bluuebunny/crossref_metadata_2025_split huggingface dataset:
A laser light‐scattering study of the structure of agarose gels
Authors: Key P. Y. , Sellen D. B. 
Published: April 2003

AbstractDiffusion coefficients of dextran fractions within agarose gels surrounded by dextran solution have been measured by laser light scattering using the autocorrelation method. Plots were made of the diffusion coefficient relative to that in dilute solution, D/D0, against the logarithm of hydrodynamic diameter logd for each concentration of agarose, and superimposed by displacing horizontally to produce a unified plot. In this way it was shown that D/D0 is a function of Cbd, where C is agarose concentration, with b = 1/3 and 1/2 for the cases in which the dextrans were mixed in before gelation and allowed to diffuse in afterwards, respectively, the plots being the same for a reference concentration of 0.7%. A value of b = 1/2 is that which would be expected if the molecular weight per unit length of the gel fibers were independent of concentration, and a value of 25 kg mol−1 nm−1 is calculated. Mobile concentrations of dextran within the gels relative to those in the surrounding solutions were found by determining the scattered intensity associated with the diffusing dextran molecules from the zero‐time value of the autocorrelation function. All results and calculations are discussed in terms of current theories, and compared with earlier work on calcium alginate gels for which a molecular weight per unit length of gel fiber of 0.59 kg mol−1 nm−1 was calculated. The nature of the spectral broadening of the light scattered from agarose gels in the absence of dextran is described.
Mechanical relaxation mechanism of epoxide resins cured with aliphatic diamines
Authors: Ochi Mitsukazu , Okazaki Masatoshi , Shimbo Masaki 
Published: April 2003

AbstractThe mechanism of low‐temperature relaxations in bisphenol‐A‐type epoxide resins cured with aliphatic diamines, with aliphatic diamines in the presence of salicylic acid as an accelerator, and with tertiary amines was investigated to compare the dynamic mechanical properties and the chemical structure of these networks. Mechanical relaxations are observed at about −140 and −60°C. The former relaxation is denoted the γ relaxation and the latter the β relaxation. The β relaxation of the cured epoxide resins containing hydroxyether groups is a sum of contributions from the relaxation of these groups and of other parts of the network structure. A new relaxation due only to the motion of the hydroxyether group can be estimated from the difference of tanδ curves between the aminecrosslinked and ether‐crosslinked systems. The γ relaxation is attributed to the motion of a polymethylene sequence consisting of at least four carbon atoms.
The temperature dependence of the viscoelastic softening and terminal dispersions of linear amorphous polymers
Authors: Plazek Donald J. 
Published: April 2003

AbstractThermorheological simplicity is shown to hold for poly(vinyl acetate) in the temperature range extending from Tg + 25°C to Tg + 80°C. Between Tg and Tg + 25°C the softening (glass to rubberlike) viscoelastic dispersion exhibits time‐scale shift factors aT different from those of the terminal (rubberlike to steady‐state) dispersion. The aT values calculated from zero‐shear viscosities coincide with those from the terminal dispersion in the temperature range 60–154°C (Tg ≅ 35°C). The aT shifts obtained from the response in the terminal dispersion can be fitted to the Williams, Landel, and Ferry equation over the entire temperature range 42–154°C. The aT obtained from the softening dispersion is shown to exhibit a different functionality. An empirical modification of the Doolittle equation yields a very flexible relation which can be fitted to some aTs which cannot be represented by the usual Doolittle free‐volume expression.
An expression for local composition in polymer‐solution thermodynamics
Authors: Canovas A. A. , Rubio R. G. , Renuncio J. A. R. 
Published: April 2003

AbstractAn expression for local composition which describes nonrandom interactions between unlike molecules in polymer solutions is proposed. This expression makes the nonrandom model compatible with the one‐fluid hypothesis and satisfies the limits of randomness when experimental conditions evolve in such a way. Data on several binary systems are studied using this model which represents simultaneously activity and heat‐of‐mixing data.
Moderately concentrated solutions of polystyrene. I. Viscosity as a function of concentration, temperature, and molecular weight
Authors: Hager B. L. , Berry G. C. 
Published: April 2003

AbstractData on the viscosity η of moderately concentrated solutions of polystyrene are reported. Several solvents were investigated, including cyclopentane solutions over a temperature span between θU = 19.5°C and θL = 154.5°C. The data were analyzed in terms of a relation giving η as a function of αφM, where αφ is the expansion factor for the chain dimensions in a solution with volume fraction φ of polymer with molecular weight M. It is shown that values of αφ so determined decrease as ∂ lnαφ/∂ lnφ = (1 − 2μ)/6μ for φ greater than φ* = 0.2M/s3 for moderately concentrated solutions, where s is the root‐mean‐square radius of gyration and μ = ∂ ln[η]/∂ lnM with [η] the intrinsic viscosity.
Simulation of reversible polycondensations with monomer having reactivity different from that of higher homologs
Authors: Gupta Santosh K. , Agarwalla N. L. , Rajora P. , Kumar Anil 
Published: April 2003

AbstractReversible AB‐type polycondensations have been simulated in a batch reactor where the monomer reacts with itself or any higher oligomer with a rate constant R times that for higher mers. Similarly, the rate of reaction of the condensation product with an AB group at the end of a polymer chain has been assumed to be R' times that with an “internal” AB group. The variation of the number‐average chain length μn with time (until equilibrium is reached) has been obtained. μn is found to be lower and the polydispersity index higher in the presence of the reverse reactions. Where the equilibrium conversions are high enough, a split in the molecular‐weight distribution (MWD) curves is observed for even‐ and odd‐order homologs for R < 1, though this effect is considerably diminished as compared with that in similar irreversible polycondensations. It is also found that the most probable distribution does not adequately represent the MWD when the functional groups violate the equal‐reactivity hypothesis and number‐average chain lengths are relatively small.
Defects in polydiacetylene single crystals. II. Dislocations in pTS
Authors: Young R. J. , Petermann J. 
Published: April 2003

AbstractThe structure of single crystals of a substituted diacetylene polymer (pTS) has been investigated by using transmission electron microscopy. It has been found that edge dislocations with Burgers vector parallel to the chain direction are present at a density of up to 1013 m−2. It is suggested that the dislocations may be present first of all in the monomer crystals and become locked into the monomer structure during polymerization. It has been found that the dislocations have a tendency to line up in rows perpendicular to the chain direction and when the density of the dislocations in a row is sufficiently high a small−angle grain boundary can be formed. A possible structure for the dislocations on a molecular level is suggested and the effect of the presence of the dislocations upon the polymerization behavior, mechanical properties, and electric properties is discussed.
Magnetic effects and viscosity in the nematic phase of a polymer series
Authors: Hardouin F. , Achard M. F. , Gasparoux H. , Liebert L. , Strzelecki L. 
Published: April 2003

AbstractMagnetic measurements were made on a series of polyesters in their nematic state and compared to their apparent viscosity at the same temperature. At similar molecular weights, the length of a flexible segment in the main‐chain polymer plays an important role in both the magnetic orientation effects and the apparent viscosity behavior. Moreover, on cooling from a perfectly oriented nematic sample, the alignment remains down to room temperature. In contrast with nematic monomers, these polymers behave like solids, even at the lowest velocity of a rotating magnetic field.
Birefringence of highly oriented fibers
Authors: Yang H. H. , Chouinard M. P. , Lingg W. J. 
Published: April 2003

AbstractA spectrophotometric method was developed for measuring the birefringence of highly oriented synthetic fibers. This method surmounts the low birefringence limit of the standard quartz compensator method and the difficulties in interpretation of the photographic fringe method. A highly oriented aramid fiber gave birefringence values of 0.60–0.75 by this method, compared with 0.25 for polyester and 0.06 for nylon by other conventional methods. The operating principles and excellent results of this new method provide a basis for the extension of routine birefringence characterization to highly oriented fibers.
One‐dimensional order/disorder in a polydiacetylene
Authors: Patel G. N. , Khanna Y. P. 
Published: April 2003

AbstractA polydiacetylene film, found to be amorphous by x‐ray diffraction, possesses some kind of order as suggested by differential scanning calorimetry (DSC). The order/disorder phenomenon which occurs upon heatingcooling is also accompanied by a green/yellow color transition. On the basis of analogies between crystallization and the order in this material, we have extended the application of the Avrami equation to determine the dimensionality of the order in the polymer. Kinetic analysis of the exothermic transition (disorder → order) by DSC suggests that the material has one‐dimensional order. The disruption and formation of this order, which accompany the color changes in this polydiacetylene, give rise to endothermic and exothermic transitions, respectively. Supporting evidence for the proposed one‐dimensional order/disorder concept is cited.
NMR studies of molecular mobility in uniaxially stretched oriented polymers
Authors: Egorov E. A. , Zhizhenkov V. V. 
Published: April 2003

AbstractThe effect of elasticlike uniaxial tension on molecular mobility in polymers have been studied over a wide temperature range using the broad‐line NMR technique. The studies were carried out on oriented semicrystalline samples of nylon 6, poly(ethylene terephthlate), polypropylene, polyethylene, polyoxymethylene, poly(vinyl alcohol), and polytetrafluorethylene. Above the low‐temperature transition the NMR spectra are reversibly transformed under tension. Increases in the second moments of the spectra are attributed to weaker molecular motion in stressed polymers. The only exception is polypropylene, in which the reverse, i.e., enhancement of molecular mobility, can be observed in a certain temperature range. In the spectra of polymers stretched above the glass transition temperature the narrow component decreases, thus indicating inhibition of micro‐Brownian motion, a phenomenon we call “mechanical vitrification.” Such mechanical vitrification is proved to result from reduction in the number of possible tie‐chain conformations in the non‐crystalline regions and not from closer packing of chains. In discussing the results we use the experimental data on the reduction of the number of gauche isomers under tension (on average, one transition of a gauche link to the trans state causes at least five methylene groups in the main chain to become immobile). The results of studies of molecular mobility in stretched polymers are used for more accurate definition of the mechanisms of molecular motion at different temperatures. A method for evaluation of the energy of intermolecular interactions which hinder small‐scale motion at low temperature is suggested.
Shrinkage and retractive forces during the annealing of drawn low‐density polyethylene
Authors: Decandia F. , Russo R. , Vittoria V. , Peterlin A. 
Published: April 2003

AbstractShrinkage of unconstrained low‐density polyethylene samples and the retractive stress of samples with ends fixed have been investigated as a function of the annealing time tA and temperature TA on material drawn at room temperature to draw ratios λ between 4 and 6. The shrinkage increases with tA and TA. The retractive stress on a sample annealed with ends fixed goes through a maximum as the sample is annealed and then drops to a limiting value which increases with TA as long as TA is at or below 80°C and rapidly decreases with higher TA. The drop from the maximum to the limiting retractive stress, slow at lower TA and rapid at higher TA, seems to be a consequence of rapid pulling of chain segments out of crystal block in which interfibrillar tie molecules are anchored. This process is facilitated by the high TA, which softens the crystal matrix. At constant end‐to‐end distance, the contour length of the tie molecules is irreversibly increased, and this causes a reduction in the contribution of the affected tie molecules to the overall retraction stress. Hence one finds a substantially higher retraction stress during first heating than during subsequent cooling and heating of the drawn sample.
Etude cinétique des effets de fluence énergétique, de débit de fluence, et d'effacement induits par des ions lourds et des photons γ dans le triacétate de cellulose
Authors: Moliton J. P. , Boutinaud C. , Vareille J. C. , Decossas J. L. , Teyssier J. L. , Delaunay B. 
Published: April 2003

AbstractThe kinetic interpretation of the damage produced by heavy ions (Kr and Cl from 1 MeV/amu) and γ radiation in cellulose triacetate leads to an exponential dependence on the ion fluence. A comparison of the fading effect produced by heavy ions and γ rays shows that the heavy ions, unlike γ rays, cause irreversible damage. Finally, a nonlinear dependence on the flux of ions and γ rays is found in the kinetics of radiation damage. This result is contrary to the usual assumption that heavy‐ion flux, like γ‐ray flux, is additive, at least for the fluxes of 109−2 × 1010 ions/cm2s and dose rates of 103–104 Gy/h used in this work.
Liquid‐crystalline textures in binary and ternary block copolymer–solvent systems
Authors: Wittmann J. C. , Lotz B. , Candau F. , Kovacs A. J. 
Published: April 2003

AbstractA number of characteristic liquid‐crystalline textures can be obtained in binary and ternary systems (i.e., including one or two solvents) based on polystyrene‐poly(ethylene oxide) (PS‐PEO) and polystyrene‐polyisoprene block copolymers. These textures include oily streaks, myelinic figures, and vesicles, all characteristic of a lamellar structure; fan‐shaped textures of cylindrical structure; and isotropic domains indicative of a cubic structure. Experimental conditions used to systematically produce the mesomorphic textures are described, and the rather critical solubility conditions which the solvents must meet are indicated. The rules and described procedures should be quite general and applicable to other copolymers as well. Finally, highly unusual examples of “pseudomorphosis” typical of liquid‐crystalline textures occurring in bulk upon melting and crystallization of the PEO sequences in PEO‐PS copolymers are also reported.
Infinite‐dilution oscillatory flow birefringence properties of polystyrene and poly(α‐methylstyrene) solutions
Authors: Lodge Timothy P. , Miller James W. , Schrag John L. 
Published: April 2003

AbstractOscillatory flow birefringence (OFB) measurements have been carried out for an extensive series of solutions containing narrow‐distribution, atactic, linear polystyrenes PS (10, 000 or 390, 000 Mw) or poly(α‐methylstyrene) PMS (400,000 Mw) in a high‐viscosity solvent, Aroclor 1248. The concentration ranges examined are such that the concentration dependence is obtained in both the “dilute” and “semidilute” regimes; the data are sufficiently precise to permit extrapolation to obtain for the first time the infinite‐dilution properties. Various plotting formats are explored to determine an appropriate extrapolation procedure. The infinite‐dilution OFB properties are compared with the bead‐spring model (Zimm) theory which predicts quantitatively the frequency dependence of the observed properties for the PS and PMS solutions studied except for the high‐frequency regime. The sensitivity and precision of the OFB experiment is such that the extrapolation curves–and the resulting infinite‐dilution properties–show substantially less scatter than comparable visco‐elasticity (VE) data. There is no evidence of a change in the character of the concentration dependence for the range of concentrations studied.
Effects of data analysis on accuracy and precision of GPC results
Authors: Tchir W. J. , Rudin A. , Fyfe C. A. 
Published: April 2003

AbstractThe effects of data imprecision and baseline uncertainties have been investigated by computer simulation of GPC data from a polymer sample with a truncated log‐normal molecular weight distribution. If the data are very accurate, as few as five data points can be sampled without serious error in computed molecular weight averages. The number of data points required is much larger, however, if these are taken at equal increments of molecular weight rather than elution volume. The effects of noise can be counteracted by increasing the sampling frequency. Baseline uncertainties present a more serious problem, especially for broad‐distribution samples. If the detected signal is too noisy to permit accurate location of the baseline, errors can be minimized by using a second, more sensitive detector to determine the peak start and end. It is very difficult to estimate M̄z and higher molecular weight averages accurately if the noise level is greater than 0.5%.
Light‐scattering studies on polystyrenes in isorefractive poly(methyl methacrylate)–toluene “solvents”
Authors: Lin C.‐Y. , Rosen S. L. 
Published: April 2003

AbstractThe rms radii of gyration 〈S2〉1/2 and second virial coefficients Γ2 of five monodisperse polystyrenes (M × 10−5 = 1.6, 2.8, 4.2, 6.6) were measured in isorefractive toluene–poly(methyl methacrylate) (M̄v = 4.0 × 104, 1.6 × 105, and 6.3 × 105) “solvents.” For a given PMMA, the concentration at which the θ condition (defined by Γ2 = 0) was reached was independent of PS molecular weight, but varied inversely with PMMA molecular weight (0.10, 0.056, and 0.023 g/mL, respectively). When this θ condition is reached by adding PMMA to toluene, the radii of gyration are decreased by only about 15%, much less than when it is reached by going to a poor, low‐molecular‐weight solvent. This reflects the exclusion of PMMA from the PS coils, the internal environment of which is essentially pure toluene.
Microphase separation in sulfonated polystyrene ionomers
Authors: Peiffer D. G. , Weiss R. A. , Lundberg R. D. 
Published: April 2003

AbstractSmall‐ and wide‐angle x‐ray scattering results for a series of un‐neutralized and neutralized sulfonated polystyrenes are presented for the range of sulfonation from 0 to 7.26 mol %. From the small‐angle scattering it is shown that above the 3 mol % level for both the zinc and sodium salts, a Bragg spacing (37 Å) and diameter (6.9–8.4 Å) of the scattering unit can be calculated. When the concentration of salt is increased, there is no appreciable change in the latter two measurements. The wide‐angle data indicate that the cations do not influence to any large extent the basic intramolecular and intermolecular structure of polystyrene. All the data are consistent with the onset of clustering above a critical ion concentration.
Properties of aqueous salt solutions of poly(ethylene oxide)
Authors: Ataman M. , Boucher E. A. 
Published: April 2003

AbstractThe determination of the properties of aqueous salt solutions of poly(ethylene oxide) has been extended to cloud‐point and θ‐temperature measurements in sodium acetate, potassium fluoride, sodium thiosulfate, and potassium phosphate. The Hofmeister series for the decreasing effect of anion species in salting out the polymer is accordingly extended. However, the order of the effect depends on whether it is made on the basis of molar anion concentration the molar concentration of unit anion charge, or the ionic strength. Viscosity measurements on θ and non‐θ solutions containing zinc sulfate, potassium fluoride, and potassium phosphate gave polymer dimensions (in addition to limiting viscosity numbers etc.), and characteristic ratios in good agreement with theoretical predictions (Abe and Mark), and enthalpy and entropy parameters χH and χs; the latter values, nominally −0.14 and 0.63, are identical at 298 K for the three salt species.
Polymerization and reptation, an analytical treatment
Authors: Boots H. M. J. 
Published: April 2003

AbstractFree‐radical polymerization without crosslinking is considered. By taking the chain length as a continuous variable the reaction kinetics is treated in a simple way for the stationary state. Equations for instantaneous average degrees of polymerization and related quantities are generalized to allow for chain‐length dependence of the termination rate constant. For the Ito model, which treats reptation‐controlled termination, approximate versions of these equations are derived in the limits of low and high conversion. The observed structure in the peak of the gel permeation chromatograms is shown not to be related to the bimodality in the instantaneous molecular weight distribution. None of the results is very sensitive to the precise reptation behavior.
A new look at the crystallization of polyethylene. III. Crystallization from the melt at high supercoolings
Authors: Barham P. J. , Jarvis D. A. , Keller A. 
Published: April 2003

AbstractPolyethylene melts normally cannot be crystallized in an isothermally controlled manner below ca. 110°C as crystallization is too fast owing to the presence of preexisting nuclei. We here present a new simple method for producing droplets enabling crystallization to be conducted isothermally down to 75°C and allowing measurements to be performed on them, together with the results of these measurements. We conclude that in contrast to the earlier claims the homogeneous nucleation regime has not been attained even at these low temperatures, the crystal nucleation being dominated by the polymer‐substrate interface. The droplets crystallized at these low temperatures have a lamellar morphology as revealed by electron microscopy and grow at rates exceeding 1 m s−1[i.e., six orders of magnitude faster than growth at more usual crystallization temperatures previously considered as “low” (110–120°C)]. We have measured the lamellar thicknesslas a function of growth temperature, thus extending the fundamentally importantlvs. ΔT(supercooling) relation beyond the previously realizable limits towards high ΔTvalues. The implications of all these results for the existing ideas of polymer crystallization are likely to be far reaching. Further, the new method for achieving high supercoolings opens up new possibilities for the study of annealing phenomena and the effect of nucleating agents.