bluuebunny/crossref_metadata_2025 huggingface dataset:
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

Elastomeric 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

X‐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

Resonance 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

Molecular 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

The 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

A 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

The 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

Correlations 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

Intrinsic 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

Brillouin 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

A 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

Dielectric 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

Work 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

Crosslinked 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

Films 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

Polarized 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

The 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

Partial 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

Dielectric 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

The 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

Mixtures 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.
Molecular aggregation of solid aromatic polymers. I. Small‐angle x‐ray scattering from aromatic polyimide film
Authors: Isoda Satoru , Shimada Hiromichi , Kochi Masakatsu , Kambe Hirotaro
Published: April 2003

Molecular aggregation in a commercial polyimide film, Du Pont Kapton, was investigated by small‐angle x‐ray scattering (SAXS). From the analysis of the desmeared SAXS curve, it is concluded that aggregation in the Kapton film can be elucidated in terms of a two‐phase structure having electron density fluctuations within the phases. For comparison with the molecular aggregation in Kapton, molecular aggregation in polyimides synthesized in our laboratory was also investigated. It was found in this case that molecular aggregation is controlled by the initial imidization temperature. Molecular aggregation of polyamic acid and polyimide cyclized at a low temperature gives amorphous structures. On the other hand, molecular aggregation of polyimide cyclized at high temperatures gives two‐phase structures like that of Kapton film. The SAXS curve for a polyimide having the two‐phase structure shows a peak due to interference between ordered regions. The two‐phase structure of the polyimide can be explained in terms of a one‐dimensional model. The more ordered phase is produced at the higher initial imidization temperature. The relative density difference between two phases is only a few percent for polyimide films cyclized at high temperatures. This result shows that the two‐phase structure of aromatic polyimide differs essentially from that of ordinary crystalline polymers.
DTA and x‐ray studies on extended‐chain crystals of polyethylene under high pressure
Authors: Maeda Yoji , Kanetsuna Hisaaki , Tagashira Katsuharu , Takemura Tetuo
Published: April 2003

The relation between the thermal behavior of extended‐chain crystals (ECCs) of polyethylene and the phase transitions, i.e., orthorhombic ↔ hexagonal ↔ melt, of polyethylene at high pressures above about 400 MPa has been studied by high‐pressure differential thermal analysis (DTA), and with a high‐pressure and high‐temperature x‐ray diffraction apparatus equipped with a position‐sensitive proportional counter measuring system. The original sample used in this study consists mainly of two kinds of ECC, which we designate as “ordinary extended‐chain” crystals (OECCs) and “highly‐extended‐chain” crystals (HECCs). Experimental results at pressures below 300 MPa substantiate the results previously reported: i.e., the phase diagram indicating the relation between the melting temperatures and pressure for the OECCs and HECCs can be determined for pressures up to 500 MPa.

In heating at pressures above about 500 MPa, the peak intensity of the (100) reflection of the hexagonal structure decreases in two stages with increasing temperature. The phenomenon corresponds to the thermal behavior determined by high‐pressure DTA in which two small endothermic peaks can be observed at temperatures above that of the crystal transition evidenced by the strong peak. This phenomenon suggests melting in two stages of hexagonal structures with different thermal stabilities, and that the change at higher temperature may be due to fusion of the hexagonal phase annealed either below or above the transition temperature.
Column fractionation of acrylonitrile‐styrene copolymers
Authors: Ogawa Toshio , Sakai Masakazu
Published: April 2003

An acrylonitrile‐styrene copolymer having 51.4 wt % acrylonitrile content was fractionated using dimethylformamide and a toluene–n‐propanol mixture as solvent and nonsolvent, respectively. From characterization of the fractions, it is shown that the copolymer was fractionated principally in accordance with composition. The weight distribution curve of the copolymer was expressed as a function of both molecular weight and chemical composition on a two‐dimensional contour map. The same plotting technique was applied to a copolymer having nearly the azeotropic composition.
NMR study of the demixing process in concentrated polyisobutylene solutions
Authors: Cohen‐Addad J. P. , Roby C.
Published: April 2003

A study of the magnetic resonance linewidths of the polymer protons of the polyisobutylene toluene system is presented as a function of concentration c and temperature T. Two distinct regions are observed in the linewidth versus concentration or temperature curves. A phase diagram is constructed, one region of which exhibits characteristic NMR properties supposed to reflect microphase separation of polymer and solvent. The demixing curve derived from NMR measurements is expressed by c = 11.3(267–T). The θ temperature of this system is 260 K.
Craze initiation in poly(methyl methacrylate) under biaxial stress
Authors: Kawagoe M. , Kitagawa M.
Published: April 2003

Criteria for craze initiation in poly(methyl methacrylate) have been investigated under various combined loadings including biaxial tension and torsion‐compression at 65°C in air and at room temperature in a crazing agent, kerosene. Environmental crazes are observed even under torsion‐compression loading when air crazing does not occur, and the stress locus for environmental crazing is very different from that for air crazing. A theoretical model analogous to the Cottrell model in crystal plasticity is proposed. Theoretical crazing loci derived from the model are compared with the experimental results.
Morphology of oriented linear polyethylene: A study by Raman spectroscopy
Authors: Capaccio G. , Wilding M. A. , Ward I. M.
Published: April 2003

Measurements have been made of the low‐frequency Raman longitudinal acoustic mode (LAM) vibration in oriented linear polyethylenes. The oriented samples were prepared by tensile drawing of both slow‐cooled and quenched sheets, and included ultrahigh‐modulus materials from draw ratios up to 30. A LAM line is observed clearly in samples of low and intermediate molecular weight up to draw ratios of ca. 15. In all these cases the Raman spectrum has been used to calculate the whole distribution of crystal sizes. This procedure leads to values of the number‐average and weight‐average crystal size which are in good agreement with crystal size determinations by x‐ray diffractometry and gel permeation chromatography on etched samples. At higher draw ratios the peak intensity of the LAM line is diminished. This can be attributed to a change in the distribution of crystal thicknesses, consistent with data from x‐ray diffraction and nitric acid etching. Effects due to initial morphology, sample molecular weight, and draw temperature have also been examined.
Carbon‐13 NMR of poly(vinyl acetate) and ethylene–vinyl acetate copolymer
Authors: Sung H. N. , Noggle J. H.
Published: April 2003

Carbon‐13 nuclear magnetic resonance spectra of atactic poly(vinyl acetate) and ethylene–vinyl acetate copolymers are reported and analyzed. Carbon spectra at 22.6 and 62.9 MHz together with use of shift reagents have permitted a more complete assignment than previously reported; in some cases the published assignments are found to be in error.
Stress–strain behavior of randomly crosslinked polydimethylsiloxane networks
Authors: Gottlieb M. , Macosko C. W. , Lepsch T. C.
Published: April 2003

The stress–strain behavior of randomly crosslinked polydimethylsiloxane (PDMS) networks was studied. The small‐strain data obtained agreed well with available data on radiation‐crosslinked PDMS networks. It was found that both the suppression of junction fluctuation and trapped entanglements have to be considered in order to account for the discrepancy between experimental data and the phantom‐network theory. With the addition of a constant trapped entanglement term, Flory's recent network model describes correctly the behavior of our networks under tonsion and compression. The values of the parameters used in fitting the data are within the range suggested by Flory for typical rubber networks. Edwards' “potential pipe” theory did not correlate our data over the entire range of strain variation.
Structure and properties of charge‐mosaic membranes from modified polyethylene. I. Preparation and characterization
Authors: Gajek Ryszard , Trochimczuk Witold
Published: April 2003

Charge‐mosaic membranes (CMMs) were prepared by modification of polyethylene (PE) with poly(styrene‐co‐divinylbenzene) or poly(vinylpyridine‐co‐divinylbenzene) and by selective insertion of cation and anion exchange groups in these copolymers. Changes of divinylbenzene content in the monomer mixture gave rise to differences in transport properties mainly through the change in water content. The CMMs were characterized by physico‐chemical properties of control membranes, i.e., they contained only one type of modified PE. Values were similar to those obtained from measurements carried out for CMMs. Diffusion coefficients determined in 0.1/0.02N NaCl solutions were in the range (1.5‐–5.7) × 10−7 cm2s−1. These values indicate that transport of salt through these CMM's occurs by a typical mechanism for such membranes.
Random‐coil configurations of the polyformals. VI. Dipole moments of the stereochemically variable polymer prepared from 4‐methyl‐1,3‐dioxolane
Authors: Riande E. , Garcia M. , Mark J. E.
Published: April 2003

Mean‐square dipole moments 〈μ2〉0 for the (atactic) poly(4‐methyl‐1,3‐dioxolane) chain [CH2OCH(CH3)CH2O] were determined from dielectric‐constant measurements carried out on two fractions dissolved in benzene. Simple examination of the chain structure leads to the predictions that this polymer should have a significantly larger value of 〈μ2〉0 than poly(1,3‐dioxolane) itself, but that 〈μ2〉0 should be nearly independent of stereochemical structure. The first expectation is confirmed by the experimental results obtained, and the second by calculated results based on rotational isomeric state theory.
A structure with an irregular layer lattice in poly(γ‐methyl L‐glutamate‐co‐γ‐benzyl L‐glutamate) film
Authors: Watanabe Junji , Gehani Ramesh , Uematsu Ichitaro
Published: April 2003

Two types of films showing different characteristic x‐ray equatorial patterns were prepared from chloroform and N,N‐dimethylformamide solutions of poly(γ‐methyl L‐glutamate‐co‐γ‐benzyl L‐glutamate). In the film cast from chloroform solution, the x‐ray pattern on the equator consisted of a remarkable mixture of sharp and diffuse reflections, with the sharp reflections corresponding to integral values of 1/3k. On the other hand, in the film cast from N,N‐dimethylformamide solution, a well‐defined x‐ray pattern was observed. An explanation for this characteristic pattern of chloroform‐cast film was made on the basis of a structural model wherein stacking faults or dislocations are incorporated into the ordered structure characteristic of N,N‐dimethylformamide‐cast film. Two domains divided by a stacking fault are mutually displaced along the (100) crystal planes, but the shape and size of the unit cell is everywhere the same. The intensity distribution of x‐ray diffraction was calculated as a function of the probability of a stacking fault occurring in a regular sequence of (100) planes. The best correspondence with observation was obtained with a stacking fault in every three layers, on the average.
Epitaxial crystallization of aliphatic polyesters on trioxane and various aromatic hydrocarbons
Authors: Wittmann J. C. , Lotz B.
Published: April 2003

Linear polyesters of the diacid‐dialcohol type are observed to crystallize epitaxially onto substrate crystals of trioxane, condensed aromatic hydrocarbons, and linear polyphenyls. In line with results previously reported for PE, lattice matching requirements for epitaxy lead to a change in the polymer contact plane on the different substrates. The highly oriented, sometimes single‐crystal‐like polymer films are formed of stacks of lamellae seen edge on which appear well suited to investigations of the lamellar structure.
Small‐angle X‐ray scattering of isotactic poly(4‐methyl‐1‐pentene)
Authors: Tanigami Tetsuya , Miyasaka Keizo
Published: April 2003

Although the crystalline phase of poly(4‐methyl‐1‐pentene) (P4MP) is less dense than the amorphous phase, the density difference is very small at room temperature. This makes it difficult to study the fine structure of P4MP by small‐angle x‐ray scattering (SAXS). It has therefore not been clear whether a so‐called superlattice, or long‐spacing structure, is formed in P4MP as in other synthetic polymers. However, it is found that raising the temperature increases the density difference sufficiently to make SAXS study feasible, and the existence of the long‐spacing structure of P4MP is indicated. Annealing studies reveal two characteristic temperatures of 170 and 200°C: above 170°C the long‐spacing structure is formed with an abrupt increase of crystallinity, and at 200°C the structure is further developed.
Dual‐mode sorption and transport of sulfur dioxide in kapton polyimide
Authors: Felder R. M. , Patton C. J. , Koros W. J.
Published: April 2003

The kinetics and equilibria of SO2 sorption in Kapton polyimide film have been studied at temperatures from 25 to 55°C and equilibrium sorption pressures up to 0.76 atm. The data are described well by the dual‐mode model of sorption and transport in glassy polymers. The assumption of “partial immobilization” is required to correlate the transport data: the mobility of the Langmuir component of the sorbed population relative to the Henry's‐law component is close to zero at 25°C, and increases to roughly 5% of the Henry's‐law component mobility at 55°C. The heat of sorption is anomalously low, suggesting the presence of residual solvent in the film, a suggestion confirmed by annealing studies. However, the study also shows that partial removal of the residual has a relatively minor effect on the measured SO2 sorption level and transport rates at 55°C.
Effect of disorder in the twist angle on light scattering by a three‐dimensional spherulite
Authors: Matsuo Masaru , Ihara Kumi
Published: April 2003

Light scattering patterns are calculated for imperfect three‐dimensional spherulites with fluctuations in the twist angle. The fluctuations are described in terms of a parameter characterizing the distance correlation function. Cases are considered in which (i) the principal axis of the scattering element makes a constant angle with the radius but there is disorder in the twist angle about the axis, and (ii) there is combined twist disorder and orientation disorder of the scattering elements. Calculations suggest that the disorder in the twist angle may lead to a decrease in the higher‐order variation of scattered intensity with scattering angle and deviation from the four‐leaf‐clover‐type scattering characteristic of a perfect spherulite at lower scattering angles. On the other hand, disorder in orientation has little effect on the scattering pattern.
The nature of the nonlinear anelasticity of glassy polymers
Authors: Boyd R. H. , Robertsson M. E. , Jansson J. F.
Published: April 2003

Nonlinearity in stress‐strain behavior under conditions where the strain is completely recoverable is often observed in glassy amorphous polymers. In the present work a suggestion is made that the nonlinearity is often associated with a secondary (β) relaxation process. By means of a model calculation it is shown that the onset of stress saturation of the relaxed or equilibrium compliance associated with localized group motion is a reasonable explanation for the phenomenon. The effect of stress on relaxation times is predicted to have some contribution but to be less important than the effect on the relaxed compliance.
Concentrated solution viscosities of polymeric associates
Authors: Worsfold D. J.
Published: April 2003

Reasons have been advanced why in some cases concentrated‐polymer‐solution viscosity measurements are not a suitable method for determining the degree of association of groups attached to polymer chains. These are based on the finite lifetimes of associates compared with the finite lifetimes of the entanglements, which are the major contributors to concentrated‐polymer‐solution viscosities. The validity of these reasons has been checked in a system where the degree of association of polymer chains can be measured spectroscopically. It was found that the viscosity of these solutions was considerably less than that calculated by the concentrated‐solution viscosity equation for solutions of polymers of the average molecular weight expected from the spectroscopically found degree of association.
Wide‐angle neutron scattering studies of mixed crystals of polyethylene and deuteropolyethylene
Authors: Wignall G. D. , Mandelkern L. , Edwards C. , Glotin M.
Published: April 2003

Wide‐angle neutron scattering studies have been made of a series of mixed crystal blends of polyethylene and deuterated polyethylene in the range 0.68 ≤ K = 4πλ−1 sinθ ≤ 2.02 Å−1. Recent calculations by Stamm have shown that regularly folded subunits of small numbers (two to ten) of stems should produce an observable modulation of the diffuse scattering pattern of such mixtures in this K range. For both melt‐ and solution‐crystallized blends, no extra signal was observed above the background scattering level. The data are used to place an upper limit (of about four) on the number of stems that could be regularly folded in the (100) and (010) planes for these materials.
Melt rheology of ion‐containing polymers. I. Effect of ionic content in a model polyesterionomer
Authors: Connelly R. W. , McConkey R. C. , Noonan J. M. , Pearson G. H.
Published: April 2003

The effects of copolymerizing small amounts of an ionic moiety (0–7 mol %) into the backbone of a polycondensation polymer have been investigated by a combination of linear viscoelastic, steady‐shear, and extensional testing. At a constant viscosity in dilute solution, both the zero‐shear‐rate viscosity and the maximum relaxation time in the melt increase monotonically with an increase in the ionic character. These effects are present after the data are normalized to remove the increase in the glass transition temperature Tg with increased ionic content. Large‐strain, steady‐shear flow experiments showed that the viscoelastic memory of the melt is affected by ionic content. An increase in ion content causes a decrease in the effect of strain on the memory function. This effect is not apparent in extensional flow experiments, which indicate that the ionic content does not affect the response if the tests are conducted at a constant temperature above Tg.
Improved calorimetric procedure for monitoring the approach to thermodynamic equilibrium in glassy polymers
Authors: Lagasse R. R.
Published: April 2003

Techniques for measuring the enthalpy change during isothermal aging of polymer glasses are discussed. Critical analysis of conventional scanning calorimetry reveals that its accuracy may be suspect under certain circumstances due to the thermal lag inherent in a temperature scanning experiment. An additional problem is that the conventional technique is restricted to certain kinds of paths for reaching the aging temperature. It is proposed that both problems can be overcome by analyzing the output of a scanning calorimeter not only during steady heating but also during the transients at the beginning and end of a heating scan. This data analysis method represents an extension of a method used previously by others in accurate measurements of the much larger heat of fusion of crystalline polymers. Practical feasibility of the improved technique is demonstrated by preliminary measurements of enthalpy relaxation during aging of well‐characterized polystyrene at 80°C. In particular, the initial departure from equilibrium of a glass prepared by 5°C/min cooling from the liquid state is found to be 6.9 ± 0.6 J/g. This measured value agrees with a value calculated on the basis of the glass transition temperature corresponding to 5°C/min cooling and heat‐capacity data from the literature.
Studies of tensile failure in oriented polymeric fibers by quantitative fractography
Authors: Lamb George E. R.
Published: April 2003

For some fibers, such as the nylon monofilaments studied here, quantitative information may be obtained from scanning electron micrographs of fracture surfaces. On these surfaces the segment of the cross section that supports the load at the instant of rupture is seen distinctly, and its area can be measured. Normalizing breaking load by this area provides a breaking stress characteristic of the final supporting segment. “Ultimate” breaking stresses calculated in this way indicate (i) For notched filaments, the ultimate breaking stress is almost constant with notch depth and also with strain rate. (ii) For un‐notched filaments, there is an increase of breaking load with strain rate, due in part to the extent of the slow cleavage that precedes failure; however, the ultimate breaking stress increases as rate of strain decreases. These two findings are incompatible with mechanisms of failure based on growth of microcracks by heat‐ and stress‐activated chain breakage. A possible explanation involves rearrangement of microfibrils within the fiber which alters their strength distribution. (iii) The apparent strength reduction on wetting nylon filaments in water is due to a faster rate of growth of the slow‐cleavage area; the ultimate breaking stress is unchanged, except at high rates of strain.
Investigation of local order in unreacted DGEBA epoxy resin monomers by light scattering
Authors: Stevens G. C. , Champion J. V. , Liddell P.
Published: April 2003

The existence of local order in two epoxy resins of the diglycidyl ether of bisphenol‐A (DGEBA) type has been investigated using Rayleigh scattering and Brillouin spectroscopy. The resins differ in their molecular weight distributions and their relative concentrations of epoxide and hydroxyl groups. The complementary use of both techniques in elucidating the thermal behavior of local order is illustrated, and the use of the latter technique to study thermal acoustic phonons and hypersonic relaxation is discussed. Both techniques independently show that molecular aggregates exist in each resin system. The scattering‐envelope dissymmetry shows that the resin with the high epoxide/hydroxyl group ratio contains aggregates up to 20 nm in size, and the low‐ratio resin exhibits sizes up to 70 nm. These aggregates are thermally unstable in the temperature range studied (293–443 K). Dissolution in chloroform shows that these aggregates are reduced in size and that further structural changes occur which are dependent on solvent concentration. Aggregate volume fractions were determined for a range of aggregate size. Brillouin spectroscopy indicated that both resins exhibit hypersonic relaxation in the temperature range studied. The complex longitudinal moduli of the resins were superimposable under a WLF temperature transformation comparable to the difference in their static glass transition temperatures. Molecular aggregate size, number, and stability are related to the epoxide/hydroxyl ratio of the resins and the degree of intermolecular hydrogen bonding.
Reduced‐variable mechanical characterization of styrene‐butadiene rubber with varying crosslink density, temperature, and finite strain states
Authors: Arenz R. J. , Landel R. F.
Published: April 2003

A single master logarithmic stress relaxation curve of reduced modulus as a function of reduced time is established for a styrene‐butadiene rubber (SBR) system, accounting for the effects of crosslinking density, temperature, and time. The results from recent tests involving uniaxial and various biaxial strain states at finite strain levels may be represented by a unique strain‐energy function W of the Valanis‐Landel separable symmetric type,

where the λi are principal extension ratios. These two representations demonstrate that the mechanical response of whole families of elastomeric materials may be predicted once a single member of the family is fully characterized.
Characterizing the kinetics of volume recovery in glasses by instantaneous temperature‐jump experiments
Authors: Lagasse R. R. , Cohen R. E. , Letton A.
Published: April 2003

This article proposes a temperature‐jump (T‐jump) approach for characterizing the kinetics of volume recovery in glassy materials. The kinetic characterization is based on the Kovacs‐Aklonis model. This incorporates a retardation‐time spectrum which shifts according to both the temperature and the instantaneous volume. The proposed experiments involve measuring the change in recovery rate caused by an abrupt temperature jump. Although an analogous procedure has been used to determine the activation energy for linear viscoelastic creep, the analysis for volume recovery is complicated by its inherent nonlinearity. Nevertheless, accounting for the nonlinearity by a reduction of the time scale permits the T‐jump results to be analyzed. In particular, the T‐jump approach can be used to: (i) test a particular functional form for the shift factor and (ii) determine the previously unmeasurable parameter x, which defines the relative importance of the temperature dependence and the volume dependence in this function. In addition, numerical simulations indicate that the proposed method can be implemented in the laboratory.
Transient decay studies of photophysical processes in aromatic polymers. V. Temperature dependence of excimer formation and dissociation in copolymers of 1‐vinylnaphthalene and methyl methacrylate
Authors: Phillips D. , Roberts A. J. , Soutar I.
Published: April 2003

The use of pulsed laser excitation upon a series of 1‐vinylnaphthalene/methyl methacrylate co‐polymers in which the intramolecular chromophore concentration is varied over a wide composition range has allowed the individual rate constants governing intramolecular excimer formation to be determined at various temperatures between 205 and 295 K. Triple exponential functions are necessary for adequate description of the photophysical kinetics over the entire temperature range. It is proposed that the kinetic and temperature behavior is consistent with a kinetic scheme involving two kinetically distinct monomeric species and an excimer in which energy may be transferred from the second monomer M*2 to the first monomer M*1 which can interact with the excimer by a conventional migration mechanism.
Determination of branching distributions in polyethylene and ethylene copolymers
Authors: Wild L. , Ryle T. R. , Knobeloch D. C. , Peat I. R.
Published: April 2003

A description is given of an analytical temperature‐rising elution fractionation (TREF) system for the purpose of determining short‐chain branching (SCB) or copolymer distributions in poly‐ethylenes and ethylene copolymers. The system achieves fractionation on the basis of crystallizability and is shown to be very little influenced by molecular weight in the normal high polymer range. Sample preparation by slow cooling from relatively dilute solution followed by continuous elution with a simultaneous and fairly rapid rate of temperature rise proves to be an efficient fractionation process. An on‐line detector and data system allows application of a calibration curve to give realistic SCB distribution data in a convenient manner. The potential value of the TREF technique for providing structural information is illustrated by examples which include low‐density high‐pressure resins made by both tubular and autoclave reactors, high‐ and low‐density resins made by low‐pressure processes, and copolymers of ethylene with vinyl acetate and ethyl acrylate.
Model networks of end‐linked polydimethylsiloxane chains. XIV. Stress‐strain, thermoelastic, and birefringence measurements on the bimodal networks at very low temperatures
Authors: Zhang Z.‐M. , Mark J. E.
Published: April 2003

Bimodal networks consisting of very short and relatively long poiydimethylsiloxane (PDMS) chains were studied from 30 to −52°C in an attempt to elucidate the anomalous increases in modulus [f*] exhibited by such elastomeric materials at high elongations. Temperature was found to have very little effect on (i) the elongation at which the upturn in [f*] becomes discernible, (ii) the elongation at which rupture occurs, and (iii) the total increase in [f*] up to the rupture point. The standard force‐temperature (“thermoelastic”) plots were linear, but gave values of the energetic contribution to the total force which were significantly smaller than those universally obtained on unimodal, long‐chain PDMS networks. Birefringence‐temperature relations were also found to be linear, and yielded values of the optical‐configuration parameter and its temperature coefficient which were in satisfactory agreement with the corresponding values reported for unimodal PDMS networks. These results indicate that even at very low temperatures the observed increases in modulus (and consequent improvements in ultimate strength) are due to non‐Gaussian effects arising from limited chain extensibility, rather than from intermolecular reinforcing effects such as strain‐induced crystallization.