bluuebunny/crossref_metadata_2025 huggingface dataset:
The solution and transport of gases in poly(N‐butyl methacrylate) in the glass transition region. I. Absorption‐desorption measurements
Authors: Stern S. A. , Vakil U. M. , Mauze G. R.
Published: April 2003

Solubility coefficients, S, and diffusion coefficients, D, have been determined for ethane and n‐butane in poly(n‐butyl methacrylate) (PnBMA) by the microbalance technique in the temperature range from −14 to 50°C, which encompasses the glass transition of the polymer (22–35°C). S and D for ethane were found to be independent of penetrant pressure and concentration at all temperatures studied No transition to “dual‐mode” sorption behavior, as reported for a number of penetrants in glassy polymers, was observed with ethane, even at the lowest experimental temperature. Plots of log S and log D versus 1‐T, the reciprocal absolute temperature, were linear for the ethane‐PnBMA system and did not exhibit discontinuities in the glass transition region. The above results suggest that the same mechanism of solution and transport of ethane in PnBMA is operative both above and below the glass transition of the polymer under the experimental conditions. This behavior is attributed to the low “excess” free volume of glassy PnBMA, as indicated by the small difference between the coefficients of thermal expansion of this polymer in its rubbery and glassy states. Possible conditions for the appearance of dual‐mode gas sorption are discussed. A similar study with the n‐butane‐PnBMA system showed that the polymer was plasticized by the penetrant below 20°C, due to the higher solubility of n‐butane compared with that of ethane in PnBMA.
The effect of soft‐segment length and concentration on phase separation in segmented polyurethanes
Authors: Petrović Zoran S. , Javni Ivan
Published: April 2003

Three series of polyurethanes, based on three polyols, diphenylmethane diisocyanate (MDI), and three chain extenders were synthesized. Polypropylene glycol (PPG) soft‐segment length (MW 1000, 2000, and 3000), soft‐segment concentration (30%, 50%, and 70%), and the type of chain extender (ethylene glycol, butane diol, and hexane diol) were varied and their effect on the amount of phase separation studied. Methods for assessing phase separation quantitatively, based on shifts of the glass transition temperature Tg and the enthalpy jump at the glass transition were tested. It was shown that they give incorrect results, especially with PPG 1000 as the soft segment. Dependence of the soft segment Tg on the polyol length was explained by the “network effect.” True phase mixing was found only with PPG 1000 series at low soft‐segment concentration, whereas, no clear indication of the phase mixing with PPG 2000 and PPG 3000 based polyurethanes was observed.
The hard elasticity of polypropylene and its blends with polyethylene
Authors: Du Qiangguo , Wang Lihui
Published: April 2003

Hard elastic monofilaments from polypropylene (PP) and its blends with polyethylene (PE) have been studied. Filaments with sharply different degrees of hard elasticity have been obtained by the same melt‐spinning process from three types of PP resin with almost the same isotacticity, molecular weight, and melt index and from blends of one of the PP resin with PE or high‐molecular weight PP (HMPP). With addition of a small amount of HDPE or HMPP to the parent PP resin, the hard elasticity of the filaments is increased significantly. Filaments with high hard elasticity can be prepared from PP resins of blends which show a relatively slow spherulitic growth rate. It is argued that the increased hard elasticity is due to row lamellae in PP fibers containing more adjacent folded chains and fewer tie molecules between lamellae and chain entanglements in the amorphous phase.
A mathematical model for stress‐driven diffusion in polymers
Authors: Cox Robert W. , Cohen Donald S.
Published: April 2003

A model for case II diffusion into polymers is presented. The addition of stress terms to the Fickian flux is used to produce the characteristics progressive front. The stress in turn obeys a concentration‐dependent evolution equation. The model equations are analyzed in the limit of small diffusivity for the problem of penetration into a semiinfinite medium. Provided that the coefficient functions obey two monotonicity conditions, the solvent concentration profile is shown to have a steep front that progresses into the medium. The formulas governing the progression of the front are developed. After the front decays away, the long time behavior of the solution is shown to be a similarity solution as in Fickian diffusion. Two techniques for approximating the solvent concentration and the front position are presented. The first approximation method is a series expansion; formulas are given for the initial speed and deceleration of the front. The second approximation method uses a portion of the long time similarity solution to represent the short time solution behind the front.
The effect of morphology on sorption and transport of carbon dioxide in poly(4,4'‐oxydiphenylene pyromellitimide)
Authors: Okamoto Ken‐Ichi , Tanaka Kazuhiro , Yokoshi Osamu , Kita Hidetoshi
Published: April 2003

Sorption and transport of carbon dioxide were investigated for poly(4,4'‐oxydiphenylene‐pyromellitimide) films (PI‐1, PI‐2, and PI‐3) imidized at 160, 200, and 400°C, respectively, as well as for a chemically identical commercial polyimide film, Kapton‐H. The solubility, permeability, and diffusion coefficients (S, P, and
\[ \overline D \]
, respectively) at 80°C and 20 atm in PI‐3 were 67, 25, and 37%, respectively, as large as those in PI‐2. These significant reductions are attributed to a higher degree of segmental aggregation in PI‐3 caused by a 1.7% increase in the density (d) as compared with PI‐2. The differences in S, P,
\[ \overline D \]
, and d between PI‐3 and Kapton‐H were rather small as compared with those between PI‐3 and PI‐2, suggesting that the in‐plane orientation has a minor effect on the sorption and transport in Kapton‐H as compared with the aggregation. Influence of the morphology on the dual‐mode sorption and transport parameters was also investigated. With increasing density, the Langmuir capacity constant and the diffusion coefficients for the Henry's law and Langmuir populations decreased by higher rates than the Henry's law solubility constant, being contrary to the results reported for a typical semicrystalline glassy polymer, polyethylene terephthalate. This may suggest that the nonaggregated or less‐aggregated regions taking an important part in the sorption and transport are denser for the sample having a higher overall density.
Influence of a neutral surface on polymer molecules in the vicinity of the surface
Authors: Fitzgibbon Denise R. , McCullough R. L.
Published: April 2003

Monte Carlo simulations based on the rotational isomeric model are used to investigate the influence of a neutral surface on the structural and thermodynamic descriptors of polymethylene chains on and in the vicinity of the surface. For large chains, the results of the simulations are replicated by a properly scaled distribution based on a random walk with absorbing barriers. Accordingly, the affects noted for the trial polymethylene system may be extended to other molecules.

The perturbations in the geometry of the chain were confined to the components of the various descriptors perpendicular to the surface; the radial components were unaffected by the neutral surfaces. The perturbations induced by the neutral surfaces extend to chains whose origins were within about $\[ 10\left\langle {s_x \left( \infty \right)^2 } \right\rangle ^{1/2} \]$, where $\[ \left\langle {s_x \left( \infty \right)^2 } \right\rangle ^{1/2} \]$ is the perpendicular component of the mean square radius of gyration of an unperturbed chain.

In contrast, the average bond conformation, the associated internal energy, and the variance of the internal energy distribution are unaffected by a neutral surface. The major thermodynamic effect is manifest through the entropy arising from the reductions in accessible chain configurations due to the neutral barrier.
Chain structure and entanglement
Authors: Wu Souheng
Published: April 2003

It is shown that the entanglement junction may be modeled as a binary hooking contact of Kuhn nodes between two chains. The entanglement behavior is thus determined by chain tortuosity and given by Nv = (1/β)C, where Nv is the number of real or virtual skeletal bonds in an entanglement strand, C∞ is the characteristic ratio, α = 2 is the number of hooks involved at an entanglement junction, and β = 1/3 is the fraction of binary hooking configurations out of all possible configurations at a binary nodal contact. In other words, we have Nv = 3C, which is verified experimentally for 44 polymers, covering a wide variety of skeletal, pendant, and stereoisomeric (tacticity) structures. Since C∞ may be estimated by group additivity, the present equation may be used to predict the entanglement behavior from chemical structure.
Effect of length of side chains on the optical configuration parameter of poly(n‐alkyl acrylate) networks
Authors: Ilavský M. , Saiz E. , Riande E.
Published: April 2003

The effect of the length of side chains on the optical configuration parameter Δa of poly(n‐alkyl acrylate) networks was theoretically studied using the valence optical scheme (VOS). The theoretical calculations suggest that Δa should be negative, and its absolute value should increase as the side‐chain length increases. Moreover, a positive temperature dependence is also predicted. By comparing theoretical and experimental results, it was found that the valence optical scheme gives a good qualitative interpretation of the side‐chain effects on the birefringence of the stretched networks. However, the method fails to give a quantitative description of Δa, presumably because strong intermolecular interactions enhance the polarizability along the chains. The fact that the difference between theoretical and experimental values of Δa decreases with increasing side‐chain length suggests that flexible long chains act as a diluent reducing intermolecular interactions that enhance Δa.
Dielectric properties of bisphenol‐a epoxy resins
Authors: Sheppard Norman F. , Senturia Stephen D.
Published: April 2003

The α‐relaxation process of seven commercial diglycidyl ether of bisphenol‐A (DGEBA) epoxy resins of varying molecular weights, without hardener, was characterized by measuring the frequency and temperature dependence of the complex permittivity, (ϵast;). The temperature dependences of the frequency of maximum dipole loss ƒmax and the ionic conductivity σ are non‐Arrhenius and can be described by the Williams‐Landel‐Ferry (WLF) equation. The frequency dependence of the molecular relaxation process is described by the Kohlrausch‐Williams‐Watts (KWW) relaxation function. The WLF C1 parameter and the KWW β parameter, describing the temperature and frequency dependences, respectively, vary systematically with the molecular weight of the resin. These results are discussed in the context of recent theories of the glass transition.
Diffusion of linear polyisoprene molecules into polyisoprene networks
Authors: Gent A. N. , Kaang S. Y.
Published: April 2003

Diffusion and equilibrium absorption of polyisoprene liquids into crosslinked samples of cis‐polyisoprene (natural rubber) have been studied by direct observation of volume swelling. Natural rubber was crosslinked in the form of fine threads, about 40 ± 20 μm in diameter, using a gaseous reaction with SO2 and H2S (the Peachey process). An optical microscope was used to observe the relatively rapid absorption of linear high‐molecular‐weight polyisoprene liquids by these fine threads. From the kinetics of absorption, values of the self‐diffusion coefficient Ds of polyisoprene were estimated. They ranged from 10−16 m2/s to 10−12 m2/s, depending upon molecular weight, and varied with molecular weight approximately as M−2 over the entire range employed, from 1,000 to 60,000 g/mol, i.e., both above and below the entanglement molecular weight. Amounts of polymer absorbed at equilibrium varied widely, depending upon the degree of crosslinking of the host material and the molecular weight of the absorbing liquid. They were in reasonable agreement in all cases with simple swelling theory, with the heat of mixing equated to zero.
Study of ferroelectric transitions of vinylidene fluoride–trifluoroethylene copolymers
Authors: Faria R. M. , Latour M.
Published: April 2003

Thermally stimulated depolarization (TSD) measurements with superimposed “piezoelectric noise” allow us to identify the ferroelectric‐to‐paraelectric phase transition in vinylidene fluoride–trifluoroethylene (VDF/TrFE) copolymers with different molar ratios. In addition, a new transition which did not change the ferroelectric features of the material has also been detected. Long relaxation processes always accompany these transitions. By the initial‐rise method we calculated the activation energies for these relaxations as 0.73 eV for the ferroelectric‐to‐paraelectric transition and 0.33 eV for the ferroelectric‐to‐ferroelectric one.
Permeation of carbon dioxide through homogeneous and asymmetric polysulfone membranes
Authors: Sada E. , Kumazawa H. , Xu P.
Published: April 2003

To confirm the validity of the working assumption that a thin dense skin layer in an asymmetric membrane can be essentially replaced by a thick homogeneous dense membrane, both homogeneous and asymmetric polysulfone membranes were prepared by solvent casting, and the permeation behavior of carbon dioxide through these two types of membranes was investigated. The pressure dependence of the mean permeability coefficient through an asymmetric polysulfone membrane is apparently very similar to that through a homogeneous dense membrane, following the dual mode mobility model driven by gradients of chemical potential. The dense skin layer in the asymmetric membrane can be simulated approximately by a homogeneous dense membrane from the point of view of gas sorption and diffusion.
Metal‐catalyzed oxidation of poly(α‐methylstyrene) during surface‐enhanced Raman scattering
Authors: Boerio F. J. , Tsai W. H. , Montaudo Giorgio
Published: April 2003

Surface‐enhanced Raman scattering (SERS) was used to characterize thin films of poly(α‐methylstyrene) (PMS) spin‐coated onto silver island films supported by glass substrates. At laser powers of a few tens of milliwatts, SERS spectra of thin films of PMS (about 100 Å) were weak, and only the bands near 1010 and 1040 cm−1 were observed. At laser powers of about 100 mW, additional bands characteristic of PMS were observed near 720 and 1610 cm−1. However, oxidative degradation of the PMS films to form graphite‐like substances was also observed at the higher laser powers. When the thickness of the PMS films was increased to several hundred angstroms, degradation of the films was inhibited, but the intensity of the Raman scattering remained constant, indicating that the observed SERS was an interfacial rather than bulk effect. Degradation during SERS experiments was also inhibited by overcoating PMS films with much thicker films of poly(4‐styrene sulfonate) (PSS). Scattering from the PSS overlayers was not observed as long as the thickness of the PMS films was greater than several tens of angstroms, again showing that the SERS was an interfacial effect. Oxidative degradation of the PMS films was also inhibited by adding a few percent of the antioxidant 2,6‐di‐tert‐butyl‐4‐methylphenol to the polymer. Bands related to sulfite contaminants adsorbed onto the silver island films were observed near 640 and 940 cm−1. These bands disappeared when PSS, but not PMS, was spin‐coated onto the SERS substrates, indicating a strong interaction between PSS and silver.
Birefringence, compliance, and viscoelasticity of poly(ethylene terephthalate) fibers
Authors: Northolt M. G. , Roos A. , Kampschreur J. H.
Published: April 2003

The experimental relation between birefringence and dynamic compliance has been determined for a wide range of poly(ethylene terephthalate) fibers. This relation is explained by two complementary versions of the series aggregate model. The classical series aggregate model provides a satisfactory interpretation of the data for the low‐oriented fibers. A model developed earlier for aramid fibers explains the data for the well‐oriented fibers. By monitoring the dynamic compliance during creep and stress relaxation of well‐oriented fibers it is shown that these phenomena are caused by shear relaxation, resulting in a progressive contraction of the chain orientation distribution.
Crystallization oftrans‐1,4‐polyisoprene and of hydrochlorinated segmented block copolymer derivatives from solution
Authors: Corrigan Joseph P. , Zemel Irina S. , Woodward Arthur E.
Published: April 2003

Crystallization oftrans‐1,4‐polyisoprene from the mixed solvent pair hexane/2‐pentanone was carried out and the effects on the morphology of seeding and the solvent composition were studied. α‐TPI lamellae obtained by crystallization from a single solvent, hexane, at 20°C and by mixed‐solvent crystallization at 40°C were characterized by DSC, FTIR, and suspension epoxidation/C‐13 NMR. Crystalline stem lengths of 14.5 and 18 and a fold length of 10 monomer units were found. Segmented block copolymers were prepared by reaction of TPI lamellae in acetone suspension with HCl at −7°C. These products were dissolved in 2‐pentanone and precipitated at 0°C. A lamellar morphology, the details of which depend on the TPI block length, was observed by SEM; both preparations showed sharp endotherms; and the FTIR was characteristic of a combination of amorphous TPI, amorphous hydrochlorinated TPI, and of either the β crystalline form or both the α and β forms for TPI depending on the sample.
Studies of poly(vinylidene fluoride)/poly(vinyl pyrrolidone) blends. I. Thermal transitions by differential scanning calorimetry
Authors: Alfonso Giovanni Carlo , Turturro Antonio , Pizzoli Maria , Scandola Mariastella , Ceccorulli Giuseppina
Published: April 2003

Thermal measurements were carried out to investigate the macrostructure of as‐cast poly(vinylidene fluoride) (PVDF)/poly(vinyl pyrrolidone) (PVP) blends. At high PVP content, above about 70 wt.%, the two components form a homogeneously mixed amorphous phase whose Tg varies with composition. Crystals are formed upon casting mixtures richer in PVDF; these systems exhibit complex thermal behavior that cannot be justified by a simple two‐phase model. DSC measurements above room temperature on semicrystalline blends show, in addition to the melting of PVDF crystals at temperatures that decrease on increasing PVP content, a glass transition at about 80°C, independent of composition. Experimental results strongly support the hypothesis that an interphase, composed of essentially undiluted noncrystalline PVDF, is always associated with the lamellar crystals.
A phenomenological description of large deformations in polymeric glasses (polycarbonate)
Authors: Koenen J. A. , Heise B. , Kilian H.‐G.
Published: April 2003

A new description of the quasistatic deformation of polymeric glasses is presented. The stress‐strain energy of a glass is defined to comprise two components: a “solid term,” which controls the low‐strain range of deformation, and a “conformational term” proportional to the first strain invariant. By introducing internal variables in terms of classical irreversible thermodynamics, the stress‐strain behavior and the thermoelastic properties of polycarbonate are fairly well described over the whole range of accessible strains. The necking phenomenon is interpreted as a “constrained strain‐induced phase transition” (“one‐way phase transition”). A new version of a Clapeyron‐Clausius equation is derived. Its application yields a new understanding of the temperature dependence of yielding of cold‐drawn polycarbonate. The typical phenomena of a first‐order transition, discussed in the special form of a “one‐way phase transition,” have been fully identified experimentally (by microscopy, stretching‐microcalorimetry, simple extension, and birefringence). Sharp phase boundaries appear just when the new phase is nucleated. The transition then proceeds under a constant force as demanded by thermodynamics. The stress‐strain behavior is shown to be uniquely dependent on temperature at temperatures below the glass‐transition range. General consequences of the phenomenological treatment are discussed.
A model of environmental craze growth in polymers
Authors: Brown H. R.
Published: April 2003

A model of environmental craze growth has been developed based on the customary meniscus (or Rayleigh‐Taylor) instability model of craze propagation but allowing for the possibility that environmental plasticization may cause the active layer of material adjacent to the craze to be of significant thickness with respect to the fibril spacing. Initially, as the active layer thickness increases, the fibril growth rate increases at constant fibril spacing, but eventually the fibril spacing comes to be controlled only by the active layer thickness and not by the surface tension and stress. This model of craze growth has been coupled to a model of stress‐enhanced case II diffusion that is itself based on the Thomas‐Windle model. Two main regimes of craze thickness growth are distinguished. In one the craze growth rate is controlled by the velocity of the diffusion front, the meniscus instability growth rate is assumed to be relatively slow, so that a significant plasticized active layer exists whose thickness assures that the meniscus instability front travels at the same speed as the diffusion front. In the other regime the propagation of the craze front is sufficiently fast that it also forms the diffusion front, so the growth rate is controlled by a combination of the two processes: diffusion and meniscus instability.
Characterization of thermal diffusion in polymer solutions by thermal field‐flow fractionation: Dependence on polymer and solvent parameters
Authors: Schimpf Martin E. , Giddings J. Calvin
Published: April 2003

The thermal diffusion coefficient DT has been obtained for 17 polymer‐solvent combinations, each of them spanning a range of polymer molecular weights, using thermal field‐flow fractionation. The polymers examined include polystyrene, poly(alpha‐methyl)styrene, polymethylmethacrylate, and polysioprene. The solvents include benzene, toluene, ethylbenzene, tetrahydrofuran, methylethylketone, ethylacetate, and cyclohexane. Although DT was confirmed as essentially independent of polymer molecular weight, it was found to vary substantially with the chemical composition of polymer and solvent. The results were used to evaluate several thermal diffusion theories; the agreement with theory was generally found to be unsatisfactory. Attempts were then made to correlate the measured thermal diffusion coefficients with various physicochemical parameters of the polymers and solvent. A good correlation was found in which DT increases with the thermal conductivity difference of the polymer and solvent and varies inversely with the activation energy of viscous flow of the solvent.
Mechanical relaxations in trans‐1,4‐polyisoprene crystals
Authors: Anandakumaran K. , Manley R. St. John
Published: April 2003

Dynamic mechanical relaxation spectra were obtained for solution‐grown crystals of trans‐1,4‐polyisoprene (TPI) in the α and β form. For single crystal mats three relaxations were observed. The highest temperature relaxation peak was characterized as due to the crystalline regions, whereas the intermediate peak was assigned to the primary amorphous relaxation which originates from the fold regions. The nature of the amorphous regions was elucidated by examining the effect of epoxidation on the lamellar fold surface. For an epoxidized single crystal mat, the intermediate relaxation maximum shifted to a higher temperature which corresponds to the glass transition of the almost completely epoxidized TPI. These results are discussed in terms of the fold structure of the TPI single crystals.
A Flory–Huggins thermodynamic approach for predicting sorption equilibrium in ternary polymer systems
Authors: Campos Agustin , Gavara Rafael , Tejero Roberto , Gomez Clara , Celda Bernardo
Published: April 2003

The Flory–Huggins theory as modified by Pouchlý has been applied to calculate preferential (λ) and total (Y) sorption coefficients for a ternary polymer system. The ternary interaction function (ϕ1ϕ2ϕ3GT(u1, ϕ3)) is described as the product of three independent binary functions. This expression allows prediction of λ and Y from binary interaction parameters χ, χ, g, g, and g12(ϕ10). Three ternary polymer systems are used to check the validity of the expression. Moreover for polymer systems in which the parameters g and/or g are unknown, a procedure to evaluate them has been developed and verified on systems for which sufficient experimental information is available.
Vibrational spectroscopy of the oxidation of polyethylene. I. Fourier self‐deconvolution of the carbonyl absorption
Authors: Maddams W. F. , Parker S. F.
Published: April 2003

Fourier self‐deconvolution of the carbonyl peak present in the infrared spectrum of oxidized polyethylene has successfully resolved the peak into its components. Three strong bands at 1713, 1719, and 1723 cm−1, together with a number of weaker features, are detected. In agreement with previous work, the 1719 and 1723 cm−1 bands are assigned to saturated ketones and saturated carboxylic acids, respectively. A new band is also observed at 1697 cm−1. The relative amounts of the components differ between high‐density, linear low‐density, and low‐density polyethylene. The 1697 cm−1 band is very dependent on the type of polyethylene; it is strong in high‐density, weak in linear low‐density, and very weak in low‐density polyethylene.
Nucleation‐controlled growth in polyethylene single crystals: Growth and shape of {100} sectors
Authors: Toda Akihiko
Published: April 2003

The nucleation rate and propagation rate of steps on the {100} faces of polyethylene crystals have been determined. For single crystals, under conditions where the width of the {100} sectors remains constant during growth, it is confirmed that the growth is in regime I or the crossover region between regime I and II. In {110} twinned crystals, the {100} sectors are well developed and the width increases linearly with time; therefore, the growth in the twins must be in regime II. It is shown that the differing growth regimes of {100} faces in single crystals and twins allow the independent determination of the nucleation rate and the propagation rate of steps. The nucleation rate and propagation rate of steps on the {100} faces were determined from measurements of the constant width of the {100} faces in single crystals and the growth rate of the {100} faces in single crystals and twins. The observed rates show abnormal dependence on supercooling and concentration. The results are attributed to a weaker dependence of the constant width of {100} sectors on supercooling and concentration than predicted.
Compatibility of poly(vinyl chloride) with polyalkyleneoxides. II. Poly(propylene oxide) and poly(tetramethylene oxide)
Authors: Margaritis A. G. , Kalfoglou N. K.
Published: April 2003

This study [Part II of a series dealing with the compatibility of polyalkyleneoxides with poly(vinyl chloride)] examines blends of PVC with poly(propylene oxide) (PPrO) and poly(tetra‐methylene oxide) (PTMO), covering the entire composition range. Morphological, dynamic mechanical and thermal properties investigated indicate that PVC/PPrO blends are incompatible, whereas the PVC/PTMO system shows miscibility in the melt. For this polyblend and at high polyether compositions where the Hoffman–Weeks analysis can be applied, Tm equilibrium data allow the determination of the thermodynamic interaction parameter, χ12 = −0.15. Experimental compatibility data of all polyether‐PVC pairs investigated in Parts I and II are also used to test various blend miscibility prediction schemes, using solubility parameter theory and recent theory on copolymer‐copolymer miscibility.
Phase transitions in lattice solutions of semiflexible chains of finite length
Authors: Ronca G.
Published: April 2003

Lattice solutions of finite chains with reduced flexibility are shown to form phase equilibria characterized by broad phase gaps of width increasing with molecular weight. DiMarzio's treatment of excluded volume also gives predictions on bulk transitions. Both in solution and in the bulk, the orientational order parameter and fraction of straight configurations of the anisotropic phase at the transition increase with chain length. Calculations on infinite chain systems fail to detect phase equilibrium in solution at different concentrations.
Morphology and cation local structure in a blend of copper‐neutralized carboxy‐terminated polybutadiene and poly(styrene‐co‐4‐vinylpyridine)
Authors: Register Richard A. , Sen Ashish , Weiss Robert A. , Li Chi , Cooper Stuart
Published: April 2003

Carboxy‐terminated polybutadiene neutralized with Cu2+ (CuPBD) and its blend with poly(styrene‐co‐4‐vinylpyridine) (SVP) were examined by differential scanning calorimetry (DSC), transmission electron microscopy (TEM), small‐angle x‐ray scattering (SAXS), and extended x‐ray absorption fine structure (EXAFS) spectroscopy. The DSC results indicate that in the blend substantial mixing occurs in the CuPBD‐rich phase, although complete miscibility is not achieved, and the SVP‐rich phase remains relatively pure. The TEM micrographs indicate that the morphology, while irregular, is reasonably described as bicontinuous, with a domain size of order 100 nm. The SAXS patterns show that the ionic aggregates present in CuPBD are destroyed upon blending, which is interpreted as being due to steric hindrances between ionic groups coordinated to vinylpyridine nitrogens. The EXAFS radial structure function of the blend exhibits a marked decrease in the Cu‐Cu peak in comparison with CuPBD, indicating a change in local structure upon blending. The results indicate that some of the SVP is miscible with CuPBD owing to complexation between the pendant pyridine groups and the Cu2+ ions, which disrupts the ionic aggregates. However, the two materials are not fully miscible, leading to a rather coarse two‐phase morphology.
A study of polymer blends by nonradiative energy transfer fluorescence spectroscopy
Authors: Zhao Yue , Lévesque Jocelyne , Roberge Pierre C. , Prud'homme Robert E.
Published: April 2003

The nonradiative energy transfer (NRET) method has been used to study the miscibility of polymer blends in the solid state. This can be done by labeling the polymers with fluorescence donor and acceptor chromophores. The efficiency of energy transfer, which reveals the interpenetration of the chains, is measured by following changes in the fluorescence intensity ratio of the donor and acceptor as a function of the concentration of the polymer mixture and by comparison with reference values corresponding to totally miscible and totally immiscible systems. It is shown that the reference ratio corresponding to the absence of energy transfer must be determined by using donor‐labeled and acceptor‐labeled polymer films, instead of making measurements in chromophore solutions in organic solvents, as has usually been done. It is also shown that fluorescence quenching is important in such studies, since it can lead to variations of the fluorescence intensity ratio by more than an order of magnitude; this factor varies with blend concentration and is particularly sensitive to the presence of halogen atoms. The NRET technique has been applied to several PVC/CPVC binary blends and to PCL/PVC/CPVC ternary blends in which PVC and CPVC were labeled by naphthalene and anthracene, respectively [PCL is poly(ε‐caprolactone), PVC is poly(vinyl chloride), and CPVC is chlorinated PVC]. For binary blends, the measured intensity ratios indicate the immiscibility of PVC with CPVC, although there is nonnegligible energy transfer between the two phases. For ternary blends, the intensity ratios indicate that the addition of up to 40 wt % of PCL to the immiscible PVC/CPVC binary system leads to the formation of two coexisting PCL/PVC and PCL/CPVC phases.
X‐ray diffraction by thermotropic main‐chain polymers with side groups. I. rigid polyesters
Authors: Chin Hui H. , Azároff Leonid V. , Lenz Robert W.
Published: April 2003

Thermotropic poly(sulfonyl hydroquinone terephthalate) with either H or CH3 in the lateral substituent was aligned by drawing from nematic melts. Virtually identical x‐ray intensity distributions were recorded consisting of “disks” of intensity periodically spaced along the meridian and concentric rings of intensity lying in the equatorial plane of reciprocal space. They correspond to what is expected for the hexagonal packing of parallel periodic chains that are randomly displaced along the chain axes. Using interactive graphics, appropriate molecular models were deduced in conformity with the observed diffraction intensities.
Small‐angle scattering of polarized light. II. experiments with isotropic spheres
Authors: Desbordes M. , Meeten G. H. , Navard P.
Published: April 2003

New experimental measurements are reported of small‐angle polarized and depolarized light scattering from almost monodisperse isotropic, spherical particle, polystyrene latexes. The shape and intensity distribution of the scattering patterns is shown to compare closely with the calculated patterns based on the exact Mie scattering theory from a single sphere.
Crystalline phases of electrically conductive poly(p‐phenylene vinylene)
Authors: Masse Michael A. , Schlenoff Joseph B. , Karasz Frank E. , Thomas Edwin L.
Published: April 2003

Poly(p‐phenylene vinylene) (PPV) undergoes a first‐order crystal‐crystal phase transition when chemically doped with AsF5, SbF5, or H2SO4 or electrochemically oxidized with ClO‐4 as the counterion. These structures have been observed using wide‐angle x‐ray diffraction. Doping with these agents does not disrupt the original orientation of the PPV crystallites. The crystalline phases obtained with all dopants employed here are similar in character, indicating a closely related family of electrically conductive structures having orthorhombic symmetry. An electrically conductive phase consisting of layers of polymer chains separated by a layer of the chemical dopant is proposed.
Swelling behavior of an aromatic polyimide
Authors: Gattiglia E. , Russell T. P.
Published: April 2003

The swelling behavior of poly(N, N'‐bisphenoxyphenylpyromellitimide) (PMDA‐ODA) using dimethylsulfoxide DMSO and N‐methylpyrollidinone NMP was investigated by gravimetric means. For PMDA‐ODA samples imidized on a substrate, the weight uptake was found to depend linearly on time over a temperature range from 25 to 150°C. For a given temperature of imidization, the equilibrium swelling concentration was found to be independent of the temperature at which the swelling studies were performed. However, the rate of solvent uptake depended strongly on the swelling temperature, yielding an activation energy of about 50 kJ/mol. In general, increasing the initial imidization temperature caused a decrease in the rate of swelling but did not alter the equilibrium swelling concentration. This swelling behavior resembles Case II diffusion typically seen in glassy polymers with some noteworthy exceptions. In cases, where PMDA‐ODA was imidized in a free‐standing state, no swelling was observed. However, deformation of these isotropic specimens was found to induce substantial swelling.
Modification of transport properties of ion‐exchange membranes VIII. Changes in properties of anion exchange membranes on introduction of hydrophobic groups
Authors: Sata Toshikatsu , Yamamoto Yoshihisa
Published: April 2003

A copolymer membrane composed of 4‐vinylpyridine‐styrene‐divinylbenezene was reacted with long chain alkyl bromides (octyl bromide, dodecyl bromide, and hexadecyl bromide) in order to introduce hydrophobic groups into the anion exchange membrane by the quaternization reaction. The resulting membranes show a marked increased in fixed ion concentration as a result of lowered water content. Although the electrical resistance of the membranes increased slightly, the apparent diffusion coefficient of hydrochloric acid through the membranes decreased markedly. Complete quaternization of the membranes by methyl iodide after reaction with the long‐chain alkyl bromides caused an increase in the water content and in the apparent diffusion coefficient of the acid and a decrease in the current efficiency in electrodialysis of the acid. This is explained by the high water content of the anion exchange membranes quaternized by methyl iodide.
Sorption and partial molar volume of gases in polybutadiene
Authors: Kamiya Yoshinori , Naito Yasutoshi , Mizoguchi Keishin
Published: April 2003

Sorption of He, H2, N2, O2, Ar, CH4, C2H6, and C2H6 in polybutadiene and the dilation of the polymer due to sorption of the gases are investigated over the pressure range 0‐50 atm at 25°C. For CO2 the measurements are made at temperatures ranging from 15 to 80°C. Partial molar volumes of the gases in the polymer are determined. The temperature dependence of partial molar volume is discussed on the basis of the data for CO2. The Flory‐Huggins interaction parameters of CO2, C2H4, and C2H6 are also estimated.
Rheo‐optical properties of polyethylene films in the nonlinear viscoelastic region
Authors: Tanaka Akira , Fukuda Mitsuhiro , Nagai Hiroyuki , Shinohara Masayuki , Onogi Shigeharu
Published: April 2003

A new apparatus was designed to investigate the dynamic viscoelastic properties of solid polymer materials in the nonlinear viscoelastic region. The apparatus was combined with a birefringence apparatus in such a way that birefringence could be measured simultaneously with stress under oscillatory deformation. The nonlinear viscoelastic behavior of bulk‐crystallized high‐density polyethylene films was examined. Nonlinearity of mechanical properties became evident around 30°C, while optical properties became markedly nonlinear around 50°C. The nonlinearity of viscoelastic properties changes very little when the films are swollen with tetrachloroethane. It is proposed that disruption of lamellae to crystallites in the drawing process is one of the most important causes of the nonlinear behavior of high‐density polyethylene films.
Annealing effects of phase I poly(vinylidene fluoride)
Authors: Takase Y. , Scheinbeim J. I. , Newman B. A.
Published: April 2003

The effects of annealing temperatures on stretched poly(vinylidene fluoride) film were systematically studied from the “as‐received” condition up to the melting range (180°C). X‐ray diffraction studies indicate that the annealing process brings about better chain packing and increased crystallite perfection. The elastic modulus and piezoelectric strain and stress constants, d3, and e31, decrease as the annealing temperature Ta increases up to 160°C, while the remanent polarization Pr remains almost constant. Some of these characteritics may be interpreted in terms of a morphological transformation of microfibrils. The values of Pr, d31, and e31 increase dramatically as Ta increases from 160 to 180°C; Pr increases from 56 to 85 mC/m2, d31 from 20.2 to 27.7 pC/N, and e31 from 51.4 to 65.2 mC/m2. As a result, the values of Pr and d31 were the largest recorded from any of the samples used in the present study. e31 showed a value close to the largest one; this usually occurs in unannealed samples. Samples annealed in the melting range also exhibit significantly improved ageing characteristics. The large value of Pr and the small relaxation strength of both the dielectric constant and elastic modulus indicates that the largest crystallinity obtained is approximately 70%.
Mechanical relaxations in polypropylene: A new experimental and theoretical approach
Authors: Jourdan C. , Cavaille J. Y. , Perez J.
Published: April 2003

Accurate dynamic mechanical measurements have been performed on semicrystalline isotactic polypropylene over wide ranges of temperature and frequency. A mechanical model has been used to analyze experimental results in order to separate the behavior of amorphous and crystalline phases. The two main α and β relaxation processes have been analyzed. The β relaxation, related to the glass‐rubber transition of the amorphous fraction, has been studied with the help of a physical model. The behavior is similar to that of a wholly amorphous polymer, with two characteristics: a high rubbery plateau, indicating a crosslinking effect by the crystalline phase, and a strong effect of interfaces in shear strain. Experimental data suggest the α relaxation originates within the crystalline phase and that it can be attributed to diffusion of defects. The amorphous phase plays an important role in this process, because it has to adapt itself by cooperative movements to respect the compatibility of deformations of the two phases. The formalism developed here rationalizes experimental results obtained with samples having different thermal histories.
Thermal behavior of poly(1,8‐nonadiyne) and its cross‐polymerized product
Authors: Butera R. J. , Lando J. B.
Published: April 2003

The diacetylene macromonomer poly(1,8‐nonadiyne) was investigated using differential scanning calorimetry in an effort to characterize the solid‐state cross‐polymerization reaction which occurs when this material is exposed to high‐energy radiation. Specifically, DSC was used as a means to monitor the degree of conversion in the crystalline regions of partially cross‐polymerized samples. Results from the thermal analysis of the virgin macromonomer indicate that little, if any, thermally induced reaction occurs during the DSC heating scans. Heat of fusion data were used to estimate the degree of conversion in partially cross‐polymerized samples. The apparent maximum degree of conversion in the crystalline regions of this macromonomer system was found to be 78% using this method. The actual maximum conversion for the system is probably somewhat lower.
Crystallization of segmented trans‐1,4‐polyisoprene/epoxidized trans‐1,4‐polyisoprene block copolymers from solution
Authors: S. Zemel Irina , P. Corrigan Joseph , E. Woodward Arthur
Published: April 2003

The crystallization of segmented block copolymers of trans‐1,4‐polyisoprene (TPI)/expoxidized TPI from solution was investigated. One preparation with an average TPI block length of 14.5 and an average epoxidized TPI block length of 10 was crystallized from 2‐pentanol at 20°C, 2‐octanol at 20°C, and 2‐pentanone at 0°C. A second preparation with an average TPI block length of 18 and the same average epoxidized TPI block length was crystallized from 2‐octanol at 20°C and 2‐pentanone at 0°C. The crystallization products were expoxidized in suspension a second time and then characterized by carbon‐13 solution NMR to determine the average noncrystalline traverse length and the average crystalline stem length. The crystallized products were also studied by scanning electron microscopy, Fourier transform infrared spectroscopy, and differential scanning calorimetry to determine the morphology, the crystal form and crystallinity, and the melting point, respectively. The average noncrystalline traverse length was found to be highly dependent on the crystallization conditions and the crystalline stem length of the parent TPI lamellas; the composition of these traverses is discussed.
Sorption and transport of carbon dioxide in a polyimide from 3,3′4,4′‐biphenyltetracarboxylic dianhydride and 4,4′‐diaminodiphenyl sulfone
Authors: Okamoto Ken‐Ichi , Tanaka Kazuhiro , Kita Hidetoshi , Nakamura Asumaru , Kusuki Yoshihiro
Published: April 2003

CO2 sorption and transport were investigated for the polyimide prepared from 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA) and 4,4′‐diaminodiphenyl sulfone (DDS). The morphology of films did not change on annealing above the glass transition temperature and remained amorphous unlike the polyimide prepared from BPDA and 4,4′‐oxydianilline (ODA). This seems to be due to the strong hindrance to rotation of the sulfonyl linkage. Sorption and transport data were analyzed according to the dual‐mode model. Solubility, diffusion, and permeability coefficients at 20 atm and 80°C for BPDA‐DDS polyimide were substantially equal between as‐cast and annealed films and were 1.7, 2.2, and 3.7 times greater, respectively, than for the as‐cast films of the BPDA‐ODA polyimide. The higher solubility was due to larger values of the Henry's law solubility constant kD, Langmuir capacity constant C, and the Langmuir affinity constant b. The sorption and transport properties were compared with those for amorphous glassy aromatic polymers including other polyimides. The relation of k, C, b, and the diffusion coefficients in the Henry's law population and the Langmuir population (DD and DH) with other properties of the polymers were discussed. Values DD and DH for BPDA‐DDS polyimide were much larger than expected from the estimated free‐volume fraction.
Coefficient seebeck et méanismes de conduction dans les polymères (PPP) electroactifs dopés par implantation ionique
Authors: Moliton A. , Duroux J. L. , Ratier B.
Published: April 2003

A study of the Seebeck coefficient has shown that doping of polyparaphenylene by ion implantation makes it possible to obtain an electronically doped semiconductor at low energy: n‐type with alkali metal ions and p‐type with halide ions. At the highest energies (E > 100 keV) the p‐type conductivity is due to the creation of defects by irradiation. Generally the semiconductor obtained is degenerate with a Seebeck coefficient close to that obtained by chemical doping. Study of the mechanisms of conduction suggests plots of log σ = (T−l/n); the greater n is, the better is the agreement between the experimental curve and theory. Representation of the conductivity is proposed according to Mott's theories, which are applicable to amorphous semiconductors and involve several conduction processes in the temperature space. For the variable‐range‐hopping (VRH) mechanism at low temperature, two parameters, α−1 (representing the spatial separation of hopping sites) and N(EF) (the density of states at the Fermi Level) are obtained.
Elastic modulus of poly(ethylene oxide) determined from the Raman longitudinal acoustic mode
Authors: Song Kigook , Krimm Samuel
Published: April 2003

The chain modulus of poly(ethylene oxide) is determined by the Raman longitudinal acoustic mode method with the aid of a normal coordinate analysis and found to be 1.3 × 1011 dyn/cm2. Our normal mode calculations provide a clear basis for explaining the discrepancy between chain moduli determined from Raman and x‐ray experiments. They show that the uncorrected Raman modulus of helical polymers reflects the presence of interchain interactions and therefore should not be taken as the correct elastic modulus of a single chain.
Glass transition temperature versus conversion relationships for thermosetting polymers
Authors: Pascault J. P. , Williams R. J. J.
Published: April 2003

Owing to enthalpy relaxation, values of the glass transition temperature (Tg) for partially reacted polymers may depend on the thermal history of samples and the heating rate used for measurements. Use of theoretical relations between Tg and the extent of reaction (x) of a thermoset must take this fact into account. The original DiBenedetto equation has been reevaluated as a convenient constitutive equation for expressing Tg versus x. An extension of Couchman's approach for the expression of the compositional variation of Tg enabled us to derive the same functionality as given by the DiBenedetto equation. Thus, the DiBenedetto equation may be regarded as based on entropic considerations applied to a model of the thermosetting polymer consisting of a random mixture of a fully reacted network with the initial monomers in an amount which depends on the particular conversion level. These two equations have been applied with success to different diepoxy‐diamine copolymers.