bluuebunny/crossref_metadata_2025_split huggingface dataset:
Application of scaling concepts to sedimentation phenomena in semidilute macromolecular solutions
Authors: Roots Jaan , Nyström Bo 
Published: April 2003

AbstractSedimentation velocity data on polystyrene in a good solvent (toluene) and in a theta solvent (cyclopentane), over a large concentration range are reported. Under good‐solvent conditions the exponent β in the apparent scaling law describing the concentration dependence of the sedimentation coefficient (s ∝ cβ) in the semidiiute region is found to be concentration dependent. However, a power law fit to data for the highest molecular weight (M = 20.6 × 106) in the concentration region (c < 2 kg m−3) yields a value β = −0.59, somewhat smaller than that (−0.54) predicted theoretically. This discrepancy and the observed curvature in logs vs. logc at higher concentrations are discussed. Under theta‐solvent conditions, on the other hand, the concentration dependence of s in the semidilute regime can be represented by a simple power law, with β = −1.0, in excellent agreement with the theoretical prediction. The crossover concentration c*, separating the dilute and semidilute concentration regimes, was found to be well defined and located at c = 1/[η]. c* varies with molecular weight as M−0.73 and M−0.50 under good‐solvent and theta‐solvent conditions, respectively.
SAXS instrumental broadening and the order dependence of peak width
Authors: Harrison I. R. , Kozmiski S. J. , Varnell W. D. , Wang J.‐I. 
Published: April 2003

AbstractThe width at half‐height of SAXS discrete diffraction peaks has been used to compute the number of polyethylene lamellae in a stack. The dependence of this width on diffraction order reflects the nature and magnitude of lattice fluctuations. Within the literature there have been conflicting reports on this order dependence and hence on the nature of the lattice fluctuations. Previous studies have neglected the effects of instrumental broadening. These present studies show that instrumental effects can account for some 40% of the observed first‐order peak width and drastically change the ratio of peak widths as a function of order. These studies, carried out on isothermally grown polyethylene single‐crystal mats, also demonstrate the importance of the functions chosen to represent the various broadening factors. A mat was made up consisting of randomly stacked lamella with two distinct fold periods. The scattering from this mixed mat could not be described by either of the prevailing theories.
Model polyurethane elastomers prepared from noncrystallizable poly(propylene oxide) chains
Authors: Sung P.‐H. , Mark J. E. 
Published: April 2003

AbstractElastomers of controlled molecular structure were prepared from hydroxyl‐terminated atactic poly(propylene oxide) (PPO) chains having number‐average molecular weights Mn in the range 800–4360 g mole−1. The chains were end‐linked into noncrystallizable trifunctional networks using a specially prepared aromatic triisocyanate. The networks thus obtained were studied with regard to their stress–strain isotherms in the unswollen state, in elongation at 25°C, and with regard to their equilibrium swelling in benzene at 61°C. Values of the modulus in the limit at high deformation were in good agreement with corresponding results previously obtained on networks of poly(dimethylsiloxane) (PDMS). This is of considerable importance since use of the widely used “plateau modulus” as a measure of interchain entangling would suggest that the networks of PPO would have a much higher density of such entanglements than would the corresponding networks of PDMS. The close similarity between the moduli of the two types of networks therefore argues against the idea that such entanglements make large contributions to the equilibrium elastomeric properties of a polymer network. These values of the high deformation modulus are also in good agreement with recent molecular theories as applied to the nonaffine deformation of a “phantom” network. The values of the low deformation modulus were considerably smaller than the values predicted for an affine deformation, however, suggesting that the junction points were not firmly embedded in the network structure. This is presumably due to the relatively low degree of chain‐junction entangling in the case of relatively short network chains. The swelling equilibrium results were in very good agreement with the new theory of network swelling developed by Flory.
Infrared spectroscopic study of solvent‐induced structural changes in poly(ethylene terephthalate) film
Authors: Khan A. H. , Venkatesh G. M. 
Published: April 2003

AbstractIt is found from polarized infrared spectroscopy that treatment of oriented poly(ethylene terephthalate) (PET) film with strongly interacting solvents such as s‐tetrachloroethane, nitrobenzene, dimethylformamide, and benzyl alcohol results in disorientation of polymer chains. Partial transformation from trans to gauche conformation takes place on thermal treatment and, to a larger extent, on solvent treatment. Increasing sharpness of the 988 cm−1 band on solvent treatment indicates the formation of regular chain folds. Some new spectral features are discussed.
Model networks of end‐linked polydimethylsiloxane chains. XI. Use of very short network chains to improve ultimate properties
Authors: Llorente M. A. , Andrady A. L. , Mark J. E. 
Published: April 2003

AbstractElastomeric networks were prepared by tetrafunctionally end‐linking mixtures of various proportions of relatively long and very short polydimethylsiloxane (PDMS) chains. The former had a number‐average molecular weight of 18,500 and the latter either 660 or 220 g mole−1. The series of (unfilled) bimodal networks thus prepared were studied in elongation to the rupture point at 25°C, and in swelling equilibrium in benzene at room temperature. Elasticity constants characterizing the Gaussian regions of the stress–strain isotherms, and values of the degree of equilibrium swelling were used to evaluate the most recent molecular theories of rubberlike elasticity. The isotherms also gave values of the elongation at which the modulus begins to increase anomalously because of limited chain extensibility, and values of the elongation and nominal stress at the point of rupture. These results were interpreted in terms of the known configurational characteristics of the constituent PDMS chains. Values of the energy or work required for rupture were used as an overall measure of the “toughness” of the networks. The very short chains were found to give a marked increase in toughness, through an increase in ultimate strength without the usual corresponding decrease in maximum extensibility. A variety of additional experiments will be required in order to elucidate the molecular origins of this important effect.
Structural differences between two crystal modifications of poly(γ‐benzyl L‐glutamate)
Authors: Watanabe Junji , Imai Kazumichi , Gehani Ramesh , Uematsu Ichitaro 
Published: April 2003

AbstractX‐ray diffraction patterns were obtained for as‐cast and oriented films of poly(γ‐benzyl L‐glutamate) and a comparison was made of the molecular packing of the α‐helices in forms B and C. Form B snowed Bragg reflections on the layer lines as well as on the equator. The spacings were explained by a monoclinic unit cell comprising two chains, with a = 29.06 Å, b = 13 20 Å, c = 27.27 Å α = γ = 90°. and β = 96°. The chains contained in this unit cell and consequently alternating in the crystal have opposite chain directions. Form C showed continuous scattering on the layer lines and reflections on the equator. This form, therefore, is a nematiclike paracrystal in which the packing of α‐helices is periodic in the direction lateral to the chain axis (a = 14.8–115.2 Å, b = 14.3–14.8 Å, c = 27 Å, and γ = 118°–120°), but the relative levels of the chains along the chain axes are displaced. The formation of form C may be attributed to random placement of two chains with mutually opposite chain directions.
Morphology and structure of heavily deformed single crystals of a polydiacetylene. II. Resonance raman and optical spectroscopy
Authors: Batchelder D. N. , Kennedy R. J. , Bloor D. , Young R. J. 
Published: April 2003

AbstractResonance Raman and optical spectroscopy have been used to study foils having a metallic appearance which were produced by the hammering or rolling of single crystals of toluene sulfonate diacetylene polymer. The spectroscopic properties of the bulk material in the foils were found to be almost indistinguishable from those of underformed crystals. In contrast, the blue–green surface skin of the foils appeared to consist of intact polymer chains without significant crystalline order.
Polyesters containing ring units in the main chain. II. Effects of size and mobility of rings on molecular relaxations
Authors: Matsumoto Naoji , Kumanotani Ju 
Published: April 2003

AbstractMolecular relaxations of polyesters containing C5–C15 rings in the main chain have been studied by DSC, dielectric dispersion, and NMR. Results are discussed in relation to the size and mobility of the rings. The Tg or α‐relaxation peak moves to higher temperature with an increase in the ring size from C5 to C12, but the effect is accompanied by an even–odd alternation with ring size. The β relaxations in dielectric dispersion reflect local‐mode motion of ester groups and are affected by steric interactions with the rings. Motions of the ring methylenes of C12 and C15 ring units are detected below Tg by broad‐line NMR.
Computer simulation of two‐dimensional spherulite growth
Authors: Gałȩski A. 
Published: April 2003

AbstractThe two‐dimensional growth of spherulites with impingement was simulated by a computer for athermal, thermal, and combined primary nucleation mechanisms. The simulation provided data on the spherulite size distributions and spherulite shapes. The results of the computer simulation were compared with experimental data on poly(methylene oxide) films.
Computer simulation of three‐dimensional spherulite growth
Authors: Gałȩski A. , Piórkowska E. 
Published: April 2003

AbstractA computer program for modeling three‐dimensional spherulite nucleation, growth, and impingement was elaborated. The Monte Carlo method was used to determine the degree of conversion and calculate the volume of the spherulites. Athermal, thermal, and mixed types of nucleation were tested. The experimental Avrami exponent agrees with the predictions for athermal and thermal nucleation while for mixed nucleation a nonintegral exponent is characteristic. The spherulite size distributions are very different from athermal and thermal nucleations. An intermediate pattern of distribution is proper for the mixed type of nucleation. The boundaries of the largest spherulites from thermal and mixed nucleation are concave while those of the smallest spherulites are convex.
Anisotropy of the dielectric constant of polyacetylene
Authors: Devreux F. , Döry I. , Mihály L. , Pekker S. , Jánossy A. , Kertész M. 
Published: April 2003

AbstractThe dielectric constant ϵ of polyacetylene films oriented by rolling was measured. The variation of ϵ and also that of the proton nuclear magnetic resonance line shape indicate that rolling partially isomerizes cis(CH)x. For oriented trans(CH)x we find ϵ∥ = 5.7 and ϵ⟂ = 4.0 in the plane of the film. A calculation based on bond polarizabilities leads to qualitative agreement with experiment.
Studies of environmental stress‐crack propagation in low‐density polyethylene
Authors: Bandyopadhyay S. , Brown H. R. 
Published: April 2003

AbstractCorrelations of the stress‐intensity factor K with crack speed a have been obtained for environmental stress cracking (ESC) of a series of low‐density polyethylenes in detergent. In the majority of the materials, the crack speed increases initially with increasing K, then becomes constant, and finally starts decreasing. The ESC resistance increases with increasing molecular weight and, in general, the quenched materials show greater ESC resistance than slowly cooled ones. The crack propagation results agree well with the ESC model of Williams. Attempts have also been made to understand the micromechanics of ESC failure from a combined approach of K, the crack tip characteristics, and the fracture surface appearance. The roughness of the fracture surface increases with increasing K.
Intrinsic viscosities of four homopolymers and one copolymer in nonpolar solvents. II. Effect of solvent steric hindrance
Authors: Filiatrault Danielle , Delmas Geneviève 
Published: April 2003

AbstractIntrinsic viscosities at 25°C of an ethylene‐propylene copolymer containing 81% ethylene (81% E) of polypentenamer (PPmer), polyisobutylene (PIB), polypentene‐1 (PP‐1), and polydimethylsiloxane (PDMS) have been measured in n‐C9 and three branched nonanes and n‐C7 and five branched heptanes. The effect of the solvent steric hindrance on the free energy, i.e., on the χ parameter was investigated. The highly sterically hindered, cruciform molecules 3,3‐dimethylpentane and 3,3‐diethylpentane are the best solvents for four of the five polymers. The enhancement of solvent quality due to the steric hindrance diminishes when the polymer free volume increases. The difference in [η] between 2,4‐dimethylpentane and 2,3‐dimethylpentane is −50%, −35%, −2% for PPmer, PIB, PDMS, and can be correlated to a measure of the polymer free volume, i.e., the lower critical solubility temperature. The χ, χH, and χS are calculated from [η] using the Stockmayer‐Fixman relation and from h, the heat of mixing at infinite dilution of the polymer, obtained previously. With each polymer, a good correlation is found between h and [η] obtained with the six heptanes and four nonanes. The correlation points to the same effect being at the origin of χH and χS but of different magnitude. In cases showing the steric hindrance effect, a negative contribution occurs in h (or χH) which is larger in magnitude than the corresponding negative entropic contribution leaving a net negative effect in χ itself. Probably due to their very compact shape and fewer degrees of freedom, the cruciform solvents lose less entropy than the chain solvents in mixing.
Brillouin scattering studies of poly(vinylidene fluoride) films subject to uniaxial stretching
Authors: Wang C. H. , Cavanaugh David B. , Hagashigaki Y. 
Published: April 2003

AbstractBrillouin scattering spectra of poly(vinylidene fluoride) films subject to stretching have been studied as a function of draw (stretch) ratios. The longitudinal sound velocity is found to be isotropic for the unoriented film, but as the film is stretched, the velocity along the direction of stretch becomes higher than that perpendicular to it. The increase in the sound velocity is due to the induced orientation of the chains in the amorphous and the crystalline regions. The Hermans orientation parameter has been determined as a function of stretch from the velocity data. The result indicates the occurrence of recrystallization and reorganization as a result of transformation to form I crystallites from the amorphous phase as the film is stretched.
Cage effects in recombination of allyl radicals in irradiated polyethylene
Authors: Hwang Lian‐Pin , Cheng Jung‐Tsang 
Published: April 2003

AbstractA cage model has been presented to describe the kinetics of recombination of radicals in solid polymer. The theory includes Torrey's treatment for jump diffusion and radiative boundary condition in the diffusion equation to account for the hindrance to the diffusion of macroradicals and the finite cage process of recombination reaction, respectively. The result has been applied to the interpretation of data on the decay of allyl radical in irradiated polyethylene.
Dielectric anisotropy in oriented poly(chlorotrifluoroethylene)
Authors: Choy C. L. , Cheng K. H. , Hsu Bay‐Sung 
Published: April 2003

AbstractDielectric measurements between −50 and 60°C have been made on isotropic and oriented samples of poly(chlorotrifluoroethylene) with draw ratios λ of 1 to 3.5 at frequencies ranging from 30 Hz to 1 MHz. For the oriented samples, the dielectric loss has been measured with the electric field normal (ε) and parallel (ε) to the draw direction. At low frequency (say 60 Hz) the loss data for the oriented samples reveal two peaks at 25 and −5°C, which are associated with the amorphous (γa) and the crystalline (γc) relaxations, respectively. Analysis of these data using a two‐phase model yields values for the amorphous orientation function fa which are only about 25 to 60% of those for the crystalline orientation function fc. Upon annealing, the anisotropy ε/ε at the γa peak decreases significantly while that at the γc peak remains largely unchanged. This implies a roughly unaltered fc and a large decrease in fa, which is consistent with the results of wide‐angle x‐ray diffraction and birefringence measurements.
Oriented polymers from solution. IV. Polyethylene/polypropylene blend films
Authors: Brown C. S. , Barham P. J. , Cannon C. G. 
Published: April 2003

AbstractWork on the surface‐growth method of producing blend films from mixed solutions of two polymers has exposed a random fluctuation in both growth rate and composition of the blend film with time of deposition. The effects are explained by heterogeneous separation of the two polymer components in the solution induced by the stirring action of the rotor of the Couette apparatus used. The solution is thus converted to a colloidal sol which on cooling forms a gel which exhibits syneresis at room temperature. The sol‐to‐gel transition is thermally reversible.
Dynamic mechanical properties of crosslinked polyurethanes containing sodium tetraphenylborate
Authors: Killis A. , LeNest J. F. , Gandini A. , Cheradame H. 
Published: April 2003

AbstractCrosslinked polyurethane elastomers consisting of low‐molecular‐weight polyethylene oxide or polypropylene oxide segments crosslinked with an aromatic triisocyanate have been studied. Networks have been prepared containing different amounts of sodium tetraphenylborate. The effects of temperature and salt concentration on their viscoelastic properties have been investigated by modulus and loss‐tangent measurements. Variations of the storage modulus with salt concentration or network chemical structure are directly correlated with variations in the glass transition temperature. In fact, superposition of the various modulus plots on a reduced temperature scale, T‐Tg, suggests that there is no dependence on salt concentration or polyether chemical structure.
Solid state characterization of the structure of chitosan films
Authors: Samuels Robert Joel 
Published: April 2003

AbstractFilms of chitosan, prepared by different fabrication processes, were examined at several structural levels, from the molecular to the macroscopic. This revealed the presence of polymorphic crystal forms, which varied with film treatment. Similarly, morphological structures varying from spherulites to rods were formed, depending on film processing conditions. The effect of structure on the mechanical properties, as well as the orientability of the films, were also investigated.
Structural study of conformational phases in poly(vinylidene fluoride) by far‐infrared spectroscopy
Authors: Latour M. , Montaner A. , Galtier M. , Geneves G. 
Published: April 2003

AbstractPolarized and unpolarized far‐infrared transmission spectra of poly(vinylidene fluoride) powders and films in the range 40–400 cm−1 are examined in terms of the α, β, and γ forms of this polymer. The bands which appear allow us to discuss various theoretical models. An interpretation of the polymer's configuration along and between chains including defects is proposed. Relations between the crystal form and treatments applied to the sample during its manufacture are demonstrated. In the same way the tttgtttg′ conformation previously reported by some authors for the γ form is corroborated.
Pressure‐induced freezing of conformational states of poly(vinyl chloride)
Authors: O'Reilly J. M. , Mosher R. A. 
Published: April 2003

AbstractThe pressure‐induced freezing of high‐energy conformations (trans‐gauche) of poly(vinyl chloride) has been measured by FTIR absorbance spectroscopy. The conformational change predicted from the increase in Tg with pressure and the change in population (absorbance) with temperature is larger than the observed change in population (absorbance). This difference is of the right order of magnitude as that predicted from the volume difference between conformers which favors the trans isomer at high pressure. Samples prepared at high pressure recover to their equilibrium population at the normal zero‐pressure glass temperature when heated with no applied pressure.
Studies of polar and nonpolar probes in the determination of infinite‐dilution solubility parameters
Authors: Lipson J. E. G. , Guillet J. E. 
Published: April 2003

AbstractPartial molar heats of mixing ΔH and Flory‐Huggins χ parameters have been determined for a series of polar and nonpolar organic probes in the polymer systems polychloroprene, poly(butadiene‐acrylonitrile) (34 wt. % acrylonitrile), poly(ethylene‐vinylacetate) (40 wt. % vinylacetate) and cis‐1,4‐polybutadiene in the range 65–85°C. Using the Flory‐Huggins χ parameters, infinite‐dilution solubility parameters δ were calculated for the polymers at 75°C to be 8.8 ± 0.2 for polychloroprene 10.0 ± 0.3 for poly(butadiene‐acrylonitrile), 8.3 ± 0.2 for poly(ethylene‐vinylacetate) and 7.9 ± 0.1 for polybutadiene. These δ values are in good agreement with literature δ2 values. δ values were also calculated using only polar or nonpolar probes. The change in δ as the set of probes changed was negligible, leading to the conclusion that Hanson's three‐dimensional solubility parameter concept may not be applicable to the infinite‐dilution case.
The effect of water on the secondary dielectric relaxations in nylon 66
Authors: Starkweather Howard W. , Barkley John R. 
Published: April 2003

AbstractDielectric data were taken on nylon 66 at several moisture levels at frequencies from 10 to 105 Hz and temperatures from −70°C to room temperature. Moisture increases the frequency and the peak height for the β relaxation and reduces its activation energy. The peak height of the γ relaxation is reduced by moisture and shifts to slightly higher frequencies with little change in activation energy. The β relaxation follows the pattern of Jonscher and Ngai for a cooperative many‐body process. The γ relaxation is slightly broader than a Debye relaxation and approaches that model quite closely as the temperature is increased. The high‐frequency end of the β relaxation overlaps the γ relaxation.
Aggregation studies of vinyl chloride and acrylonitrile‐containing copolymers
Authors: Nebenzahl L. , Holleran R. , Milder R. 
Published: April 2003

AbstractThe aggregation properties of two commercially available copolymers of vinyl chloride and acryionitrile are studied using viscometry, membrane osmometry, and low‐angle laser light‐scattering photometry in dimethylformamide and dimethylsulfoxide solvents. Firm evidence of extensive aggregation is found.
Lyotropic mesomorphic formation of cellulose in trifluoroacetic acid‐chlorinated‐alkane solvent mixtures at room temperature
Authors: Patel D. L. , Gilbert R. D. 
Published: April 2003

AbstractMixtures of trifluoroacetic acid (TFA)‐1,2‐dichloroethane (1,2‐DCE); TFA‐dichloromethane (CH2Cl2); and TFA‐trichloromethane (CHCl3) are excellent cellulose solvents at room temperature. TFA‐1,2‐DCE and TFA‐CH2Cl2 are superior to pure TFA. Lyotropic cellulose mesophases were obtained in (20% w/v) solutions of cellulose in these solvent mixtures. The optical and optical rotatory powers of the solutions suggest that the lyotropic mesophase of cellulose is cholesteric. This implies that cellulose molecules are arranged in helical form in these solvent systems.