bluuebunny/crossref_metadata_2025_split huggingface dataset:
Intrinsic viscosities of four homopolymers and one copolymer in nonpolar solvents. I. Effect of correlations of molecular orientations
Authors: Filiatrault Danielle , Phuong‐Nguyen H. , Delmas Geneviève 
Published: April 2003

AbstractIntrinsic viscosities [η] of four homopolymers, polyisobutylene (PIB), polypentene‐1 (PP‐1), polypentenamer (PPmer), and polydimethylsiloxane (PDMS), and of an ethylene‐propylene copolymer containing 81% ethylene (81% E) have been measured at 25°C in seven linear alkanes ranging from n‐C6 to n‐C16 and three highly branched alkanes, 2,2,4‐trimethylpentane, 2,2,4,6,6‐pentamethylheptane, and 2,2,4,4,6,8,8‐heptamethylnonane. Correlation of molecular orientations (CMO) in the polymers was investigated. The difference Δ[η] = [η](lin) − [η](br) is used as a test of CMO with the supporting assumption that CMO lowers the free energy and the destruction of CMO raises it. The positive value of Δ[η], which varies from 20% to 40% for PPmer and 81% E, is indicative of orientational order in these two polymers. The negative value of Δ[η] for PDMS results from the disordering of linear alkanes by the nonordered PDMS. δ[η] is near zero for PP‐1 and small for PIB implying that these two polymers are indifferent to solvent molecular shape. The variation of [η] with alkane chain length of the linear alkanes gives additional information about size and solvent quality. The dependence is small for ordered polymers due to the short range of CMO. [η] diminishes rapidly with n for PDMS probably because of the increased difference of cohesive energy between polymer and solvent. The dependence is small for PIB but very large for PP‐1. The much better quality of small‐molecule solvents for PP‐1 may be an indication of a helicoidal conformation of this polymer in solution.
Effect of junction constraints on rubber elasticity in multiaxial states of stress
Authors: Erman Burak 
Published: April 2003

AbstractThe strains obtained in an amorphous polymer network subject to multiaxial states of stress are calculated according to a recent molecular theory which takes account of constraints on junctions in real networks. Experimental measurements for biaxial states of stress, for pure shear superposed on tension, and for combined torsion and simple extension, are seen to compare favorably with the predictions of the theory.
An ESR study of polyisobutylene radicals produced by γ‐irradiation at 77 K
Authors: Hori Yasurō , Kashiwabara Hisatsugu 
Published: April 2003

AbstractAn electron spin resonance (ESR) study has been made of radicals trapped in polyisobutylene irradiated at 77 K. It is concluded that only the C(Me)2CH radical remains after heat treatment above 213 K. This radical shows a very sharp doublet ESR spectrum with hyperfine splitting of about 2.2 mT. A broad doublet ESR spectrum observed without warming, which was previously assigned as C(Me)2CHis explained as a mixture of a doublet and a triplet due to the C(Me)2CH and
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radicals. γ‐irradiation at 77 K produces these major radical components and other carbon radicals as minor species. It has also been found that a conversion of other radicals into C(Me)2CHoccurs without decay on annealing below 183 K. Heating in the range 183–213 K causes both conversion and decay of the radicals. On annealing above 213 K, only decay occurs. The ESR spectra of polyisobutylene radicals are easily saturated by microwave power even at 1.6 μW. The mechanism of radiolysis for polyisobutylene is briefly discussed.
Glass transition temperature and heat capacity of heterotacticlike PMMA
Authors: Fernandez‐Martin F. , Fernandez‐Pierola I. , Horta Arturo 
Published: April 2003

AbstractThe glass transition temperature and heat capacity have been determined by differential scanning calorimetry on samples of heterotacticlike monodisperse poly(methyl methacrylate) (PMMA). The nuclear magnetic resonace spectra of these samples reveal that they contain a larger percentage of mr triads (ca. 51%) than atactic polymers and that their microstructure may be predominantly stereoregular because of an abundance of mrrr sequences. We combine our Tg values with data from the literature for PMMAs of other tacticities, in order to analyze the correlation of Tg with tacticity. In this analysis, we consider PMMA as a steric copolymer formed by mm, mr, and rr triads.
The laser‐raman spectrum and a normal‐coordinate analysis of isotactic poly(tertiary butyl acrylate)
Authors: Aylward N. N. , Ti S. S. 
Published: April 2003

AbstractThe coincidence of many bands in the Raman and infrared spectra of isotactic poly(tertiary butyl acrylate) and the crystallographic identity period suggests that it may be treated as a 31 helix whose line group is isomorphous with the factor group C3. A normal‐coordinate analysis of a possible helical 31 conformation allows many of the bands to be provisionally assigned and the potential‐energy distribution to be calculated.
Use of quantum chemistry relations in cationic polymerization: A critical examination
Authors: Bunel C. , Marechal E. 
Published: April 2003

AbstractThe temperature dependence of the reactivity ratio r2 (subscript 2 for styrene) is reported for 1‐and 2‐vinyl naphthalenes, 4‐halogeno‐1‐vinyl naphthalenes, 2‐ and 3‐vinyl phenanthrenes, and o‐methylstyrene. The monomers are classified with respect to In (1/r2) and ΔH # and ΔS# (the differences in activation parameters for homopropagation and crosspropagation). It is shown that the reaction is entropically controlled. It appears that there is no correlation between stabilization energy (ΔE)rs and ΔH# and that the correlation with In(1/r2) is only apparent. The origin of this lack of correlation is analyzed and a new index of reactivity is proposed; its correlation with ΔH# is quite satisfying.
A study of the PE‐PTFE system. I. IR and NMR measurements
Authors: Nagarajan S. , Stachurski Z. H. 
Published: April 2003

AbstractPolyethylene‐polytetrafluoroethylene blends have been prepared by sintering at a temperature of 200°C and various times. Detailed description of the preparation of these samples is given. IR optical and NMR line‐broadening properties of these samples have been measured. The results indicate interaction between the two highly crystalline polymers on the molecular level. The properties of the sintered samples are compared with a mechanical mixture (not sintered) of the two polymers, and the deviations from the law of simple mixtures are interpreted in terms of molecular interactions between the constituent phases.
Dynamic birefringence studies of high‐density polyethylene
Authors: Cembrola Robert J. , Kyu Thein , Suehiro Shoji , Kawai Hiromichi , Stein Richard S. 
Published: April 2003

AbstractA rheo‐optical investigation has been carried out on a sample of high‐density polyethylene (HDPE) in an attempt to examine the nature of the α‐relaxation mechanism. Dynamic mechanical and bi‐refringence behavior was measured over the frequency range of 0.008‐4.3 Hz and temperature range −40 to 100°C. The dynamic mechanical and birefringence data were reduced to a reference temperature of 50°C by a combination of horizontal and vertical superposition. The significance of the vertical shift factor has been discussed extensively in previous papers and is not dealt with here. An Arrhenius plot was made of the log of the horizontal shift factor versus reciprocal temperature for the mechanical and optical data. The mechanical data exhibited three distinct regions, the slopes of which led to activation energies of 70, 90, and 150 kJ mol−1. The temperature at which these dispersions occurred suggested the observation of the β, α1, and α2 relaxation processes. The optical data contained two distinct regions from which activation energies of 55 and 95 kJ mol−1 were obtained. The high‐temperature α2 process was not observed in the Arrhenius plot; however, a maximum in K′ and a change in sign of K″ probably reflects a contribution from the α2 relaxation mechanism.
Effects of high‐pressure CO2 on the glass transition temperature and mechanical properties of polystyrene
Authors: Wang Wen‐Chou V. , Kramer Edward J. , Sachse Wolfgang H. 
Published: April 2003

AbstractHydrostatic pressure usually increases the glass transition temperature Tg of a polymer glass by decreasing its free volume; if the pressurizing environment is soluble in the polymer, however, one might expect an initial decrease in Tg with pressure as the polymer is plasticized by the environment. Just such a minimum in the Tg of polystyrene (PS) is observed as the pressure of CO2 gas is increased over the range 0.1–105 MPa from both ultrasonic (1 MHz) measurements of Young's modulus E and static measurements of the creep compliance J. A time‐temperature‐pressure superposition law is obeyed by PS which allows a master curve for the compliance to be constructed and shift factors to be determined. A master curve for E is then obtained by using the Boltzmann superposition principle. The compliance J reaches a maximum, and E and Tg reach minima, at a CO2 pressure of ca. 20 MPa at both 34 and 45°C, which are above the critical temperature (31°C) of CO2. At the minimum, Tg is 41 at 45°C and 36 at 34°C, the larger depression at 34°C evidently corresponding to the higher solubility of CO2 at the lower temperature. The plasticization effect due to CO2 can be isolated by subtracting the effect of hydrostatic pressure alone from the experimental data. The results leave no doubt that at high pressures CO2 gas is a severe plasticizer for polystyrene.
Some evidence against the existence of the liquid‐liquid transition. I. Transitions or dispersions: A quantitative explanation of one torsional braid log decrement peak
Authors: Plazek Donald J. 
Published: April 2003

AbstractSome of the history of the proposed liquid‐liquid transitions Tll and T′ll that have been reported to exist above the glass transition temperature Tg and the role played by the torsional braid analyzer are outlined. Confusion has been created by the failure to clearly distinguish such kinetic phenomena as viscoelastic and dielectric loss processes from thermodynamic transitions. It is shown quantitatively how the log decrement of an oscillating system can exhibit one more peak than is found in the loss tangent–temperature curve of a viscoelastic liquid.
Some evidence against the existence of the liquid‐liquid transition. II. Properties of and measurements with a torsional braid analyzer
Authors: Plazek Donald J. , Gu Guo‐Fang 
Published: April 2003

AbstractA torsional braid analyzer (TBA) has been constructed for an investigation into the behavior of this instrument. An explanation was desired for the presence of the proposed second liquid‐liquid transition T′ll peak in the log decrement–temperature curve of a low‐molecular‐weight polystyrene whose loss tangent increases monotonically as a function of increasing temperature at constant frequency. The response of the TBA was studied as a function of amplitude of oscillation, the nature of the braid, the braid tension, frequency, and the nature of the impregnant. All of the braids examined were shown to be extremely nonlinear in their response. Two peaks in the damping of the composite system as a function of temperature are attributed to the interaction between the impregnant properties and the nonlinear response of the glass fiber braid.
Some evidence against the existence of the liquid‐liquid transition. IV. The temperature dependence of shear viscosity
Authors: Orbon Stephen J. , Plazek Donald J. 
Published: April 2003

AbstractThe viscosity data available for four anionically polymerized polystyrenes ranging in molecular weight from 1100 to 47,000 for the temperature range Tg to Tg + 100°C have been fitted by computer programs to both the Vogel, Fulcher, Tamman, and Hesse (VFTH) equation and to two optimum intersecting Arrhenius equations. The intersection point has been interpreted as a manifestation of a liquid‐liquid transition. The fits to the VFTH equation were in every case found to be far superior. Systematic deviations of the residuals were observed for the best Arrhenius fits which indicate the lack of any validity for such a representation of the data.
Assignment of an anomalous peak in the brillouin spectrum of oriented polymer films
Authors: Cavanaugh D. B. , Wang C. H. 
Published: April 2003

AbstractThe origin of a previously unassigned peak in the Brillouin spectrum of an oriented polymer film has been clarified. This peak is shown to be due to backscattering from a quasitransverse acoustic phonon from the reflected laser beam. Studies of this peak are expected to provide the information concerning the birefringence effect of the oriented film.
Refinement of linear polymer crystal structures determined from electron diffraction data
Authors: Moss Barbara , Dorset Douglas L. 
Published: April 2003

AbstractThe reliability of linear polymer structures determined by using electron diffraction data is investigated. The results of n‐beam dynamical calculations and kinematic calculations which take account of crystal bending are compared with experimental structure factors for five published structures. In specific cases, both dynamical scattering and crystal bending effects are found to be important. Finally, guidelines are given for obtaining electron diffraction data which are optimal for structure solution.
Epitaxial morphologies of polyoxymethylene. II. Deposition energetics on alkali halide (001) surfaces
Authors: Balik C. M. , Tripathy S. K. , Hopfinger A. J. 
Published: April 2003

AbstractMolecular mechanics energy calculations have been used to assess the relative affinities that an iodobenzene solvent molecule and a segment of a polyoxymethylene chain have for five different alkali halide (001) surfaces. Dispersive‐repulsive and coulombic contributions to the interaction energy have been included. The calculated interaction deposition energy correlates well with the nucleation density of rodlike epitaxial crystals formed on these substrates in epitaxial crystallization experiments from solution. Substrates which have a higher preference for solvent (LiF and NaF) than for polymer exhibit relatively low polymer nucleation densities. As the degree of solvent preference decreases, and polymer preference increases, higher nucleation densities are observed (KCI and KI). These results suggest that preferential solvent adsorption may account for the low nucleation densities observed on some substrates in polymer epitaxial crystallization experiments from solution.
Stress relaxation in styrene‐butadiene‐styrene block copolymers containing unattached linear polybutadiene and styrene‐butadiene diblocks
Authors: Kamykowski Gregory W. , Ferry John D. , Fetters L. J. 
Published: April 2003

AbstractStress relaxation has been studied in networks of styrene‐butadiene‐styrene triblock copolymers with spherical styrene domain structure containing 0.10 weight fraction of unattached linear polybutadiene (Mw = 389,000) or styrene‐butadiene diblocks with very long butadiene segments (M = 225,000 or 510,000). The stretch ratio (uniaxial extension) was usually 1.15 and the temperature ranged from −20 to +20°C. The contribution of the linear polybutadiene species to relaxation was essentially the same in two triblock networks with very different butadiene block lengths, as expected if the configurational rearrangements are dominated by reptation. In the diblock‐triblock mixtures, in which the diblock butadiene segments are free at one end but anchored at the other and therefore incapable of reptation, there was no contribution to relaxation from the dangling butadiene segments of the diblock component; this would be expected if there are no relaxation mechanisms alternative to reptation for these very long semiattached species within the experimental time scale.
Crystallization kinetics of syndiotactic polypropylene
Authors: Miller Robert L. , Seeley Evelyn G. 
Published: April 2003

AbstractMelting‐point and spherulite growth rate measurements for a sample of syndiotactic polypropylene (S = 0.716 and η = 0.356) were analyzed for the parameters characterizing crystal formation and growth: Tm = 159 ± 2°C, σe = 47 erg cm −2, σ = 4.4 erg cm−2, and q = 5.6 kcal per mole of folds. The q and σe values place syndiotactic polypropylene in the group of “unhindered” polymers. Failure of the isotactic‐polypropylene spherulite growth rate data to follow current theories of crystal growth precluded a comparison of crystal parameters of the two stereoisomers. At comparable degrees of supercooling, the absolute growth rates for the two forms are of the same order of magnitude and exhibit one or more crossover(s) in relative position.
Crystallization under stress: A theory of fibrillar crystallization
Authors: Smith K. J. 
Published: April 2003

AbstractA theory of crystallization in stretched polymer networks is developed. In it, four principal features are incorporated: (i) crosslinks are displaced by growing crystallites, (ii) network chains are constrained to positions compatible with fixed sample shape and volume, (iii) some network chains remain amorphous, and (iv) the relative direction of a chain through a crystallite may not be the same for all chains. The derived network force exhibits a V or U shape with changing temperature in the crystallization zone that is a close replica of the behavior of gutta percha networks. Postulates of fibrillar‐lamellar transitions are not introduced into the calculations.
Concentrated solutions of polydisperse rodlike polymers in the isotropic and lyotropic liquid‐crystalline phases. I. The effects of molecular length distribution on phase behavior
Authors: Moscicki J. K. , Williams G. 
Published: April 2003

AbstractThe earlier calculations of Moscicki and Williams of the phase behavior of rodlike macromolecules in solution incorporating a Gaussian distribution of rod lengths have been extended to include, in addition to a “basic” Gaussian distribution, a small amount of high‐molecular‐weight species which are characterized by a δ‐function or “box‐function” distribution. It is shown that C*p, the concentration of polymer at which the biphasic material (isotropic plus anisotropic phase) first appears may be substantially lowered in comparison with that for the system comprising only the basic distribution. The volume fraction ΦA of anisotropic phase, the compositions of the two phases, and the distribution of species between the phases are calculated for a range of polymer concentration which spans the isotropic, biphasic, and anisotropic phase and, among several features obtained, it is shown that the high‐molecular‐weight species are essentially responsible for the initial formation of anisotropic phase in the biphasic system. The results of the calculations have important implications for the interpretation of published dielectric relaxation data for polyalkylisocyanates in solution at high concentration and for published shear‐flow viscosity data for polyalkylisocyanates and poly(p‐benzamide) in solution at high concentration and these are discussed in some detail.
Phase transitions and structural properties of a thermotropic polyester
Authors: Kyotani Mutsumasa , Kanetsuna Hisaaki 
Published: April 2003

AbstractThe phase transition behavior and the structural properties of a thermotropic polyester, poly‐(chloro‐1,4‐phenylene‐trans‐1,4‐cyclohexanedicarboxylate), were studied by differential scanning calorimetry, x‐ray diffraction, polarized‐light microscopy, and electron microscopy. The polyester shows two first‐order transitions in heating, i.e., a crystal‐crystal transition and a crystal‐liquid‐crystal transition at 190–220 and 300–330°C, respectively. The texture in the liquid‐crystalline phase is very similar to that of nematic low‐molecular‐weight materials. Oriented films of the polyester can be obtained from the liquid‐crystalline state. Many fibrils occur in a fractured lateral surface of the film. Bandlike structures 50–100 nm wide were observed in surfaces of both oriented and unoriented films. The direction of the polymer chain axis is almost perpendicular to that of band elongation. In the oriented film, the band structures are perpendicular to the direction of orientation.
Structure and side‐chain interactions in poly(δ‐N‐carbobenzoxy L‐ornithine)
Authors: Sasaki Shintaro , Ban Hiroshi , Uematsu Ichitaro 
Published: April 2003

AbstractTwo crystal modifications are found in α‐helical poly(δ‐N‐carbobenzoxy L‐ornithine). In films as cast, the two‐dimensional unit cell is pseudohexagonal and contains two chains. This form transforms irreversibly into a pseudotetragonal form at about 140°C. A second‐order transition associated with the onset of the side‐chain motion is observed at about 30°C for the bulk sample (by dilatometry) and for the crystalline phase (by x‐ray diffraction). The dielectric behavior of the side‐chain dispersion suggests that the side chains interact with one another. The temperature dependence of the infrared absorbance due to the NH stretching vibration reveals that about half the side chains are associated via hydrogen bonds at room temperature and become dissociated at higher temperature. The enthalpy and the entropy of the hydrogen bond formation is estimated to be ΔH = −5.0 ± 0.5 kcal mol−1 and ΔS = −15 ± 1 e.u. mol−1.
Reversible isopentane‐induced depression of carbon dioxide permeation through polycarbonate
Authors: Chern R. T. , Koros W. J. , Hopfenberg H. B. , Stannett V. T. 
Published: April 2003

AbstractPermeability data are reported for carbon dioxide in Lexan polycarbonate at 35°C. Measurements were made for both pure carbon dioxide and for a mixed feed consisting of carbon dioxide with a 117.8‐torr (0.155‐atm) Partial pressure of isopentane. The effects of varying upstream CO2 driving pressure from 1 up to 20 atm were studied. The permeability to CO2 is reduced significantly in the presence of isopentane; however, the fractional depression of the CO2 permeability due to the isopentane at low driving pressures is much more significant than at high CO2 driving pressures. The well‐known pressure dependence of carbon dioxide permeabilities in glassy polymers, therefore, is largely diminished by introducing isopentane to the pure carbon dioxide feed. These observations are consistent with a model for transport in glassy polymers which explains the observed trends in terms of competition between the two penetrants for microvoid sorption sites existing in the non‐equilibrium glassy polymer. Exclusion of carbon dioxide from microvoid sorption sites by the more condensable isopentane preempts transport through the microvoid regions, resulting in the observed depression of the CO2 permeability.
Poly(vinylidene fluoride)‐γFe2O3 magnetic composites
Authors: Reich S. , Goldberg E. P. 
Published: April 2003

AbstractMagnetic metal‐polymer composites have been prepared by thermolysis of a metal carbonyl Fe(CO5) in poly(vinylidene fluoride). These composites comprise ca. 100‐Å‐diam iron‐oxide, γFe2O3, ferrimagnetic particles dispersed in the polymeric matrix. Small‐angle x‐ray studies show that these particles have a radius of gyration in the range 63–315 Å. The composites were prepared with up to ca. 20 wt % iron and were crosslinked, as evidenced by insolubility. Electron diffraction indicating the formation of some FeF2 suggests metal‐fluorine interaction during formation of the composite.