bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mechanical properties of methanol crazes in poly(methyl methacrylate)
Authors: Kramer Edward J. , Krenz Heider G. , Ast Dieter G. 
Published: April 2003

AbstractMethanol crazes are grown from sharp cracks in poly(methyl methacrylate) (PMMA). The craze thickness profile is measured using a replica technique after the craze opening displacement profile of the growing craze has been measured with holographic interferometry. The craze strain profile is then computed from these data. The craze surface stress profile is determined by two methods: (1) from the uniaxial strain profile of regions adjacent to the craze as measured from the fringe spacing on the reconstructed hologram and (2) from the craze opening displacement profile using the Fourier transform method of Sneddon. From the surface stress and craze‐strain profiles a true stress‐strain curve for the craze fibrils has been constructed. The extrapolated fibril yield stress is in good agreement with the yield stress of bulk PMMA plasticized with methanol indicating that surface tension effects do not contribute importantly to craze fibril mechanical properties at room temperature. The craze strain increases from 0.4 near the craze tip to 1.4 near the craze base implying that methanol crazes in PMMA thicken by further straining of the existing craze fibrils and not by drawing new material into the craze from the craze surfaces. The primordial craze thickness, i.e., the original thickness of polymer which fibrillates to form the craze fibrils, is approximately 1 μm and is constant over most of the craze length. This thickness may be determined by diffusion of methanol normal to the craze surfaces in a process zone just behind the craze tip.
Synthesis and properties of a new polydiacetylene: Poly[1,6‐di(N‐carbazolyl)‐2,4‐hexadiyne]
Authors: Yee K. C. , Chance R. R. 
Published: April 2003

AbstractThe solid‐state synthesis and properties are reported for a new polydiacetylene: poly[1,6‐di(N‐carbazolyl)‐2,4‐hexadiyne]. The monomer crystals polymerize quantitatively with γ irradiation or thermal annealing. An Autocatalytic effect is observed in both γ‐ray polymerization and thermal polymerization and is attributed to an increase in chain propagation length at about 5% conversion. The activation energy for thermal polymerization is about 25 kcal/mole, independent of the degree of conversion to polymer. The exceptional thermal stability of the polymer crystals allowed a thermomechanical analysis over a large temperature range, −50 to 300°C. With increasing temperature, the polymer contracts in the chain direction linearly with temperature over the entire range, yielding a thermal expansion coefficient of (−2.32 ± 0.02) × 10−5°C−1. Photoconductivity action spectra are reported for the polymer crystals. The energies for the photoconductivity onset (ca. 2.3 eV) and for the lowest energy optical transition (1.89 eV) are the lowest reported for the polydiacetylenes. The photoconduction onset is blue‐shifted with respect to optical absorption—a result which is consistent with the excitonic assignment for the lowest energy optical transition in the polydiacetylenes.
Orientation and molecular dynamics in uniaxial polymers. I. Theory of fluorescence polarization
Authors: Jarry J. P. , Monnerie L. 
Published: April 2003

AbstractA theory of polarized fluorescence is developed for uniaxial physical systems in which micro‐Brownian motion is not negligible. All experimental information is shown to reduce, with reasonable assumptions, to four quantities characterizing molecular orientation and reorientational molecular mobility. The geometrical properties of the mobility in uniaxial systems are studied and methods are given for correcting for the effects of the birefringence and for a possible delocalization of the fluorescence transition moments.
Dynamics of a polymer attached to a surface: Bead and spring model
Authors: Dimarzio Edmund A. , Rubin Robert J. 
Published: April 2003

AbstractThe Smoluchowski formalism is used to solve the problem of a bead of frictional resistance β attached to a surface with a spring of force constant k over which a linear shear field of strenght α flows. The power dissipation is given by βα2kT/k. k and T have their usual meanings. The result is generalized to an n‐bead polymer. It is found that the power dissipation of a Rouse model polymer attached to a surface at one end is twice that of an identical polymer flowing freely in solution. If the force constant k arises from an entropy force, then, because of the effect of the surface on the number of polymer configurations, there is an additional factor of two. The same relationship is expected to also hold for the frequency‐dependent power dissipation. It is argued that a net circulation exists in the beads above the surface and that the magnitude of the circulation is roughly comparable to that which exists in a polymer freely rotating in solution under a shear field of the same magnitude.
Chain rupture and tensile deformation of polymers
Authors: Stoeckel T. M. , Blasius J. , Crist B. 
Published: April 2003

AbstractMacromolecular chain rupture occurring during tensile deformation of semicrystalline polymers has been investigated by measuring changes in the viscosity‐average molecular weight. When interpreted in terms of a random‐scission scheme, the observed changes in molecular weight correspond to chain rupture concentrations β ≈ 1018/cm3for high strength nylon and poly(ethylene terephthalate) fibers. Polypropylene fibers and isotropic samples of polyethylene, polypropylene, and nylon 6 had β ≈ 1016/cm3. The effects of stretching environment and thermal and mechanical history were noted. In all cases, the present study indicated bond rupture concentrations about 10 times larger than those obtained from electron spin resonance (ESR) experiments. The relation between viscometry, ESR, and infrared (IR) estimates of bond rupture and their relevance to mechanical properties are considered.
Conformational transition of copolymer of maleic acid and styrene in aqueous solution. III
Authors: Ohno Nobumichi , Okuda Toshihiko , Nitta Katsutoshi , Sugai Shintaro 
Published: April 2003

AbstractKinetic studies of the pH‐induced conformational transition of the hydrophobic copolyelectrolyte of maleic acid and styrene in aqueous NaCl at ionic strength 0.09 were performed by an optical method at 25.0°C with a rapid reaction analyzer of high resolving power. A pH jump applied to a solution, in which the molecule is in the compact form, gives a kinetic trace from which, by appling the general kinetic theory of cooperative transitions, two mean relaxation times are determined. Plots of these relaxation times against the degree of ionization of the primary carboxyl groups of the maleic acid units agree well with theoretical predictions from the linear Ising model, where the molecule in the compact form is described as a random coil with hydrophobic “pockets.” The initiation parameter for a pocket obtained from the kinetic data is 0.036. On the other hand, the parameter calculated from the previous pH‐titration results by applying Zimm–Rice theory is 0.015 at the ionic strength 0.09 and 25.0°C. Such values are compared with those determined from pH‐titration data on other hydrophobic polyelectrolytes.
Ion clustering in a butadiene, styrene, 4‐vinylpyridine terpolymer crosslinked by coordination with iron(III) chloride
Authors: Meyer C. T. , Pineri M. 
Published: April 2003

AbstractA butadiene, styrene, 4‐vinylpyridine terpolymer has been crosslinked by coordination of the pyridine groups with iron chloride. The distribution and structure of the iron complexes have been studied. Electron microscopy has given evidence of clustering of the iron complexes. The size distribution of these clusters has been evaluated by small‐angle x‐ray and neutron scattering. Mössbauer spectroscopy and magnetization measurements have shown the presence of three different kinds of iron complexes: (a) complexes with a speromagnetic structure in the clusters previously found, (b) dimers with antiferromagnetic coupling, and (c) quasi‐isolated complexes with weak ferromagnetic coupling. The percentages of these different iron complexes have been measured.
Non‐Newtonian flow curves including lower and upper Newtonian regions for dilute and moderately concentrated polystyrene solutions
Authors: Ito Yoshio , Shishido Shunsuke 
Published: April 2003

AbstractThe non‐Newtonian viscosity in steady flow was measured for solutions of polystyrene (M̄w/M̄n= 1.1) in diethyl phthalate at 30.0°C. In the moderately concentrated solutions, from 6.03 × 10−2to 5.62 × 10−1g/cm3, the viscosity data modified by frictional parameters fit the Graessley theoretical curve for a narrow distribution polymer. The dilute solutions, from 3.26 × 10−3to 1.57 × 10−2g/cm3, were nonentangled systems whose non‐Newtonian properties could be explained by the excluded volume effect as proposed by Fixman. On the basis of the non‐Newtonian data, it was concluded that the solution of 3.30 × 10−2g/cm3was a lower critical entanglement concentration, which was distinguished from the usual higher critical concentration for entanglement. This lower critical concentration was also found in the concentration dependence of the activation energy of flow and the absorbance at 310 nm.
Diffusion of cyclodextrins in aqueous polymer solutions
Authors: Iijima Toshiro , Uemura Toshinobu , Tsuzuku Susumu , Komiyama Jiro 
Published: April 2003

AbstractDiffusion of α and β cyclodextrin (α‐CD and β‐CD, respectively) has been studied in aqueous solutions of poly(methacrylic acid), sodium poly(styrene sulfonate), having three different degrees of sulfonation (DS), and copoly(styrene‐methacrylic acid) containing three different amounts of styrene. N‐Acetylglucosamine and raffinose were included as reference diffusants. It was found that a decrease of the diffusion coefficients of the CD's in these polymer solutions is characteristically dependent on the polymer concentration, DS, Styrene content, and the degree of neutralization. The results were interpreted by assuming a 1:1 complex formation between CD and an appropriate residue in the polymer. The complex diffusion behavior of CD in the copolymer solutions suggested that the ability of the polymer residue to form complexes with the CD is lost when the polymer chain dimensions are reduced with decreasing neutralization.
Influence of wetting properties of the liquid on environmental stress cracking of polyethylene at high stress
Authors: Shanahan M. E. R. , Schultz J. 
Published: April 2003

AbstractIt has previously been shown that, under high stress and consequently at short times to failure, a major factor governing the environmental stress cracking (ESC) of polyethylene is the ability of a liquid environment to penetrate a growing fissure at a sufficiently high speed to maintain contact with the fracture front. In this earlier study, viscosity was shown to play a significant role in this kinetic effect. The purpose of the present paper is to demonstrate that another property of the solid–liquid system influencing ESC under these high stress conditions is the spreading coefficient of the liquid on the polymer—the parameter defining the tendency of the liquid to wet the polyethylene. It has been shown that the spreading coefficient can be considered as a force and this force in conjunction with atmospheric pressure constitutes the force necessary to drive the liquid into the growing crack.
Single crystals of cellulose II
Authors: Buleon A. , Chanzy H. 
Published: April 2003

AbstractRibbon‐like lamellar single crystals of cellulose II are grown from dilute aqueous solution of cellulose triacetate (number‐average degree of polymerization (DP)‐15) by deacetylation and consequent precipitation. The best results are obtained with methylamine as the deacetylation reagent at 90°C. Electron diffraction indicates the (110) planes to be the growth face. Twin growth occurs frequently with (110) as the twinning plane.
Thermodynamics of nematic phases formed from semiflexible chain polymers
Authors: Krigbaum W. R. , Salaris Franco 
Published: April 2003

AbstractIn co[poly(ethylene terephthalate)‐p‐oxybenzoate] containing 30 mole % oxybenzoate units, the ethylene terephthate units crystallize. The copolymer melts in the temperature range 180–210°C to form a nematic phase which, at a higher temperature, transforms to an isotropic liquid. The latent heat of the first transition is 5 cal/g, and the thermodynamic melting temperature, 247°C, is essentially that expected for a random copolymer of this composition. The nematic → isotropic transition occurs at 244°C, with an enthalpy change of 3.2 cal/g (10% of the heat of fusion of poly(ethylene terephthalate)). We conclude that semiflexible polymers form a nematic phase which is rather highly disordered. The model of the nematic phase treated by Flory is modified to increase its entropy through incorporation of chain bends (which must be correlated in position and direction with those in neighboring molecules). This increases the chain extension, as measured by the fraction (1–f) of collinear chain bonds, required to form the nematic phase. For binary polymer‐solvent systems, an appropriate scaling of f values leaves the phase diagram as predicted by Flory's treatment essentially unchanged.
Dielectric properties of oligomers. VI. End‐group effects in vinyl acetate and methyl methacrylate oligomers
Authors: Ikada E. , Sugimura T. , Watanabe T. 
Published: April 2003

AbstractDielectric properties of vinyl acetate and methyl methacrylate oligomers having chemically different end groups were compared. Dielectric measurements were carried out over the frequency range between 23 and 3 MHz and the temperature range between +50 and −50°C. The static dielectric constants of these oligomers are between 10 and 20. The relaxations were analyzed with the Havriliak–Negami equation. The dielectric properties depend on the chain end groups on the oligomers. The distribution of relaxation times of the vinyl acetate oligomers was wider than that of poly(vinyl acetate). It was concluded that two cooperative motions, that of the principal chain and that of the chain and that of the chain end group, take part in the dielectric relaxation of these short chain molecules.
Combined constant strain rate and stress relaxation test for linear viscoelastic studies
Authors: Meissner Joachim 
Published: April 2003

AbstractThe strain history of the combined test is formed by a constant strain rate during the period 0 <t < t1 followed by a constant strain for t > t1. This test includes as limiting cases the relaxation test (t1 → 0), the constant strain rate or stress growth experiment (t1 → ∞), and the stress relaxation after cessation of constant strain rate flow (t1 sufficiently large). The constant t1 can be chosen arbitrarily such that the test conditions of the combined test can be adjusted according to the problem investigated and to the capability of the testing device. From this, practical advantages follow for linear viscoelastic studies of polymeric solids and liquids, e.g., the zero shear viscosity η0 for unstable polymer melts can be determined at least approximately. In order to obtain linear viscoelastic material functions from the measured stress record, a simple procedure is given which avoids the difficulties with the “factor‐of‐10 rule” for short relaxation times.
Properties of vinylpyrrolidone‐tert‐butylphenyl methacrylate copolymers in solution
Authors: Radic Deodato , Gargallo Ligia 
Published: April 2003

AbstractCopolymers of vinylpyrrolidone‐p‐tert‐butylphenyl methacrylate (VP‐MBPh) of several compositions were prepared by polymerization in benzene at 50°C using α′α′‐azobisisobutyronitrile as initiator. Three of the copolymers were fractionated. Number‐average molecular weights of fractionated samples were determined by osmotic pressure in benzene or 2‐propanol. Kuhn–Mark–Houwink relations were established in benzene, chloroform, and 2‐propanol. From the relation between Mn and the intrinsic viscosity (η), it appears that these random copolymers behave as predicted by the theory for flexible polymers. Abnormal viscometric behavior shown by one of the copolymers in nitromethane at 29°C (the theta temperature) is discussed. The Stockmayer–Fixman semiempirical method was used for estimating unperturbed dimensions from viscosity data obtained in chloroform, a good common solvent. Values of the viscosity parameter Kθ increase with the content of p‐tert‐butylphenyl methacrylate. In general, experimental Kθ values are higher than those calculated for the homopolymers. Excluded‐volume parameters are estimated and discussed in relation to repulsive interactions between unlike monomer units.
Intrinsic viscosity and translational friction coefficient of nondraining flexible rings with small excluded volume
Authors: Norisuye Takashi , Fujita Hiroshi 
Published: April 2003

AbstractFirst‐order excluded‐volume effects on the intrinsic viscosity and translational friction coefficient of nondraining flexible ring polymers were calculated on the basis of the Kirkwood–Riseman formalism of polymer hydrodynamics. The cube of the viscosity expansion factor αη,r was found to be represented by α = 1 + 1.18z + …, where z is the usual excluded‐volume parameter. Combination of this result with the corresponding calculation by Fujita et al., for nondraining linear polymers, yielded α/α = 1 – 0.11z + … (αη,l denotes the viscosity expansion factor for linear chains). The negative coefficient of the z term contradicts the conclusion by Tanaka and Yamakawa who used the Zimm–Hearst theory of polymer dynamics. The friction expansion factor αf,r, for ring polymers, was obtained in powers of z as αf,r/αf,l = 1 + 0.773z + …. The earlier evaluation of αf,r by Fukatsu and Kurata was in error. The ratio αf,r/αf,l (αf,l is the friction expansion factor for linear chains) was given by 1 ± 0.182z ± … when the corresponding result on αf,l was used. This expansion compares well with Casassa's result αs,r/αs,l = 1 ± 0.147z + … for the ratio of the radius expansion factors of ring and linear chains.
Proton spin relaxation in liquid polydimethylsiloxane: Molecular motion and network formation
Authors: Folland R. , Steven J. H. , Charlesby A. 
Published: April 2003

AbstractProton spin relaxation time measurements are reported for a series of liquid polydimethylsiloxanes covering the temperature range from −50 to 200°C. These include fractionated and whole polymer samples (Mw from 104 to 106), binary mixtures, and crosslinked material. This paper is mainly devoted to the behavior of the spin‐spin relaxation (T2) which is sensitive to the low‐frequency long‐range configurational motions occurring in the liquid phase. These motions determine the time scale over which final motional averaging of the nuclear dipolar interactions occur, prior to the onset of normal liquid‐like behavior of T2. When these motions are too slow (e.g., at low temperatures of high molecular weight) to lead to appreciable averaging of the small residual static dipolar interactions present in the liquid phase, the spin‐spin relaxation exhibits pseudo‐solid‐like behavior. A further aspect of this work concerns the observed sensitivity of T2 to network formation which considerably restricts the long‐range motions that determine T2. It is possible to determine the fraction of material present in the form of a network from the relative proportions of network and non‐network T2 components. This is not only true for a permanent crosslinked network but also for a network arising from transient entanglement couplings. The dynamic nature of the latter type of a network is clearly revealed in the proton nuclear magnetic resonance measurements reported here.
An equation for creep in terms of craze parameters
Authors: Brown Norman , Metzger Bruced D. , Imai Yasufumi 
Published: April 2003

AbstractThe creep curves of poly(chlorotrifluoroethylene) (PCTFE) and poly(methyl methacrylate) (PMMA) were measured at temperatures near 78°K in nitrogen environments so that practically all the creep strain was produced by crazing. Data were obtained over a range of temperatures, stresses, and partial pressures of the nitrogen. It was found that all creep curves had the form, ε1/3= ε+st, where ε0is the initial strain (∼10−4) andsis a constant which depends on the conditions of the test. The microparameters such as number, dimensions, and velocity of the crazes were measured in each speciman. A theoretical creep equation was derived in terms of these microparameters. There was good quantitative agreement between theory and the experiments.
Rubber elasticity in the range of small uniaxial tensions and compressions. Results for poly(dimethylsiloxane)
Authors: Erman Burak , Flory Paul J. 
Published: April 2003

AbstractResults of uniaxial tension and compression experiments are reported on crosslinked polydimethylsiloxane (PDMS) networks in the unswollen state over the range 0.5 < α−1 < 1.2 where α is the extension ratio. Curves representing the reduced force [f] = f(V0/V)1/3(α – α−2)−1 plotted against α−1 can be approximated by straight lines for 0.5 < α−1 < 0.9, in agreement with the phenomenological Mooney equation. As α−1 approaches 1, however, they tend to level off and continue into the α−1 > 1 region with decreasing slope. These results are in agreement with the predictions of recent elasticity theories that incorporate the effect of junction‐chain entanglements in the elastic free energy.
Volumetric properties of dilute aqueous solutions of poly(ethylene glycols)
Authors: Lepori Luciano , Mollica Vincenzo 
Published: April 2003

AbstractThe densities of aqueous solutions of some poly(ethylene glycols) (mono‐, di‐, tri‐, and tetraethylene glycol, and four carbowaxes with a mean molecular weight ranging from 600 to 15,000), and of di‐, tri‐, and tetraethylene glycol dimethyl ether have been determined at 25°C, in the concentration range 5–100 g/liter. From these data, the limiting partial specific and/or molar volume of the solute has been calculated. A value of 37.0 ml/monomole has been evaluated for the partial molar volume of the repeating unit CH2CH2O, and has been found independent of both terminal groups and chain length. The results suggest that the ethylene units in higher polymers are accessible to the solvent as easily as in oligomers, and support an “open” or extended conformation of the poly(ethylene glycol) chain in aqueous dilute solution. This interpretation has been confirmed by a comparison of the experimental values of partial molar volume with the values calculated by semiempirical models.