effects of such orientation processes. In semicrystalline polymers, this requires the characterization of the orientation in both the crystalline and noncrystalline phases. An infrared dichroism method was developed to simultaneously measure the orientation in the crystalline and noncrystalline phases of polypropylene. The method was applied to a series of melt‐crystallized and gel‐crystallized polypropylene specimens drawn up to a maximum of about 50 ×. The Hermans orientation functions of each phase were determined. The crystalline orientation was found to increase rapidly and approach perfect orientation at relatively low draw ratio (i.e., > 10 × ). However, the noncrystalline orientation was found to increase much more slowly up to about 50 × draw ratio. The Youngs modulus was found to increase nearly linearly up to about 50 × and to correlate with the increase in the noncrystalline‐orientation function and not with the crystalline‐orientation function.
A visualization study of polyethylene terephthalate flow using a pseudohyperbolic die geometry
Authors: Ihm Dae Woo , Cuculo John. A.
Published: April 2003

Flow visualization studies were made during extrusion by using a hyperbolic die, streak photography, and flow birefringence techniques. Velocity was found to be a linear function of position along the die axis. This is equivalent to a constant elongational strain rate. Considering that the hyperbolic die maintains the stretching rate achieved in the upstream over an extended time period, this profile seems to be the optimum die design for maximum chain‐ordering potential. A unique analysis of the birefringence and velocity distribution data allowed determination of characteristic relaxation time for the PET melt of 5.5 × 10−3 at 285°C.
Ionomeric blends. V. FTIR studies of ionic interactions in polyurethane‐styrene blends
Authors: Tannenbaum Rina , Rutkowska Maria , Eisenberg Adi
Published: April 2003

FTIR spectra of blends of lightly sulfonated polystyrene (PS‐SSA) with polyurethanes (PU) containing a tertiary nitrogen in the chain extender were recorded. These blends exhibit a two‐phase behavior, but the individual components are not phase separated. Earlier dynamic mechanical studies suggested the occurrence of proton transfer from the sulfonic acid to the tertiary nitrogen, which enhanced the miscibility via ionic interactions and resulted in the formation of a miscible blend between the PS‐SSA and the hard segment of the PU, the soft segment being excluded. FTIR studies of these blends now confirm the proton transfer mechanism. A new absorption band at 3428 cm−1 corresponds to a stretching vibration of an N+−H bond. The 1012 cm−1 band of the SO3H group, which strongly depends on the degree of protonation, shifts to lower frequency. The symmetric stretching vibration of the SO group, which occurred at 1043 cm−1, shifts to lower frequency as well, suggesting a lower polarization of the SO dipole due to the removal of H+.
Polystyrene in cyclopentane: Dilute solution properties from the upper critical to the lower critical solution temperature
Authors: Berry Guy C. , Casassa Edward F. , Liu Pi‐Yao
Published: April 2003

Dilute solutions of polystyrene in cyclopentane are studied with four narrow‐distribution polymer fractions ranging in molecular weight from 1.6 × 105 to 1.8 × 106. Light scattering (total intensity) and viscosity measurements cover a temperature range spanning both “theta” temperatures: the limiting upper critical solution temperature (19.6°C) and the limiting lower critical temperature (154.5°C). Within experimental uncertainty, chain dimensions are the same at the two theta temperatures. Correlations among second virial coefficients, mean‐square molecular radii of gyration, and intrinsic viscosities, are analyzed. Temperature and molecular‐weight dependences are correlated satisfactorily in terms of the excluded‐volume parameter z that is central to the “two‐parameter” theories of dilute solution behavior. The data can also be correlated in the framework of the newer renormalization theories.
Laser light scattering study of polyacrylamide gels
Authors: Sellen D. B.
Published: April 2003

Laser light scattering experiments with polyacrylamide gels containing diffusing bovine plasma albumin are described. Complete heterodyne beating has not been assumed, and an account is given of a novel method for finding the degree of spectral broadening by scanning angles of scatter while measuring the temporal autocorrelation function. Results obtained by this method for polyacrylamide gels and un‐cross‐linked solutions in the absence of diffusing protein, are compared with those of other authors. In the presence of the protein there is a complex interaction between the diffusion coefficient of the protein and the coefficient associated with the diffusing fluctuations in segment density of polyacrylamide. The diffusing protein dominates at low gel concentrations, and the gel density fluctuations dominates at high gel concentrations. It is proposed that the protein preferentially occupies the less dense regions of the gel, so that at low gel concentrations, where it diffuses faster than the gel fluctuations, it tends to cancel them out, whereas at high gel concentrations where the protein is highly impeded by the gel structure, it tends to be carried along by the gel density fluctuations.
Increase in crystallinity in poly(vinylidene fluoride) by electron beam radiation
Authors: Pae K. D. , Bhateja S. K. , Gilbert J. R.
Published: April 2003

We examine the influence of high‐energy radiation and subsequent aging and orientation on the degree of crystallinity of poly(vinylidene fluoride) (PVDF) films. In particular, PVDF films were exposed to electron beam radiation (doses up to 50 Mrad) and aged at room temperature for varying lengths of time followed by uniaxial orientation. The degree of crystallinity of these films was found to increase significantly with increasing radiation dose. In addition, a further substantial increase in the degree of crystallinity was observed upon subsequent aging of irradiated films at room temperature. Upon orientation, in addition to a further rise in the degree of crystallinity, the crystallites were observed to undergo the α form → β form transformation, the latter phase being the polar phase effective for piezo‐electric/pyroelectric activity.
Configurational effects on polystyrene rejection from microporous membranes
Authors: Adamski Robert P. , Anderson John L.
Published: April 2003

Dilute solutions of polystyrene in chloroform were filtered through track‐etched mica membranes. The pores of each membrane were smaller than the mean unperturbed dimension of the polymer molecules. Three configurations of polystyrene were used: linear, comb‐branched, and star‐branched. The data for the linear polystyrenes show that the reflection coefficient σ decreases with solvent flow rate per pore q in a manner independent of molecular weight. At low flow rates the rejection is quantitatively described by 1 − σ ∼ q1.69. Comparisons among the three configurations show that as the extent of branching increases, σ increases at given solvent flow rate. It is concluded that filtration studies with well‐defined porous membranes can provide a relative measure of deformability among various configurations of polymeric species.
High‐energy ion implantation of polymers: Poly(ethylene terephthalate)
Authors: Balik C. M. , Said M. A. , Carlson J. D.
Published: April 2003

The effect of high‐energy ion implantation of oxygen into a thin film of poly(ethylene terephthalate) (PET) was studied by Fourier transform infrared spectroscopy and differential scanning calorimetry (DSC). Mylar samples 13 μm thick were implanted with 6‐MeV oxygen ions at fluences ranging from 5 × 1012 to 2 × 1014 ions/cm2. The DSC data showed a substantial loss of crystallinity, even at the lowest fluence, which extended deeper into the polymer film than the predicted range for oxygen deceleration in PET. Solubility measurements indicated the presence of cross‐linking, especially at the highest fluence, but bands due to cross‐linking could not be detected in the infrared. The trans/gauche ratio for the glycol group conformation was measured by a pair of conformationally sensitive infrared bands. Surprisingly, the conformation of the glycol segments did not change appreciably with increasing fluence, although crystallinity decreased and degree of cross‐linking increased. The implications these results have on possible mechanisms of chemical and physical alterations of the polymer structure by ion implantation are discussed.
Solution properties of ultrahigh molecular weight polymers. VII. Conformational characteristics of poly(butyl methacrylate)
Authors: Simionescu Bogdan C. , Ioan Silvia , Simionescu Cristofor I.
Published: April 2003

The paper is concerned with light scattering studies on solutions of ultrahigh molecular weight poly(butyl methacrylate). The dependence of the radius of gyration and of the second virial coefficient on the weight‐average molecular weight of the polymers was established in methyl ethyl ketone, dimethylformamide, and CCl4. Short‐range and long‐range interactions were discussed in terms of the steric factor σ, of the interaction parameter B, and of the interpenetration function ψ(z).
Dynamic mechanical properties of homogeneous copolymers of ethylene and 1‐alkenes
Authors: Clas S.‐D. , McFaddin D. C. , Russell K. E.
Published: April 2003

The dynamic mechanical properties of homogeneous copolymers of ethylene with 1‐butene, 1‐octene, and 1‐octadecene prepared by means of a vanadium‐based catalyst system have been determined. The 1‐butene copolymers show α′ and α transitions in the 20–60°C temperature range, whereas the 1‐octene and 1‐octadecene copolymers show single α transitions. The intensity of the β transition increases with comonomer content in 1‐butene and 1‐octene copolymers and also with the amount of interfacial material present. In ethylene‐1‐octadecene copolymers, this intensity is comparatively low, even though there is about 20% interfacial material present. The implications of these results with regard to the nature of interfacial material are discussed.
Polymerization beyond the gel point. I. The molecular weight of sol as a function of the extent of reaction
Authors: Argyropoulos Dimitris S. , Berry Richard M. , Bolker Henry I.
Published: April 2003

Theoretical expressions for describing the weight‐average molecular weights of the soluble fractions from polymerizations obtained beyond the gel point were tested experimentally. The theory of branching processes and a recursive approach essentially based on the method of Macosko and Miller were found to be virtually equivalent. The soluble fractions produced from the stoichiometric polymerization of 1,3,5‐benzenetriacetic acid (BTA) with decamethylene glycol (DMG) gave molecular weights and distributions in excellent qualitative agreement with the theory. The results are interpreted in terms of intramolecular cyclization, diffusion, and the presence of microgel particles.
Effect of molecular weight distribution and structure of LDPE on its deformation behavior in a high‐temperature region
Authors: Enikolopian N. S. , Akopian E. L. , Styrikovitch N. M. , Ketchekian A. S. , Nikolskii V. C.
Published: April 2003

The effect of molecular weight distribution (MWD) (the low‐molecular weight “tail” in particular) on the deformation behavior of low‐density polyethylene (LDPE) during uniaxial stretching was studied over the temperature range from 293 K to the melting point. Four types of film samples were used: untreated polyethylene (PE), the same PE subjected either to solvent extraction or to thermal degradation, and PE with extracted fractions replaced by a low‐molecular weight paraffin analog. Graphs of elongation at break εb versus temperature always exhibited a minimum that occurred in the neighborhood of 370 K. The shape of the curve, the amount that εb decreases with increasing temperature, as well as the absolute values of εb strongly depend on the type of sample. The εb for a degraded PE is markedly lower than that for an untreated one. On the other hand, the extraction of low‐molecular weight fractions leads to a higher εb, especially in the premelting region. The low‐molecular weight “tail” has a different effect from that of added paraffin. This appears to be due to the plasticizing effect of the latter. The effect of temperature is much more pronounced on the work of deformation (Ad) than on εb. The results obtained were interpreted on the assumption that structural (phase) inhomogeneity of LDPE is the key factor determining the deformation behavior of polymer over the studied temperature range.
Structure‐permeability relationships in silicone polymers
Authors: Stern S. A. , Shah V. M. , Hardy B. J.
Published: April 2003

Permeability coefficients P for He, O2, N2, CO2 CH4, C2H4, C2H6, and C3H8 in 12 different silicone polymer membranes were determined at 35.0°C and pressures up to 9 atm. Values of P for CO2, CH4, and C3H8 were also determined at 10.0 and 55.0°C. In addition, mean diffusion coefficients D and solubility coefficients S were obtained for CO2, CH4, and C3H8 in 6 silicone polymers at 10.0, 35.0, and 55.0°C. Substitution of increasingly bulkier functional groups in the side and backbone chains of silicone polymers results in a significant decrease in P for a given penetrant gas. This is due mainly to a decrease in D, whereas S decreases to a much lesser extent. Backbone substitutions appear to have a somewhat lesser effect in depressing P than equivalent side‐chain substitutions. The selectivity of a silicone membrane for a gas A relative to a gas B, i.e., the permeability ratio P(A)/P(B), may increase or decrease as a result of such substitutions, but only if the substituted groups are sufficiently bulky. The selectivity of the more highly permeable silicone membranes is controlled by the ratio S(A)/S(B), whereas the selectivity of the less permeable membranes depends on both the ratios D(A)/D(B) and S(A)/S(B). The permeability as well as the selectivity of one silicone membrane toward CO2 were significantly enhanced by the substitution of a fluorine‐containing side group that increased the solubility of CO2 in that polymer.
Structural changes in poly(L‐alanine) induced by heat treatment
Authors: Tsukada Masuhiro , Nagura Masanobu , Ishikawa Hiroshi
Published: April 2003

Structural changes in poly(L‐alanine)(PLA), a model compound related to tussah silk fibroin, induced by heat treatment have been studied by differential thermal analysis, x‐ray diffraction, and infrared spectroscopy. PLA heated below 300°C shows x‐ray patterns very similar to those of the α‐helix crystalline phase, in addition to the diffraction patterns due to the β structure. Samples heated at 368°C exhibit predominantly the diffraction patterns due to the β crystalline phase. From infrared spectra, PLA samples heated below 280°C are found to be composed of all three molecular conformations: β sheet, random coil, and α helix. The intensity of the infrared absorption at 650 cm−1 (amide V) assigned to the random coil conformation is decreased by heat treatment above 325°C. The content of the β‐sheet structure remains almost constant when the specimen is heated below 325°C, and increases abruptly on heating to around 335°C, while the random coil content is decreased abruptly by heat treatment above 335°C. The α‐helix content does not change, regardless of heat treatment. It is suggested therefore that the random coil conformation of PLA transforms directly into the β sheet on heat treatment above 335°C.
The effect of electron irradiation on the structure and mechanical properties of highly drawn polyethylene fibers
Authors: Klein P. G. , Woods D. W. , Ward I. M.
Published: April 2003

Two very different high‐modulus polyethylene fiber samples, a low molecular weight melt‐spun and drawn fiber, and a high molecular weight gel‐spun and drawn fiber, have been subjected to electron beam irradiation to various doses in vacuum and in the presence of acetylene. The gel content after irradiation in acetylene was found to be much greater than for an equivalent dose in vacuum. The gel content–dose relationship could not be described by either Charlesby–Pinner analysis or the Inokuti equation. This is attributed to the polydispersity and the complications introduced by the unique morphologies of highly drawn fibers. Following previous studies, the tensile creep behavior was interpreted in terms of a model comprising two thermally activated processes in parallel, a low stress process relating to the amorphous network, and a high stress process relating to the continuous crystal fraction. Analysis of the creep behavior of the melt‐spun, low molecular weight fiber irradiated in vacuum revealed crosslinking in the amorphous regions and chain scission in the crystal. Chain scission was found to be much reduced when irradiating in acetylene, for which a mechanism has been proposed. The creep rates and activation volumes of the high molecular weight, gel‐spun fiber were found to be significantly lower, probably due to the unique morphology. In this case the dominant effect of irradiation on the mechanical properties can be attributed to chain scission rather than crosslinking.
Heat capacity measurements in carboxylic polyelectrolyte solutions
Authors: Yamashita F. , Kwak Jan C. T.
Published: April 2003

Apparent molal heat capacities as a function of the degree of neutralization have been determined for dilute aqueous solutions of poly(acrylic acid) (PAA), poly(methacrylic acid) (PMA), copoly(maleic acid‐ethylene) (MAEt), and copoly(maleic acid‐styrene) (MASt) using direct flow microcalorimetry. Apparent molal volumes were measured as well. Both molal heat capacity and molal volume decrease with increasing ionization of the polymer. The effect of the hydrophobic interactions of the methyl group or phenyl group was obtained from the difference in the molal quantities of PMA and PAA, or MASt and MAEt. No evidence of hydrophobic effects, as determined from the heat capacity, was found for the conformational transition of PMA, but the hydration of the phenyl groups in MASt was found to be changed significantly at a degree of neutralization of 0.4.
A comparison of spin relaxation and local motion between symmetrically and asymmetrically ring‐substituted bisphenol units in dissolved polycarbonates
Authors: Ratto J. A. , Inglefield Paul T. , Rutowski R. A. , Li K.‐L. , Jones Alan Anthony , Roy Ajoy K.
Published: April 2003

Carbon‐13 and proton spin‐lattice relaxation times were measured at two field strengths on solutions 10% by weight of two polycarbonates in C2D2Cl4 from −20 to +120°C. The first polycarbonate is an asymmetrically substituted form with one chlorine on one of the two phenylene aromatic rings of the bisphenol unit, whereas the second polycarbonate is symmetrically substituted with two chlorines on each of the two rings. The nuclear spin relaxation data are interpreted in terms of several local motions likely in these polymers. Segmental motion was described by the Hall–Helfand correlation function. Segmental motion in the monosubstituted polycarbonate is somewhat slower than in unsubstituted polycarbonate, whereas segmental motion in the tetrasubstituted polycarbonate is considerably slower. Phenylene ring rotation is observed in unsubstituted polycarbonate and in the monosubstituted polycarbonate above 40°C. Below 40°C in the monosubstituted species, and at all temperatures in the tetrasubstituted species, ring rotation is replaced by ring libration as the predominant motion contributing to spin lattice relaxation. In addition, the rotational motion of the two types of rings in the asymmetric monosubstituted form are very similar although not identical. The substituted ring is slightly less mobile than the rings of unsubstituted polycarbonate. This indicates a strong coupling of ring motion, although the coupling leads to less than synchronous motion. Methyl group rotation is present in both polymers and is little affected by the various structural modifications.
Solute–solvent interactions of oligo(m‐benzamide)s in N,N‐dimethylacetamide
Authors: Kojima Takakazu , Hamada Masahiko , Miyahara Masa‐Aki , Hosaka Yoshinobu
Published: April 2003

Studies on solute–solvent interactions of oligo(m‐benzamide)s in N,N‐dimethylacetamide (DMA) have been carried out. The enthalpies of solution have been measured for oligo(m‐benzamide)s and oligo(m‐phenylene)s in DMA and benzene. Contributions of enthalpies of cavitation and dispersion interaction to the enthalpy of transfer from benzene to DMA, ΔHtr (Ben → DMA), have been examined for oligo(m‐phenylene)s. A considerable contribution of excess enthalpy, ΔHE (Ben → DMA), to ΔHtr (Ben → DMA) has been found, which increases with the number of benzene rings of the solute. By assuming that ΔHE (Ben → DMA) of diphenyl (DP) is equal to that of benzanilide (BA) in DMA, the amide hydrogen bond enthalpy of BA in DMA, ΔH estimated by “the pure base method” corrected for the enthalpies of cavitation and dispersion interaction. The ΔH value has been given by the following expression including the unknown solubility parameter of BA, δBA:

The evaluation of δBA has resulted in the conclusion that −ΔH is smaller than 10.9 kJ mol−1. Moreover, ΔHtr (TMU → DMA) for oligo(m‐benzamide)s has been examined. It has been shown that the amide hydrogen bonding ability of DMA is lower than that of TMU. The linearity of the plot of ΔHtr (TMU → DMA) against the number of amide bonds in the molecule has been explained by the increase in hydrogen bond enthalpies with the number of amide bonds in the molecule.
Crystallization of bisphenol a polycarbonate induced by supercritical carbon dioxide
Authors: Beckman Eric , Porter Roger S.
Published: April 2003

Supercritical carbon dioxide readily induces crystallization in bisphenol A polycarbonate. Crystallization begins within one h of exposure to the CO2 at temperatures and pressures as low as 75°C and 100 atm. The degree of crystallinity increases sharply as the CO2 pressure is raised from 100 to 300 atm but levels off thereafter. This behavior is likely due to a minimum in the Tg of the polycarbonate/CO2 mixture owing to the opposite effects of the pressure on the Tg of the polymer and on the equilibrium weight fraction of CO2 absorbed. Percent crystallinities of over 20%, comparable to that achieved using acetone or other organic liquids, have been obtained after 2 h exposure to supercritical CO2. Since polycarbonate degasses quickly and quantitatively at ambient temperature and pressure, the high Tg of bisphenol A polycarbonate can be regained in the crystallized material without further vacuum treatment.
Random homogeneous sodium sulfonate polysulfone ionomers: Preparation, characterization, and blend studies
Authors: O'Gara John F. , Williams David J. , Macknight William J. , Karasz Frank E.
Published: April 2003

The sodium salts of randomly sulfonated polysulfone (Na‐SPSF), derived from 1,1′‐sulfonylbis‐[4‐chlorobenzene] with 4,4′‐(1‐methylethylidene)‐bis‐[phenol], were prepared over the composition range of 3–30 mol% sodium sulfonate, using improved procedures in which the sulfonating complex was introduced into an intensely agitated polymer solution. In contrast to earlier work, Tg was found to increase nonlinearly with sodium sulfonate content. A SAXS study provided no evidence of ionic clustering in these polymers. Binary blends of Na‐SPSFs differing only in composition were prepared by casting films from solution, and their phase behavior was studied by dynamic mechanical analysis after annealing at 250°C. It was found that the blends were miscible up to a composition difference of about 9–10 mol% sodium sulfonate. Using this fact it was possible to calculate a value for χABn of 200–250, where χAB represents the segmental interaction parameter between unmodified and modified repeat units, and n is the degree of polymerization. Uncertainty in the degree of ionic association places a degree of uncertainty on the effective value of n and therefore on χAB. The product, however, is independent of any assumptions regarding molecular associations.
Effect of doping on thermoluminescence in polymers. II. Polycarbonate doped with triphenyl methane and xanthene dyes
Authors: Vanderschueren J. , Linkens A. , Niezette J.
Published: April 2003

The thermoluminescence (TL) of polycarbonate doped with triphenyl methane and xanthene dyes was measured following irradiation with ultraviolet light at 77 K and the effect exercised by systematically varying excitation wavelength, irradiation dose, and dopant concentration were investigated. The TL glow curves are characterized by two distinct peaks that can be attributed to genuine emissions of the dopant‐polymer systems and involve continuous distributions of apparent activation energies as determined by partial heating techniques. The low‐temperature peak extends over the temperature interval corresponding approximately to the complex β relaxation of the polymeric units (short‐range chain motions), but no obvious correlation between the two phenomena can be evidenced because the TL peak is never structured and the values and type of evolution of apparent activation energies as a function of temperature are clearly different from those observed for the β relaxation. In this temperature range the TL properties are consistent with an ionization of the dye followed by a recombination process involving electron tunneling from trap to luminescence center rather than thermal excitation. The second TL peak appears in a unusually high temperature region (> 250 K) where no intrinsic relaxation of the polymeric matrix is known to occur. This is not to say that the chain motions cannot contribute to some extent to the detrapping processes. Generally speaking, however, the TL results show that interpreting glow curves only in terms of relaxation processes should be done with great caution and that in certain cases an observed emission must be considered as specific to the dopant‐polymer system rather than to the polymer itself.
Thermal expansion of irradiated polytetrafluoroethylene
Authors: Subrahmanyam H. N. , Subramanyam S. V.
Published: April 2003

The thermal expansion coefficient of gamma‐irradiated Polytetrafluoroethylene (PTFE) has been measured in the temperature range 80–340 K by using a three‐terminal capacitance technique. The samples are irradiated in air at room temperature with gamma rays from a Co60 source at a dose rate of 0.26 Mrad/h. The change in crystallinity is measured by an x‐ray technique. The expansion coefficient is found to increase with radiation dose below 140 K owing to the predominant effect of degradation. Above 140 K, the expansion coefficient is found to decrease with radiation dose because of the enhanced crystallinity. The temperatures of the two first‐order phase transitions are also found to shift to lower temperatures owing to degradation of PTFE.
Styrene‐terminated polysulfone reactive oligomers: Cure and properties
Authors: Garcia Dana
Published: April 2003

Oligomers end‐capped by groups capable of thermally induced polymerization have found wide applications in advanced structural composites and adhesives. The styrene‐terminated polysulfone reactive oligomers described in this paper represent an example of such thermosetting systems. The advantage of these compounds, over high molecular weight polysulfone resin, lies in their easier processing and improved solvent resistance. This paper addresses the properties of the neat oligomer as a function of initial molecular weight and those of the resulting cured resin as well as a complete characterization of the curing reaction. Furthermore, a comparison will be made between these oligomers and the better known acetylene‐terminated sulfone oligomers.
Calorimetric study of blends of poly(butylene terephthalate) and a liquid crystalline polyester
Authors: Paci Massimo , Barone Corrado , Magagnini Pier Luigi
Published: April 2003

The thermal properties of solution‐prepared blends of poly(butylene terephthalate) (PBT) and liquid crystalline poly(biphenyl‐4,4′‐ylene sebacate) (PB8) have been studied by differential scanning calorimetry (DSC). The smectic‐to‐isotropic (s → i) transition of the mesomorphic component is observed at temperatures slightly increasing with the PB8 content, in the 270–280°C range; on cooling, the mesophase formation (i → s transition) takes place at temperatures that decrease markedly with decreasing PB8 content. The temperatures of the crystal‐to‐smectic and smectic‐to‐crystal transitions of PB8 are almost invariant with blend composition. The melting and crystallization temperatures of the PBT phase decrease on increasing the content of the liquid crystalline component.

These results, together with those of isothermal calorimetry of both the crystallization of the PBT component and the mesophase formation of the PB8 component of the blends, indicate that the two polymers are not immiscible in the isotropic state. In this latter state, however, the two polyesters undergo transesterification, which can be followed through changes in the DSC scans. The effect of the thermal history on the properties of the blends has been studied with particular attention. Both the dynamic and the isothermal calorimetric measurements provide evidence of an increase of the degree of crystallinity of PBT on addition of the liquid crystalline component up to about 35–50% by weight.
Morphological partitioning of chain ends and methyl branches in melt‐crystallized polyethylene by 13C‐NMR
Authors: Pérez E. , Vanderhart D. L.
Published: April 2003

The partitioning of methyl and vinyl ends between the crystalline and noncrystalline regions of polyethylene has been investigated using 13C‐NMR in the solid state. The polyethylene samples, which were crystallized from the melt, varied in molecular weight, polydispersity, crystallization rate, and comonomer content. For the limited set of samples considered, the ratio of crystal to overall end concentration is independent of those variables. This ratio takes the values of 0.75 and 0.60 for the methyl and vinyl ends, respectively. When the crystalline fraction of these samples is taken into account, 50–75% of the total saturated ends and 42–63% of the total vinyls reside in the crystal. For an ethylene/propylene copolymer, 21–27% of the methyl branches were determined to be in the crystal. This level of incorporation puts methyl branches in a position intermediate between chain ends and ethyl branches.
Mechanical and dielectric relaxations of epoxide resins containing the spiro‐ring structure. II. Effect of the introduction of methoxy branches on low‐temperature relaxations of epoxide resins
Authors: Ochi Mitsukazu , Yoshizumi Makoto , Shimbo Masaki
Published: April 2003

Mechanisms for low‐temperature relaxations of three spiro‐ring‐type epoxide resin systems with and without methoxy branches were investigated by comparison with those of a bisphenol A‐type resin system. In the spiro‐ring‐type epoxide resin systems, two well‐defined relaxation peaks, denoted as the β and β′ relaxations, and a shoulder peak were observed at about −70, +60, and 0°C, respectively. The magnitude of the β relaxation was decreased by the introduction of methoxy branches on the phenylene group. This phenomenon could be interpreted as a result of the formation of hydrogen bonds between the hydroxy‐ether group and methoxy branch. Moreover, it was concluded that the β′ relaxation and the shoulder peak are due to the motion of the p‐phenylene group adjacent to the spiro‐ring and of the hydroxy‐ether group blocked by the hydrogen bond, respectively.
WAXS studies on block copolymers of ethylene and propylene
Authors: Mo Zhishen , Wang Lixiao , Zhang Hongfang , Han Ping , Huang Baotong
Published: April 2003

Wide‐angle X‐ray scattering from presumed block copolymers of polypropylene (PP) and ethylene‐propylene copolymer (EPR), i.e., PP‐EPR and PP‐EPR‐PP, synthesized by sequential polymerization with δ‐TiCl3Et2AlCl, was examined and compared with WAXS of mechanical blends and chain‐transfer mixtures of PP and EPR with comparable compositions. The peak at 2θ = 20° for both the copolymers and the mixtures was attributed to the γ modification of PP in EPR. A strong variation in the ratio of diffraction intensities I040/I110 of PP in block copolymers and mixtures was explained in terms of crystallite growth in different directions. Analysis of the patterns and calculation of crystallinity, crystallite size, and lattice parameters led to the conclusion that block structure existed in the prepared copolymers.
Dynamics of a single copolymer chain
Authors: Benmouna M. , Duval M. , Borsali R.
Published: April 2003

The dynamics of a single copolymer chain in a solution containing identical chains is studied. The intermediate scattering function is calculated, and two different modes are identified and analyzed as a function of wave vector q. The first mode is characteristic of the copolymer system and leads to a peculiar constant relaxation frequency as q goes to zero. The second mode represents the diffusion of the chain in the solution.
Kinetics of mesophase formation and crystallization in poly(diethylsiloxane)
Authors: Papkov V. S. , Svistunov V. S. , Godovsky Yu. K. , Zhdanov A. A.
Published: April 2003

Optical and calorimetric studies of the kinetics of mesophase formation and crystallization in poly(diethylsiloxane) have been conducted. The mesomorphic phase is found to grow from the isotropic melt in the form of lamellar domains about 2 μm thick in the temperature range 293–307 K. According to birefringence data, macromolecules in the mesomorphic lamellae are perpendicular to the end faces. The kinetics of mesophase formation obey the Avrami equation with the morphological parameter n close to 2 (it is equal to 1.75 ± 0.05), which corresponds to the two‐dimensional growth of the mesomorphic phase from athermal nuclei. The limiting conversion of the isotropic melt was shown to be temperature‐dependent. This is likely to be connected with a change in the number of nuclei with temperature. The crystallization of polymer from the mesomorphic state occurs with retention of the optical texture of the sample. The process proceeds not as a sporadic crystallization of individual mesomorphic lamellae but as a growth of the nucleated crystalline regions via a consecutive incorporation of adjacent crystallizing lamellae.
Surface‐enhanced raman scattering from poly(4‐vinyl pyridine)
Authors: Roth P. G. , Boerio F. J.
Published: April 2003

Surface‐enhanced Raman scattering (SERS) has been observed for poly(4‐vinyl pyridine) absorbed onto silver island films. Bands near 1219 and 1613 cm−1, which are weak in normal Raman spectra of PVP, are strong in SERS spectra, and the band near 1020 cm−1, which is the strongest band in the normal spectra, is relatively weak in SERS. The strongest bands in the SERS spectra all belong to the same symmetry species as αZZ, implying that the pyridine moieties are adsorbed through the nitrogen atoms with a vertical conformation. The ring breathing mode of the pyridine rings is observed near 1020 cm−1, a frequency characteristic of pyridinium ions or coordinated pyridine, providing further evidence for adsorption through the nitrogen atoms. Silver catalyzed photooxidation, which can lead to the appearance of artifacts in SERS spectra, particularly of polymers, can be reduced by overcoating SERS samples with thin films of polymers such as poly(methyl methacrylate) that have low Raman scattering cross sections.
Prediction of the glass transition temperature of polymers: A model based on the principle of corresponding states
Authors: DiBenedetto A. T.
Published: April 2003

The application of corresponding state principles to describe the properties of polymers is implicit in many of the fundamental studies of polymeric behavior. The seminal works of Prigogine, Hildebrand, Eyring, Flory, Gibbs, and DiMarzio in which multidimensional lattice representations and refined statistical mechanical approaches have been used are the basis for much of today's understanding of the thermodynamic behavior of polymers and their solutions. In this work the lattice energy of a polymer is defined in terms of reduced molecular parameters, and it is assumed that all polymers with the same functional form for their lattice energies will be in corresponding states. A reduced second order transition temperature is defined relative to a characteristic temperature T* = sϵ*/2kv* c, where the molecular parameters refer to the properties of the repeating segments of the polymer chain. Equations are derived that express the effects of molecular weight, plasticization, degree of crosslinking, and copolymerization on the second order (i.e., glass) transition temperature. In their limits, the equations are shown to reduce in form to equations derivable from free volume theory. They are also used to analyze successfully a variety of glass transition temperature data available in the literature on homogeneous uncrosslinked and crosslinked polymers, plasticized polymers, and random copolymers.
Depression of the glass transition temperature of poly(methyl methacrylate) by plasticizers: Conformity with free volume theory
Authors: Kalachandra S. , Turner D. T.
Published: April 2003

Mixtures of poly(methyl methacrylate) (PMMA) and plasticizer were made by γ‐irradiation of mixtures of methyl methacrylate with diethyl phthalate or with dioctyl phthalate. The glass transition temperature Tg was determined by differential scanning calorimetry. Plots of Tg versus volume fraction of PMMA were found to conform to the simple free volume theory of Kelley and Bueche, using physical property values either reported in the literature or else calculated by Bondi's procedures.
The effect of network chain‐length distribution, specifically bimodality, on strain‐induced crystallization
Authors: Sun C.‐C. , Mark J. E.
Published: April 2003

Polyurethane elastomers were prepared from a series of poly(ethylene oxide) samples by end‐linking the chains into “model” trifunctional networks. The molecular weight Mc between crosslinks in such networks is simply the number‐average molecular weight Mn of the precursor polymer. End‐linking samples separately gave networks with unimodal distributions of network chain lengths, whereas end‐linking mixtures of two samples having very different values of Mn gave bimodal distributions with average values of Mc equal to the average value of Mn for the two samples. Stress‐strain isotherms in elongation were obtained for these networks, both unswollen and swollen to various extents. Strain‐induced crystallization was manifested in elastic properties that changed significantly with changes in temperature. Swelling has more complicated effects, since it causes deformation of the network chains as well as melting of some of the crystallites. Comparisons among stress‐strain isotherms at constant Mc indicate that bimodality facilitates strain‐induced crystallization.
Counterion and solvent effects on the dilute solution viscosity of polystyrene ionomers
Authors: Agarwal Pawan K. , Garner Richard T. , Graessley William W.
Published: April 2003

We present an analysis of data on the intrinsic viscosity [η] of sulfo‐polystyrene ionomers in several solvents for a variety of sulfonation levels and counterions. For solvents of low dielectric constant, 2 < ε < 18, [η] decreases from the base polymer value [η]0 with increasing substitution level. This behavior was attributed to intramolecular association of ionic dipoles. The ratio [η]/[η]0 was found to depend on a single reduced variable αAαSx, where x is the fractional substitution, αA depends only on the counterion, and αS ∝ ε−1 depends only on the solvent. For solvents of high dielectric constant, 36 < ε < 47, [η] increases approximately as x3, and counterion effects are small. This behavior was attributed to ionic dissociation, giving rise to a polyelectrolyte effect. Implications of the low ε results are discussed in relation to association‐induced gelation behavior and possible generalizations of the reduced variables approach.
Hole transport of trans‐1,2‐biscarbazolylcyclobutane‐doped poly(bisphenol A carbonate) film
Authors: Tsutsumi Naoto , Yamamoto Masahide , Nishijima Yasunori
Published: April 2003

The hole transport of trans‐1,2‐biscarbazolylcyclobutane (CB) doped poly(bisphenol A carbonate) (PC) film has been investigated in the CB concentration range of 3.8 × 10−4 mol cm−3 (12 wt%) to 1.6 × 10−3 mol cm−3 (51 wt%). The hole mobility increased drastically with increasing CB concentration. The hole mobility was analyzed by a random hopping model. The localization radius ρ0 of the CB/PC system was 1.9 Å, which is larger than that obtained for the N‐isopropyl‐carbazole‐doped PC system. This suggests that the larger localization radius of the CB/PC system is related to the larger spatial extent of the CB molecule. The highest hole mobility of 2.9 × 10−6 cm2 V−1 s−1 was obtained when the CB concentration was 1.6 × 10−3 mol cm−3 (51 wt%) at E = 1.6 × 105 V cm−1 and T = 298 K. This mobility is about 10 times higher than that of poly(N‐vinylcarbazole) (PVCz). The activation energy of hole mobility for the CB/PC system decreased with increasing CB concentration and was 0.31 eV at 51 wt% of CB, which is lower than the 0.45 eV for PVCz. The low activation energy for the CB/PC system is ascribed to the absence of an excimer‐forming site that works as a multiple‐trapping site for hole carriers.