bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetics of microstructure rearrangement during annealing of cold‐drawn isotactic polypropylene
Authors: Babajko Suzanne , Schultz J. M.
Published: April 2003

The microstructure of polypropylene, annealed after cold drawing to an oriented state, was examined using density measurements and small‐ and wide‐angle x‐ray scattering (SAXS and WAXS) techniques. SAXS patterns were obtained after annealing (in an oil bath), and during annealing (of samples annealed in a furnace placed directly in the x‐ray beam). Data, for isothermal annealing, showed an increase in SAXS intensity, in crystal perfection, and in density over the observed time range, but no change in long spacing during the same period. Long spacing, SAXS intensity, and density were all strongly dependent upon annealing temperature, increasing at higher temperatures. Upon annealing the elastic modulus and yield strength dropped below the as‐drawn values in an immeasurably short time, and did not appear to change thereafter during the time range examined. The decrease was more marked for higher‐temperature annealing. The kinetics of the micro‐structural changes are compared qualitatively to the predictions of nucleation and growth theory and of spinodal decomposition. The defects in the microstructure are considered as the “solute molecules” of the spinodal model. The experimental results do not agree neatly with either model. However, a nonequilibrium thermodynamic approach appears to be the more promising. It is suggested that the kinetics of mechanical property change may be due to different rates of migration for different defect species.
The crystal structure of the alternating copolymer of hexafluoroisobutylene and vinylidene fluoride
Authors: Weinhold S. , Litt M. H. , Lando J. B.
Published: April 2003

The crystal structure of the alternating copolymer of hexafluoroisobutylene and vinylidene fluoride, P(HFIB/VF2), was determined using x‐ray diffraction techniques. Oriented specimens of the copolymer were produced by drawing melt‐pressed film at 300°C. The unit cell of P(HFIB/VF2) is orthorhombic with dimensions at a = 1.064, b = 1.837, and c = 0.783 nm. The chain conformation is a 21 helix with an approximate trans‐trans‐gauche‐gauche backbone dihedral‐angle sequence. Severe intrachain steric crowding exists; as a consequence, the chain is quite rigid and some of the backbone bond angles are highly extended. The unit cell contains four such chains packed according to the symmetry of space group Iba2. Neighboring chains in a crystal are mechanically interlocked; in combination with the rigidity of the chains, this is the basis for the superior mechanical properties of the copolymer compared to PTFE. A structure containing up to 20‐30% of head‐to‐head residues was found to be statistically indistinguishable from a completely head‐to‐tail structure.
A neutron scattering analysis: How does the conformation in polyethylene crystals reflect that in the melt?
Authors: Sadler D. M. , Harris R.
Published: April 2003

Neutron scattering data for melt‐crystallized polyethylene have been analyzed in order to clarify to what extent the chain folding is randomly reentrant. No attempt has been made to specify the molecular conformation in every detail, and the emphasis is on distinguishing between different classes of conformation. The most random folding corresponded to a model where the folding is imposed solely by the criterion of the chain segments moving the least possible distance during the crystallization process (a “freezing‐in” model). This has been shown not to be compatible with published data. For this model analytic calculations are possible based on the projection of a three‐dimensional Gaussian distribution onto a plane. A subunit model is then proposed which requires substantial local rearrangement of the chain as it folds during crystallization, but where the distribution of the subunits within the whole molecule is imposed by the preexisting Gaussian chain of the melt. Arguments based on space filling considerations are invoked, with the postulate of a surface structure which is neither crystalline nor truly amorphous. Anything approaching a random switchboard model (e.g., the freezing‐in model which we consider) is contrary to both space filling considerations and to the comparison of observed and calculated neutron scattering. The analytical calculation which was performed for the freezing‐in model was employed so as to simplify calculations for the subunit model. For scattering intensities over a wide range of scattering angle it is deduced that only the structure within the subunit need be considered. Numerical computer calculations involving only a small number of stems were then carried out for a number of different subunit structures, and some general features are noted which restrict the type of model which can explain the data. As in previously published analyses, a very high proportion of adjacent folds is not compatible with the results. A row model for the stems within a molecule can achieve good agreement, either with straight rows or with a certain amount of “stagger” incorporated. Up to about 40% of the folds could be adjacent. Models based on two‐dimensional random walks did not give good agreement.
High‐resolution dark‐field imaging in epoxy and polyimide systems
Authors: Oberlin A. , Ayache J. , Oberlin M. , Guigon M.
Published: April 2003

The feasibility of molecular imaging in polymers by electron microscopy is discussed. The tilted dark‐field method is specifically chosen for studying ultramicrotome thin sections. One system studied here is bisphenol‐A diglycidyl ether epoxide monomer (DGEBA) amine cured either by dicyandiamine or by diaminodiphenyl sulfone under various conditions. The second sample is a polyimide prepared from maleic anhydride and diaminophenyl methane. The distribution of the molecules is consistent with the random‐coil model when neither etching nor strains are applied. Bisphenol‐A groups distributed at random in the polymer are imaged in DGEBA as units 10 Å long and 5 Å wide, whereas larger isometric diffracting domains (10–15 Å) are imaged in polyimides.
Thermal expansion of ultradrawn polystyrene
Authors: Wang Li‐Hui , Choy C. L. , Porter Roger S.
Published: April 2003

Measurements on the linear thermal expansivities α∥ and α⊥ parallel and perpendicular to the extrusion direction, respectively, have been carried out between −160 and 30°C for atactic polystyrene (aPS) with extrusion ratio 1 ≤λ≤ 15 and isotactic polystyrene (iPS) with 1 ≤λ≤ 7.5. For both aPS and iPS, α∥ decreases sharply with increasing λ whereas α⊥ shows only a slight increase. Below λ = 5 the anisotropy α⊥/α∥ is nearly the same for both, but α⊥/α∥ for iPS becomes much larger at higher λ. This is accompanied by an abrupt rise in crystallinity and probably results from the increase in the number and tautness of intercrystalline tie molecules. The birefringences of aPS and iPS increase with λ and have nearly the same values for λ < 5. At higher λ, however, there is a sharp rise in the birefringence of iPS which is probably associated with the sudden increase in crystallinity. With an aggregate model, the chain orientation function for aPS calculated from thermal expansivity is found to be in reasonable agreement with the corresponding value obtained from birefringence.
Spin‐lattice relaxation in the rotating frame in solutions of poly(2,6‐dimethyl‐1,4‐phenylene oxide)
Authors: Jones Alan Anthony , Shea Francis P.
Published: April 2003

Methyl‐proton spin‐lattice relaxation times in the rotating frame T1ρ are reported for 10‐wt % solutions of poly(2,6‐dimethyl‐1,4‐phenylene oxide) in CDCl3. These measurements were made as a function of molecular weight and at two Larmor frequencies: 30 and 90 MHz. The T1ρs are substantially shorter than the spin‐lattice relaxation times T1, indicating conditions far from the extreme narrowing limit. However, the observed values of T1ρ correspond very well to predictions from an earlier interpretation of T1s. The interpretation was based on four motions likely in this polymer: overall rotatory diffusion, segmental motion, phenyl group rotation, and methyl group rotation. All parameters in the interpretation such as correlation times had been set in the previous interpretation of T1s, leaving none to be adjusted to account for the T1ρs. Nevertheless, agreement between the predicted and observed T1ρs is excellent; this is apparently the first such quantitative interpretation of T1ρs in a dissolved polymer far from the extreme narrowing limit. This agreement at high molecular weight points to the adequacy of the description of local motion from high frequencies to relatively low frequencies and to the improved utility of T1ρ data versus T2 data as a check of low‐frequency contributions to the spectral density. The agreement at lower molecular weights indicates that the description of long‐range motions is sufficient though clearly oversimplified by the omission of the Rouse–Zimm modes.
Studies of magnetic resonance phenomena in polymers. I. The effects of free volume and segmental mobility on the motion of nitroxide spin probes and labels in poly(methyl methacrylate)
Authors: Tsay Fun‐Dow , Hong Su Don , Moacanin Jovan , Gupta Amitava
Published: April 2003

Thin films of spin‐probed and spin‐labeled poly(methyl methacrylate) (PMMA) have been examined by electron spin resonance (ESR) at X‐band frequency (9.2 GHz) and at various temperatures. Direct spectral evidence is presented to indicate that the composite ESR spectra observed in a certain temperature range originate from two states of distinctly different mobility, one with slow motions corresponding to a glassy state and the other with fast motions corresponding to a liquidlike state. The coexistence of these two states at temperatures considerably below the glass transition temperature can be explained as a result of the effect of free volume in a solid polymeric glass.
Vapor‐liquid equilibria for polyisobutylene solutions
Authors: Saeki S. , Holste J. C. , Bonner D. C.
Published: April 2003

Vapor sorption isotherms in binary solutions of polyisobutylene (PIB), (Mη = 4.7 × 106 g/mol) in hydrocarbons (cyclopentane; cyclohexane; n‐heptane; 2,2‐dimethyl butane; and 2,2,4‐trimethyl pentane) and chlorinated methanes [carbon tetrachloride (CCI4) and chloroform (CHCI3)] have been determined at 23.5°C using the piezoelectric sorption method. The polymer‐solvent interaction parameter χ obtained agrees with previously published values determined by using gas‐liquid chromatography and a quartz‐helix vapor sorption apparatus. The Flory theory of corresponding‐states has been applied to the experimental results through the χ parameter and affords a good prediction of the concentration dependence of χ for solutions of chloroform, carbon tetrachloride, n‐heptane, and 2,2‐dimethyl butane in PIB. The experimental values of \documentclass{article}\pagestyle{empty}\begin{document}$ [\partial (a_1 /\psi _1 )/\partial a_1 ]_{T,P} $\end{document} for the PIB solutions are constant over the measured concentration range, for example \documentclass{article}\pagestyle{empty}\begin{document}$ [\partial (a_1 /\psi _1 )/\partial a_1 ]_{T,P} $\end{document} = −4.1 for CCI4, −3.65 for CHCI3, −3.0 for 2,2‐dimethyl butane and n‐heptane, −2.7 for 2,2,4‐trimethyl pentane, −2.7 for cyclohexane, and −1.7 for cyclopentane, where a1 is the solvent activity and ψ1 is the solvent segment fraction. The correlations between the values of \documentclass{article}\pagestyle{empty}\begin{document}$ [\partial (a_1 /\psi _1 )/\partial a_1 ]_{T,P} $\end{document} and the theories of Guggenheim, Miller, Huggins, and Flory are discussed.
Studies on mechanical and swelling behavior of polymer networks on the basis of the scaling concept. 3. The osmotic compressibility of gels
Authors: Zrinyi M. , Horkay F.
Published: April 2003

The osmotic compressibility of chemically crosslinked poly(vinyl acetate) (PVAc) gels in equilibrium with pure diluent has been determined by the method of decreasing equilibrium swelling in different swelling agents. The concentration dependence of the osmotic compressibility has been found to follow a scaling law with an exponent which was greater than that predicted by the mean‐field theory. A comparison has been made between the elastic moduli determined by unidirectional deformation measurements and the compressional moduli obtained from the osmotic compressibility data.
Electrical conduction in composites of a TCNQ anion‐radical salt in a polymer matrix
Authors: Kishimoto Yoshio , Shimotsuma Wataru
Published: April 2003

The conduction behavior of composites of the anion‐radical salt NaTCNQ (sodium 7,7,8,8‐tetracyanoquinodimethanide) in poly(vinyl chloride) plasticized by polyurethane has been studied. TCNQ salt‐polymer composites that have good moldability and flexibility are characterized by molecular or granular dispersion of the TCNQ salt in a polar polymer matrix. The conduction mode changes from one due to molecularly dispersed sites (CMDS) to one due to granularly dispersed sites (CGDS) with increasing NaTCNQ content. In the CMDS region, the predominant conduction is ionic; TCNQ anion‐radicals migrate toward the anode under a dc biasing voltage and a high‐resistivity layer is formed near the cathode. The fixation of TCNQ salt at sites in the polymer matrix is believed to be important for the stabilization of electronic conduction under a dc electric field. In the CGDS region, the conduction is electronic and the current‐voltage characteristics of the composite are nonohmic, which indicates that carrier generation depends on the Poole‐Frenkel effect.
Concentration effects on partitioning of dextrans and serum albumin in porous glass
Authors: Brannon J. H. , Anderson J. L.
Published: April 2003

Partitioning of three dextrans and bovine serum albumin (BSA) in controlled‐pore glass beads was measured by a batch mass balance technique. For all solutes the measured partition coefficient increased with bulk phase concentration, and the relationship appeared to be linear up to 0.05 g/mL for the dextrans. The measured slopes of partition coefficient versus concentration were compared with predictions using a hard‐sphere theory, and while the agreement was tolerable for BSA, the dextran results were much lower than the theory dictated except for very small pores, in which case it was speculated that molecular weight polydispersity resulted in anomalous partitioning of the smaller components.
Nematic and cholesteric thermotropic polyesters with azoxybenzene mesogenic units and flexible spacers in the main chain
Authors: Blumstein A. , Vilasagar S. , Ponrathnam S. , Clough S. B. , Blumstein R. B. , Maret G.
Published: April 2003

Properties of linear polyesters based on azoxybenzene and 2,2′‐methylazoxybenzene moieties with linear, flexible spacers based on mixtures of dodecanedioic acid (DDA) and methyladipic acid (MAA), chiral or racemic, of various compositions (system MAA/DDA‐8 and MAA/DDA‐9, respectively) have been described. Substitution of methyl groups in the 2,2′ or 3,3′ positions of the mesogenic core leads to soluble and relatively low‐melting‐point polyesters. The viscosity law for (MAA/DDA‐9) polyesters in 1,1,2,2 tetrachloroethane gives an exponent 0.76, indicating well‐sol‐vated, coiled chain conformations in dilute solution. Calorimetric data show an increase in isotropization entropy ΔSNI with increasing average length of the spacer. This suggests a nonrandom conformation of the spacer in the nematic melt with a degree of order superior to that of low‐molecular‐weight analogs. X‐ray data obtained with an oriented nematic glass quenched from the nematic melt of DDA‐9 subjected to a magnetic field of 10–12 T also support the extended‐chain model in the nematic phase of DDA‐9. Oriented fibers can be produced by subjecting nematic melts of polyesters 8 and 9 either to magnetic fields of high intensity or to shear fields. The x‐ray data obtained from these fibers also support the extended‐chain model. Cholesteric systems do not orient in the magnetic field of 10–12 T. The study of mesophases of systems 8 and 9 indicates a dramatic influence of the position of the ester group on the stability of the mesophase in the azoxybenzene polyesters. The results are interpreted in terms of geometric factors influencing the colinearity of the mesogenic core and of the extended spacer.
Phase relationships in a ternary solution composed of a solvent and two monodisperse homologous polymers
Authors: Fujita Hiroshi , Teramoto Akio
Published: April 2003

Exact expressions are derived for the spinodal, critical conditions, and separation factor of a ternary solution consisting of a pure solvent and two monodisperse homologous polymers in which the Flory‐Huggins interaction parameter χ depends separately on the concentrations of the polymer components. The results allow one to see the difference from previous expressions obtained with χ depending on the total concentration of the polymer, and are expected to be useful for experimental determination of the Gibbs free energy of ternary solutions.
Effect of molecular entanglements on craze microstructure in glassy polymers
Authors: Donald Athene M. , Kramer Edward J.
Published: April 2003

Thin films of ten glassy polymers are bonded to copper grids and strained in tension to produce crazes, which are then examined in the transmission electron microscope. The average craze fibril extension ratio λ for each polymer is determined from microdensitometer measurements of the mass thickness contrast of the crazes. The extension ratio λ is found to increase approximately linearly with the chain contour length le between entanglements, as determined from melt elasticity measurements of the entanglement molecular weight of these polymers. These results are analyzed by comparing them with λmax, the maximum extension ratio of an entanglement network in which polymer chains neither break nor reptate (i.e., permanent entanglement crosslinks are assumed). The values of λmax are given by le/d where d, the entanglement mesh spacing in the unoriented glass, is computed from d = k(Me)1/2 with k determined either from small‐angle neutron scattering results on isolated chains in the glass or from coil size measurements in dilute solutions of a θ solvent. The craze extension ratios fall somewhat below λmax at low λ but increase to well above λmax for polymers with high le. This comparison suggests a significant contribution due to chain breakage (or reptation) in the higher‐λ crazes of large‐le polymers, which may arise from the higher true stresses in the craze fibrils (which for a given applied stress increase proportionally to λ). The results also imply that a useful way to increase the “brittle” fracture stress and decrease the ductile‐to‐brittle transition temperature of a glassy polymer is to decrease its entanglement contour length le.
Fluorescence depolarization in polymers: The microviscosity of bulk polybutadiene and of solutions in cyclohexane
Authors: Barkowski D. , Mersch W. , Dorfmüller Th.
Published: April 2003

The reorientational relaxation of 9‐cyananthracene fluorescent label molecules has been measured in bulk polybutadiene and solutions with cyclohexane by a fluorescent depolarization technique. The procedure adopted consists in the incorporation of an Arrhenius temperature dependence of the orientational relaxation time in the Perrin equation, thus obviating the necessity of an independent determination of the intrinsic polarization ratio P0 and enabling one to obtain the preexponential factors and the activation energies of the reorientational relaxation times. The most noteworthy result in our view is the validity of the Arrhenius equation for the effective microviscosity as opposed to the validity of the Fulcher–Vogel–Tamann equation with a glass point of T0 = 136 K for the shear viscosity of a polymer solution (90%).
A study of the PE–PTFE system. II. ESCA measurements
Authors: Nagarajan S. , Stachurski Z. H. , Hughes M. E. , Larkins F. P.
Published: April 2003

Samples of polyethylene and polytetrafluorethylene were sintered at 200°C. The samples were cleaved and cut, and the two types of surfaces were studied by ESCA. The possibility of chemical interaction between the two polymers and the formation of a transitional layer is postulated on the basis of the results. A morphological model of the structure of these samples is given.
Single crystals of cellulose IVII: Influence of the cellulose molecular weight
Authors: Buleon A. , Chanzy H. , Froment P.
Published: April 2003

The influence of the degree of polymerization (DP) of cellulose was evaluated in the preparation of micron‐sized cellulose IVII lamellar crystals in order to ascertain whether a regular chain‐folded morphology could develop during their growth. For this purpose, sharp fractions of cellulose acetate were collected by preparative gel permeation chromatography. Aliquots of these fractions were deacetylated and crystallized in dilute solutions containing water, methylamine, and DMSO, and held at 150°C under pressure. Well‐developed cellulose IVII lamellar crystals were obtained with fractions of DP 22–24 whereas higher‐DP material gave polycrystalline aggregates. This behavior indicates that large lamellar crystals of cellulose IVII can be obtained only with unfolded short cellulose chains. The occurrence of chain‐folded crystals with high–DP cellulose samples cannot be demonstrated.
Structural studies of ultrahigh‐modulus polyethylene using nitric acid etching and gel permeation chromatography. II. Influence of polymer molecular weight, draw temperature, and annealing
Authors: Capaccio G. , Ward I. M.
Published: April 2003

The technique of nitric acid etching followed by gel permeation chromatography has been used to determine the crystal length distribution in ultrahigh‐modulus polyethylenes. The crystal length distribution has been studied as a function of draw ratio, polymer molecular weight, processing conditions, and annealing. The results confirm that although there is a considerable broadening of the crystal length distribution on drawing, the majority of crystals have lengths less that 500 Å. There are detailed changes in the length distribution due to changes in draw temperature, molecular weight, and annealing which are not always reflected in corresponding changes in the long period determined from small‐angle x‐ray scattering. Possible reasons for these discrepancies are discussed.
Solution behavior of metal sulfonate ionomers. II. Effects of solvents
Authors: Lundberg R. D. , Phillips R. R.
Published: April 2003

Previous studies on the dilute‐solution behavior of sulfonated ionomers have shown these polymers to exhibit unusual viscosity behavior in mixed solvents of low polarity. These results have been interpreted as arising from specific solvation effects by the solvents with the metal sulfonate groups which persist as ion pairs. The consequences of ion pair interactions and their solvation are exceptional thickening behavior at low polymer levels as compared to unfunctionalized polymers, and anomolous solution viscosities with varying temperature. These studies have now been extended to single‐component solvents which traverse a range of polarities. Using the sodium salt of lightly sulfonated polystyrene (S‐PS) as a model system, the authors found the solution behavior in low‐polarity solvents (tetrahydrofuran) to be consistent with that observed previously for mixed solvents; ion pair interactions predominated. However, in polar solvents such as dimethyl sulfoxide or dimethyl formamide, these polymers behave as classic polyelectrolytes even at sulfonate levels below 2 mol %. The behavior of the S‐PS acids is similar to that observed for the metal salts. To a first approximation these two behaviors, ion pair association and polyelectrolyte behavior, are dependent on solvent polarity. In some cases it is possible to induce polyelectrolyte behavior in a S‐PS/solvent combination exhibiting ion pair interactions by the addition of very low levels of a polar cosolvent, such as water. These results again demonstrate the selectivity of the solvent‐sulfonate interactions.
Effect of substituents in the styrene ring on the dynamic mechanical relaxations of a styrene‐crosslinked unsaturated polyester resin
Authors: Douglas William , Pritchard Geoffrey
Published: April 2003

The dynamic mechanical properties of a series of polyester resins made from a maleic/phthalic anhydride‐based unsaturated polyester crosslinked with each of styrene, 4‐methyl styrene, 4‐ethyl styrene, 4‐n‐butyl styrene, 4‐isopropyl styrene, tertiary butyl styrene, 4‐chlorostyrene, and 3,4‐dichlorostyrene were studied. The order of the α transition temperatures was as expected from that for the homopolymers, except in the case of the chlorostyrenes, for which dipolar interactions with the polyester chain may be important. The styrene bridges appeared to be involved in a steric interaction (and in the case of the chlorostyrenes, a dipolar interaction) with the β relaxing ester species. It is suggested that both the γ and γ′ relaxations involve similar interactions between the matrix and the relaxing moieties. For the 4‐n‐butyl styrene resin, an additional relaxation below −170°C was observed, and is ascribed to relaxation of the n‐butyl group.
Calculation of the nonlinear stress of polymers in oscillatory shear fields
Authors: Helfand Eugene , Pearson Dale S.
Published: April 2003

Complex moduli are calculated for the lowest‐order deviations from linearity of the stress in an oscillatory shear field. The calculations involve solution of an equation, recently proposed by Doi, which goes beyond the “independent alignment approximation” of the Doi‐Edwards theory of polymer dynamics. The new equation incorporates various reptative motions of a polymer in the effective constraining tube induced by entanglements, viz. Brownian motion along the tube and the systematic motion in response to changes in the length of the tube accompanying affine deformation.
Additive moduli for crosslinked epoxies
Authors: Hartmann Bruce , Lee Gilbert
Published: April 2003

Ultrasonic measurements were made on a series of eight crosslinked polyepoxides over the temperature range from 0 to 60°C at a frequency of 2 MHz. From these measurements the bulk (K) and shear (G) moduli were calculated. These data were then analyzed in terms of molecular component properties. Proceeding by analogy with Rao's rule for liquids, the authors found that K is not an additive property but the function U = V(K/ρ)1/2γ is an additive property. Here V is molar volume, ρ is the density, and γ is the Gruneisen parameter (for interchain vibrations). A similar relation was found to hold for shear modulus. In particular, G is not an additive property but W = V(G/ρ)1/2g is an additive property, where g = (1/2α) (∂ InG/∂T)p – 1/2 is the shear analog of the Gruneisen parameter. Using U and W, calculations were made of K and G as functions of temperature for the eight epoxies. These results agree with the measured values within the experimental uncertainty of the measurements.
Distribution spatiale des dommages produits par les ions Kr (1 MeV/amu) et Cl (1 MeV/amu) dans le triacétate de cellulose
Authors: Moliton J. P. , Boutinaud C. , Decossas J. L. , Vareille J. C. , Teyssier J. L. , Delaunay B.
Published: April 2003

Our earlier results on ασ and heavy‐ion‐radiation damage in cellulose triacetate (CTA) are compared with those of previous authors on UV‐and γ‐radiation damage in the same material. Thus the common effects of these different methods of irradiation can be distinguished from those characteristic of the radiation employed. With heavy‐ion radiation the production of stable radicals is accompanied by C—O cleavage. In the case of Kr (1 MeV/amu) ions, the number of free radicals produced is investigated, without distinguishing the species, by using the scavenger technique in the solid phase, combined with UV spectroscopy. On the other hand, C—O cleavage is observed by IR spectroscopy, with its inherent selectivity. A statistical study shows that the experimental curves representative of the evolution of the optical transmittance ratio before and after irradiation L(N) versus the ion fluence N are of exponential type:

where β is a parameter related to the volume damaged by a single ion and, therefore, to the latent track size. The latter is approximated by a cylinder whose height is equal to the range of the ion. For Kr8+ (1.1 MeV/amu) the track length is 21 μ. For each type, damages are localized within a radius of 250 Å for free‐radical yields, 148 Å for cellulosic chain cleavages, 108 Å for deacetylation, and 100 Å for opening of pyrannosic rings. The track length is 14 μ for Cl6+ (1 MeV/amu), while the radius of the cylinder in which free radicals are produced is only 80 Å.
Observations par microscopie électronique de traces d'ions lourds dans le triacétate de cellulose
Authors: Vareille J. C. , Decossas J. L. , Moliton J. P. , Teyssier J. L. , Delaunay B.
Published: April 2003

Tracks of heavy charged particles have been observed in cellulose acetate by conventional electron microscopy (100 kV) and by high voltage microscopy (1, 2 MV). The tracks are formed of successive islets following each other at distances of 70‐150 Å. With the evolution of the diameter of these zones is shown the existence of a highly perturbed cylindrical volume (diameter 400 Å for the case of krypton) corresponding to regions in which free radicals have been created. The different techniques used do not allow observation of the latent track because of the complications of energetic phenomena: the electron beam current density being limited, the contrast is small and hence the resolution is restricted.
Pressure‐volume‐temperature properties of blends of poly(2,6‐dimethyl‐1,4‐phenylene ether) with polystyrene
Authors: Zoller P. , Hoehn H. H.
Published: April 2003

The pressure‐volume‐temperature (PVT) properties of blends of poly(2,6‐dimethyl‐1,4‐phenylene ether) (PPO) with polystyrene (PS) have been studied experimentally in both the glassy and melt states at 0, 20, 40, 50, 60, 80, and 100% PPO content. In all compositions a strong glass transition was observed varying linearly with composition. For all but the 40% PPO composition this was the only transition, indicating molecular compatibility of the components in these blends. The 40% PPO composition showed a very weak second transition near the glass transition of pure PS. A small amount of phase separation may have occurred in this blend. The data for the glassy and melt states were fitted to an empirical equation of state based on the Tait equation. The volume of the melts at constant pressure and temperature showed a virtually linear dependence on composition. Any negative excess volume of mixing compatible with the data would have to be very small, smaller than expected from previous measurements in the glassy state. Various properties relating to the glassy and melt states and to the glass transition were evaluated and are discussed as a function of composition. It was found that most properties of the glasses could not be modeled by simple functions of composition.
Theoretical equation of state of polymer blends: The poly(2,6‐dimethyl‐1,4‐phenylene ether)–polystyrene pair
Authors: Jain R. K. , Simha R. , Zoller Paul
Published: April 2003

A recent theory of multicomponent fluids is applied for the first time to a compatible binary polymer blend. Good accord between the experimental pressure‐volume‐temperature measurements over the whole range of compositions by Zoller and theoretical predictions obtains. In particular, satisfactory predictions of high pressure from low‐pressure information result. From the interplay between experiment and theory, the scaling quantities and thus the characteristic self‐ and cross interaction parameters are derived. The excess volumes are discussed and estimates of excess enthalpies presented. The theory predicts the actual enthalpy of the components or mixtures once the scaling parameters have been determined by means of volume‐temperature data at atmospheric pressure. Enthalpy measurements to test these predictions are highly desirable.
Crystalline order in polyethylene: A 13C NMR CP/MAS solid‐state T1 study
Authors: Axelson D. E.
Published: April 2003

The carbon‐13 spin‐lattice relaxation times T1 of the crystalline components of four solid ethylene‐octene copolymers have been studied as a function of thermal history, branching number, and branching distribution. Slowly cooled samples (1 deg/min from melt to room temperature) exhibited similar or longer T1s with respect to the same sample quench cooled (from the melt into 20°C water). The greater the degree of branching and the more homogeneous the branching distribution, the shorter were the observed crystal lattice T1s. Differences of up to a factor of 3 in T1 were observed for the same sample undergoing the two thermal treatments. Different degrees of branching homogeneity (for the same total number of branches) resulted in differences approaching a factor of 7 for samples with the same thermal history. These variations were attributed to the differing effects of side‐chain disruption of the crystal lattice.
Stress response and energy dissipation in a linear viscoelastic material under periodic triangular strain loading
Authors: Yang Ting Qing , Chen Yu
Published: April 2003

A general equation is derived for the stress response of a linear viscoelastic material to periodic strain excitation at constant strain rates. The energy dissipated in any cycle, especially in a steady‐state loop, is discussed. The results can be used to analyze test results in determining mechanical properties of polymers. A simple Maxwell model and a three‐parameter Maxwell model are used to illustrate the calculation of stress response and energy dissipation under constant‐strain‐rate loading.
Small‐angle x‐ray and neutron scattering studies of amorphous polymer blends
Authors: Russell T. P. , Stein R. S.
Published: April 2003

Dilute mixtures of poly(ε‐caprolactone) (PCL) in poly(vinyl chloride) (PVC), poly(p‐iodostyrene) (PpIS) in polystyrene, and deuterated polystyrene (d‐PS) in protonated poly(o‐chlorostyrene) (PoCIS) were investigated by means of small‐angle x‐ray scattering and small‐angle neutron scattering. The radii of gyration of PCL in PVC and of d‐PS in PoCIS were found to be expanded over the θ values by 50 and 30%, respectively. Values of the second virial coefficient were positive although errors prevented definitive evaluation of the interaction parameter. PpIS was found to aggregate, with both the radius of gyration and molecular weight increasing with concentration. Concentrated mixtures of PCL and PVC were also investigated by using the Debye–Bueche correlation function analysis. Correlation distances indicated good mixing throughout the entire composition range.
Affinity of a hindered phenol antioxidant for reagents in hydrocarbon media: A low‐temperature dielectric relaxation study
Authors: Gilchrist John Le G.
Published: April 2003

Low‐temperature dielectric loss measurements reveal a tendency of 4‐methyl‐2, 6‐di‐tert‐butyl phenol (the antioxidant BHT) to associate with various reagents in hydrocarbon media. The affinity with carbonyl groups appears to be particularly appreciable. It is suggested that this may have a bearing on the antioxidant activity of this type of compound.
NMR spectroscopic, osmometric, and viscometric study of association of syndiotactic poly(methyl methacrylate) in dilute solutions
Authors: Spěváček J. , Schneider B. , Bohdanecký M. , Sikora A.
Published: April 2003

Association of syndiotactic (s) poly(methyl methacrylates) (PMMAs) in toluene, benzene, and acetonitrile has been studied by NMR spectroscopy, osmometry, and viscometry. It was found that in solutions of highly syndiotactic PMMA in toluene, most of the polymer exists in the associated state. Association takes place by means of stereospecific intermolecular and intramolecular interactions of long parallel syndiotactic sequences. The minimum length of syndiotactic sequences necessary for association of s‐PMMA in toluene is 7–8 monomer units. Viscosity data indicate that in dilute solutions the associated structures appear as large formations which do not have the character of compact particles. The formation of the aggregates of PMMA is a relatively slow process. A model of the structure of the aggregates of s‐PMMA in toluene is proposed. As compared with that in toluene, the tendency to aggregation in benzene and acetonitrile is negligible. Integral parameters currently used for the characterization of polymer‐solvent interaction, like “good” or θ solvent, are not suitable for predicting the tendency of s‐PMMA to aggregation. The formation of aggregates evidently has some connection with the effect of the solvent upon the conformational structure of syndiotactic sequences.
Diffusion‐controlled growth of lamellar crystals in an isotactic polystyrene–polyphenylene oxide blend
Authors: Hachmann U. , Petermann J.
Published: April 2003

The growth rates of lamellar crystals grown onto preseeded fibrillar crystals (“shishes”) in isotactic polystyrene and blends of isotactic polystyrene (iPS) with polyphenylene oxide are followed by using transmission electron microscopy. The preseeded fibrillar crystals avoid the problem of timedependent primary nucleation. The time dependence of lamellar growth is investigated. At a concentration of 50% PPO in iPS, the lateral lamellar growth rate of the precipitating isotactic polystyrene crystals conforms to a time law characteristic of diffusion‐controlled growth (R ∝ t1/2). Diffusion coefficients are estimated from the growth kinetics. The method could prove a simple means of measuring diffusion coefficients in polymer blends in which one component is crystallizable.
The effect of interlamellar forces on the longitudinal acoustic mode of polyethylene crystals
Authors: Runt J. , Hanrahan B. D. , Harrison I. R.
Published: April 2003

The fold periods and longitudinal acoustic modes [LAMs] for isothermally crystallized polyethylene (PE) single crystals were determined in the dried state and in the presence of decalin and silicone oil. Upon swelling with decalin, the fold period increased by 7% while the LAM peak frequency decreased by approximately 1 cm−1. Several possible explanations for the change in LAM frequency are discussed but the exact interpretation is open to question. No change in fold period was observed upon soaking a dried crystal mat in silicone oil. This fold period invariance along with the fact that silicone oil has no effect on the melting point of PE crystals indicates that there is no significant interaction between the oil and the methylene groups on the crystal surface. The effect of suspending crystals (which have never been dried down) in silicone oil should only be to increase the average interlamellar distance and, therefore, to reduce any interlamellar forces. It is shown that the LAM peak frequency for crystals suspended in silicone oil is the same as that for the dried crystals, indicating that interlamellar forces do not exert a significant perturbing influence on the LAM of polyethylene crystals.
A new look at the crystallization of polyethylene. II. Crystallization from the melt at low supercoolings
Authors: Chivers R. A. , Barham P. J. , Martinez‐Salazar J. , Keller A.
Published: April 2003

This article is part of the general project laid out in Part I (ref. 9) and is concerned with obtaining information on primary (unthickened) crystals of polyethylene formed at low supercoolings. For this, a technique had to be devised by which crystallization could be speeded up so as to eliminate or at least reduce lamellar thickening. Indeed we were able to increase the rate of crystallization by an order of magnitude using a technique which we have called enhanced self‐nucleation. Using this technique we find that when viewed under an optical microscope, spherulites crystallize uniformly over the field of view, and not, as is usual, by a radial growth process. Isothermal crystallization in bulk linear polyethylene has been studied by means of the enhanced self‐nucleation technique as a function of crystallization time by using Raman LAM and melting points to assess variations of fold length Data have been obtained at very much shorter times than before. At short times, we find a constant fold length; at longer times the crystals thicken linearly with the logarithm of time. Values of the initial fold length for crystallization temperatures between 118 and 130°C are presented. Associated with the thickening at short times we find an induction time which increases with temperature.
Highly conductive meta derivatives of poly(phenylene sulfide)
Authors: Elsenbaumer R. L. , Shacklette L. W.
Published: April 2003

Changes in the backbone structure of several meta derivatives of polyphenylene sulfide upon doping with AsF5 have been investigated by IR spectroscopy. Poly(m‐phenylene sulfide) does not form a conducting complex with AsF5 unless reacted under conditions where carbon‐carbon bonds form intramolecularly between phenyl rings. This assertion has been verified by comparison of the IR spectra of poly(m‐phenylene sulfide) and a newly synthesized derivative, poly(thio‐3,7‐dibenzothiophendiyl), after doping with AsF5. This new derivative forms a complex with AsF5 which exhibits a conductivity of 18.5 S/cm. A sulfone‐containing derivative has also been synthesized, poly[thio‐3,7‐(dibenzothiophene‐5,5‐dioxide)‐diyl]. With this polymer, a much lower conductivity, 10−3 S/cm, was obtained after exposure to AsF5.
Bisphenol‐A polycarbonate–poly(butylene terephthalate) transesterification. I. Theoretical study of the structure and of the degree of randomness in four‐component copolycondensates
Authors: Devaux J. , Godard P. , Mercier J. P.
Published: April 2003

This article is the first of a series devoted to various aspects of exchange reactions in molten bisphenol‐A polycarbonate–poly(butylene terephthalate) mixtures. The statistical aspects of exchange reactions between two polycondensates of different chemical structure are considered. This theoretical approach enables us to calculate the mean lengths of the various sequences as well as several expressions for the degree of randomness in four‐component copolycondensates from triad or dyad concentrations as determined by NMR spectroscopy.
Crack velocity dependence of electron emission during fracture of filled elastomers
Authors: Dickinson J. T. , Jensen L. C.
Published: April 2003

In this article we examine the electron emission accompanying the fracture of filled elastomers, where in previous work we have shown the emission to be intense and due predominately to interfacial failure. In this study we show that there is a strong velocity dependence on the rate of electron emission during the propagation of a crack in filled silicone rubber and polybutadiene filled with glass beads. This dependence cannot be explained by a simple proportionality between emission rate and rate of surface area production. We propose that the concentration of free radicals produced by crack propagation increases rapidly with crack velocity which in turn produces more intense electron emission by a chemiemission mechanism.
The dependence of the glass transition temperature of poly(N‐vinylcarbazole) upon steric microstructure and molecular weight
Authors: Terrell D. R. , Evers F. , Smoorenburg H. , van den Bogaert H. M.
Published: April 2003

Poly(N‐vinylcarbazole) (PVK) samples were found to exhibit up to three glass transition temperatures Tg, corresponding to the whole chain and the syndiotactic and isotactic stereoblocks. An increasing tendency to multiple Tgs, and hence to phase separation, was observed with increasing isotacticity. Limiting values at infinite molecular weight for syndiotactic and isotactic PVK were obtained from correlations of the Tgs corresponding to the syndiotactic and isotactic stereoblocks with their respective average stereoblock lengths derived from 13C NMR measurements. They were found to be 549 and 399 K, respectively. The conventional Tg for PVK was found to exhibit the following dependence upon the syndiotactic dyad mole fraction Xs:

The molecular weight dependences of the conventional Tgs for several fractionated PVK samples obeyed a Fox–Flory‐type relation with values of −dTg/d(1/M) varying between 7.6 × 103 for isotactic PVK and 2.7 × 105 for Luvican M 170.
Multiphase equilibria in solutions of polydisperse homopolymers. I. Three‐phase equilibria in ternary and quasiternary systems
Authors: Šolc Karel
Published: April 2003

A recent critique of the mechanism of three‐phase separation suggested by Tompa for ternary system solvent–polymer (1)–polymer (2) is shown to be invalid, and Tompa's account is reinforced by analytical arguments and numerical results. In particular it is proven that the critical point in some simple Flory–Huggins systems is thermodynamically unstable, rather than just metastable. Three‐phase separations in quasiternary systems cannot be studied by simple methods advanced for treatment of true ternary systems. Rather a new, more general, approach is required for these cases.
The nonlinear viscoelastic behavior of a carbon‐black‐filled elastomer
Authors: Sullivan J. L. , Demery V. C.
Published: April 2003

The stress relaxation behavior of a carbon‐black‐filled elastomer is shown to be independent of the state of deformation, and the temperature dependence of its static modulus is in good accord with that predicted by the statistical theory of elasticity. The storage and loss moduli are found to be separable functions of frequency and overall strain effects in both simple tension and pure shear. A separability of static deformational and dynamic strain amplitude effects is found for the storage modulus, but could not be determined for the loss modulus. However, the loss tangent is found to be a function of the static state of deformation. From these experimental results, it is shown that an existing viscoelasticity theory for an unfilled system when specialized to uniaxial extensions has a form which can be made suitable for representing the dynamic behavior of filled systems by the introduction of two functions of the dynamic strain amplitude.
Spectroscopic characterization of the matrix–silane coupling agent interface in fiber‐reinforced composites
Authors: Chiang Chwan‐Hwa , Koenig Jack L.
Published: April 2003

The copolymerizations of anhydride‐cured epoxy resin on fiberglass surfaces treated with a N‐methylaminopropyltrimethoxysilane coupling agent has been investigated using Fourier‐transform infrared spectroscopy. The structure of the interface of the silane and the resin in fiber‐reinforced composites is composed of copolymers of the epoxy resin with the organofunctionality of the deposited silanes. The number of interfacial bonds formed depends on the amount of silane coupling agent deposited on the fiberglass and the reaction conditions. The silane induces additional esterification and increases the curing density of the epoxy matrix near the fiber surface by about 5–10% relative to the bulk resin.
Study of molecular motion in polysilastyrene by pulsed 1H nuclear magnetic resonance
Authors: McGarvey Bruce R. , Schlick Shulamith
Published: April 2003

Pulsed NMR spectra of protons in polysilastyrene, $ \rlap{--} [{\rm Si(CH}_{\rm 3} {\rm )}_{\rm 2} {\rm  Si(CH}_{\rm 3} )({\rm C}_6 {\rm H}_5 )\rlap{--} ]_n $, with n ≈ 60, have been measured in the temperature range 80–450 K. The linewidth is constant at 7.4 G up to 200 K and narrows considerably above 250 K to a constant value of 0.3 G above 360 K. The motion responsible for this effect has an activation energy of 43.7 kJ/mol and is identified with the large‐scale motion occurring in the vicinity of the glass transition temperature. The spin‐lattice relaxation time T1 was measured by the π‐t‐½π pulse sequence as a function of temperature. Two motional minima in T1 were observed. The low‐temperature motion has an activation energy of 3.7 kJ/mol and is identified with methyl group reorientation. The high‐temperature motion has an activation energy of 29.1 kJ/mol and might be due to segmental motion.