bluuebunny/crossref_metadata_2025 huggingface dataset:
Stress birefringence in amorphous polymers under nonisothermal conditions
Authors: Matsumoto Takayoshi , Bogue Donald C.
Published: April 2003

The relationship of birefringence to stress in an amorphous polymer was studied, with emphasis on conditions of high stress and rapid cooling. The latter (nonisothermal) conditions are important in connection with studies of polymer processing operations. Polystyrene was pulled at a constant elongation rate (0.075 to 2 sec−1 in the present and related work) under both isothermal conditions (in the range 120 to 157°C) and nonisothermal conditions (with cooling rates in the range 0.6 to 1.7°C/sec). Generally we conclude that stress in proportional to birefringence under a wide range of conditions, except that a nonlinear regime appears at stresses higher than about 107 dyn/cm2. In this regime, stress increases more rapidly with deformation than does birefringence.
Physical properties and structure of silk. V. Thermal behavior of silk fibroin in the random‐coil conformation
Authors: Magoshi Jun , Magoshi Yoshiko , Nakamura Shigeo , Kasai Nobutami , Kakudo Masao
Published: April 2003

The thermal behavior of films of amorphous silk fibroin in the random‐coil conformation has been investigated in the temperature range 25–220°C by differential scanning calorimetry (DSC), thermal expansion, dynamic mechanical measurements, x‐ray diffraction, and infrared spectroscopy. As the temperature is raised, water is lost up to about 100°C. Intramolecular and intermolecular hydrogen bonds are broken between 150 and 180°C. The glass transition is observed at 173°C by DSC. The random‐coil→β‐form transition accompanied by reformation of hydrogen bonds takes place above 180°C. Thermally induced crystallization to the β‐form crystals starts at about 190°C.
Shear‐induced β‐form crystallization in isotactic polypropylene
Authors: Dragaun H. , Hubeny H. , Muschik H.
Published: April 2003

Extruded, injection‐molded, unoriented crystallized specimens and capillary rheometer efflux strands of commercially stabilized polypropylene without nucleating agents were examined by optical microscopy and x‐ray diffraction to determine the conditions for β‐form crystallization as a function of the distance from the surface and of the shear rate at commercial processing conditions. Results demonstrate that at all “cooling conditions” ΔT = Tm − Tb (defined as the melt temperature Tm minus the bath temperature Tb) effects of strain flow initiate nucleation of β‐form crystals. The shear rate is demonstrated to be important for β‐form crystallization. A critical average threshold value for the shear rate of approximately 3 × 102 sec−1 has to be exceeded. The β modification is mostly connected with type‐III spherulites and partly to row structures, and it is observed at processing conditions in oriented structures only.
A normal vibrational analysis of isotactic polystyrene
Authors: Painter Paul C. , Koenig Jack L.
Published: April 2003

The regularity bands of isotactic polystyrene are determined using Fourier transform infrared spectroscopy to digitally substract the spectrum of a quenched sample from that of an annealed sample. Crystallization‐sensitive bands in the Raman spectrum are identified by comparison of the spectra of annealed and quenched samples. The normal modes of isotactic polystyrene are calculated using force fields determined for saturated hydrocarbons and alkyl benzenes. A good fit between observed and calculated frequencies is obtained. It is evident from this study that the complex behavior of certain bands in the spectrum is due to a mixing of phenyl and skeletal vibrations.
Preparation and study of separated single crystals of extended‐chain polyethylene
Authors: Czornyj George , Wunderlich Bernhard
Published: April 2003

Etching of extended‐chain crystals of polyethylene is shown to permit separation of the polycrystalline aggregate into single crystals. The single crystals are analyzed by density, molecular weight (lamellar crystal thickness), melting temperature, birefringence, superheating, and linear melting rate determination. The linear melting rate depends linearly on superheating and can be described by simple rate theory.
Structure of styrene–butadiene–styrene block copolymers by diffusion analysis
Authors: Chiang Kwan T. , Sefton Michael V.
Published: April 2003

In this study, solvent sorption was used to investigate the morphology of a styrene–butadiene–styrene (SBS) triblock copolymer. The sorption process was found to deviate from the normal Fickian character, usually found in conventional elastomer–solvent systems, because of the presence of an interfacial region for both polybutadiene and polystyrene. This interphase absorbed solvent at a temperature below its glass transition and contributed to the resulting non‐Fickian time‐dependent diffusion process. The equilibrium diffusion coefficient was estimated to be 3.2 × 10−7 cm2/sec regardless of the casting surface. Nevertheless, according to the sorption measurements, the casting surface did have an effect on the approach to equilibrium. The results indicated a denser packing of the molecules and hence a decreased diffusion coefficient for Teflon and glass cast films, because of internal stresses left within the films during casting.
Plastic deformation of highly drawn polypropylene monofilaments
Authors: Garton A. , Carlsson D. J. , Sturgeon P. Z. , Wiles D. M.
Published: April 2003

The tensile properties of highly oriented polypropylene (PP) filaments are markedly dependent on their fabrication drawn history. Highly oriented filaments prepared by drawing at <100°C were capable of appreciable plastic deformation after passing through a marked yield point. This deformation process was very rate dependent, transforming to essentially brittle behavior at deformation rates >500%/min. Filaments produced by drawing at a higher temperature, or by annealing above 100°C of those produced at 100°C, had a slightly lower modulus, greatly reduced residual elongation to break, and showed no yield point. A model for the plastic deformation is proposed involving localized fibrillation to produce craze‐like structures. This model is consistent with the observed filament susceptibility to chromic acid etching. Electron micrographs of highly drawn then etched samples show that just prior to fracture only small plastes of the acid resistant (presumably original, unvoided) structure remain.
Dynamics of macromolecular chains. VI. Carbon 13 and proton nuclear magnetic relaxation of polystyrene in solution
Authors: Lauprêtre F. , Noël C. , Monnerie L.
Published: April 2003

Spin‐lattice 1H and 13C nuclear magnetic relaxation (NMR) times T1 have been measured for solutions of polystyrene in hexachlorobutadiene at two different frequencies. Some nuclear Overhauser enhancements and linewidths have also been determined. At 15 and 25 MHz the relaxation times T1 of the ortho and meta carbons show two different dependences on temperature. These measurements indicate internal motion of phenyl groups around the Cα—Cpara axis. A single isotropic correlation time is inadequate to explain the relaxation data for the para carbon. Use of a diamond‐lattice motional model reveals that segmental reorientation of the chain backbone of polystyrene can be described in terms of two correlation times, ρ characterizing the three‐bond motion process, and θ reflecting either isotropic motions of subchains or departure from an ideal lattice. Data on low‐molecular‐weight polystyrene indicate the participation of overall rotatory diffusion in the relaxation process. This motion is no longer efficient in high‐molecular‐weight polymers, where relaxation is due to segmental reorientation.
First‐order excluded‐volume effect on the intrinsic viscosity of nondraining polymer coils
Authors: Fujita H. , Taki N. , Norisuye T. , Sotobayashi H.
Published: April 2003

For a nondraining polymer coil in the vicinity of the theta temperature the cube of the viscosity expansion factor αη may be expanded in powers of the excluded‐volume parameter z as αη3 = 1 + C1z + C2z2 + ···. No exact values of the coefficients C1, C2, ···, are as yet known. This paper aims at evaluating C1 by the Kirkwood–Riseman formalism of polymer hydrodynamics with no mathematical approximation. The analysis gives C1 = 1.29, which is much smaller than 1.55 derived on the basis of the same formalism by Kurata and Yamakawa. The approximations used by these authors are discussed by comparison of their analysis with the present one. The first‐order excluded‐volume effect on the translational friction factor is also evaluated in the same way as for the intrinsic viscosity, and the result is shown to agree quite closely with the exact value determined by Stockmayer and Albrecht.
Dielectric properties of aromatic polyesters: Relaxation behavior of poly(diethylene glycol terephthalate)
Authors: Riande E.
Published: April 2003

The dielectric behavior of a low molecular weight fraction of poly(diethylene glycol terephthalate) has been studied over the frequency range 102 to 105 Hz for temperatures between −67 and +51°C. Two relaxations, α and β, which exhibit pseudoactivation energies of 52 and 8 kcal/mole, respectively, have been found. The α relaxation, associated with the glass transition of the polymer, is amenable to a Williams–Landel–Ferry (WLF) analysis. The dipole moment ration 〈μ2〉/Nm2 (where 〈μ2〉 is the mean square dipole moment of a chain consisting of N bonds and m2 is the average of the squares of the bond moments) has also been calculated using the dielectric data obtained for the polymer in the undiluted state. The calculations yield 〈μ2〉/Nm2 = 0.710, a value in very good agreement with that obtained from measurements in solution.
Birefringence of filled rubbers
Authors: Hashiyama M. , Stein R. S.
Published: April 2003

The birefringence change occuring upon stretching a rubber containing spherical isotropic filler particles is calculated as a function of the volume fraction of the filler. The stress concentration arising from the presence of the filler particles leads to an enhanced birefringence of the rubber. From a consideration of the detailed birefringence pattern about a spherical particle within a stretched rubber, the enhancement of the retardation is calculated as a function of the volume fraction of the filler particles.
Plane‐strain fracture energy instability and mixed mode crack propagation in polycarbonate at room temperature
Authors: Kambour R. P. , Holik A. S. , Miller S.
Published: April 2003

A study of crack propagation in double cantilever beam specimens of polycarbonate has revealed a large velocity‐dependent instability in the plane‐strain fracture energy GIc. At a crack velocity of 10−2 in./min, GIc accords with published values obtained from tensile studies of precracked specimens. Crack propagation in doubly grooved double cantilever beam specimens is unstable at higher velocities. The GIc's during crack jumping and at crack arrest are estimated to be 0.2 and 2%, respectively, of the low crack speed value, based on the amounts of crazing produced at the various crack speeds. Evidence of plane‐strain shear deformation at the low speed crack tip is presented. The GIc instability is suggested to arise from differences in the kinetics of shear failure and craze breakdown.
Intrinsic viscosity of polystyrene in mixed solvents
Authors: Munk Peter , Abijaoude Malek T. , Halbrook Michael E.
Published: April 2003

The intrinsic viscosity of a single sample of polystyrene was measured as a function of the composition of solvent in three mixed solvent pairs. The parameter Y introduced by Shultz and Flory was useful for prediction of trends, but severely overestimated the effect of solvent (1)–solvent (2) interaction on the expansion of polymer coils. The system polystyrene–cyclohexane–ethyl acetate was studied in detail for five samples of polystyrene. The analysis of the data provided strong experimental proof of a strict validity of the Mark–Houwink–Sakurada relation. The dependence of the Mark–Houwink–Sakurada exponent α on the composition of the solvent mixture was unexpectedly unsymmetrical. The unperturbed dimentions of the polystyrene chain are reduced by specific interaction of polystyrene with carbonyl groups in the solvent mixture.
On the location of chain‐ends in rapidly crystallized poly(ethylene terephthalate)
Authors: Aharoni Shaul M. , Harget Paul J.
Published: April 2003

Phenylmercurated poly(ethylene terephthalate) (PET) chain‐ends are obtainable through the transesterification of PET by phenylmercury hydroxide or acetate in solution in nitrobenzene at 165 ± 10°C. The reaction results in an average of one mercury atom per chain. The phenylmercuration may be followed by infrared or x‐ray fluorescence. Reaction with concentrated HCI Affords the elucidation of some structural parameters of the resultant partially crystalline tagged PET, through analyses of changes in viscosity and molecular weight, in percent crystallinity, and in the amount of mercury in the system. The chain‐ends are almost completely excluded from the stem region of the PET crystal with no more than 2% remaining. The chain‐ends are distributed unevenly throughout the amorphous phase. This is corroborated by sharp decreases in scattered intensity of small‐angle x‐ray measurements. Two models for the distribution of chain‐ends in the amorphous phase are considered. The one in which the ends are pushed farthest from the crystal surface and concentrate halfway between crystallites is tentatively adopted. Analysis of the HCI hydrolysis kinetics and products leads to the following picture concerning the fold tightness and position. About one out of five folds extends significantly into the amorphous matter where it is mingled with cilia, tie molecules, and unattached molecules. Random scission throughout such an amorphous mass should lead to a preponderance of cleaved molecules whose length should be four to five times the lenght of the crystalline stem region, as is indeed observed.
Theory of second‐order Raman scattering from a zigzag chain with application to polyethylene
Authors: Halley J. W. , Kleban P. H. , Onffroy J. R.
Published: April 2003

The extinction coefficient for acoustic branch, second‐order (two‐phonon) Raman scattering from a zigzag chain, using force constants and polarizabilities appropriate to polyethylene is computed. As a consequence of the computation, we propose identification of a line at 890 cm−1 in the published Raman spectrum of polyethylene as a second‐order Raman line.
Stability of heterocharges in poly(methyl methacrylate) thermoelectrets. II. Effect of γ‐irradiation on thermally stimulated current spectra
Authors: Vanderschueren J. , Linkens A.
Published: April 2003

Thermally stimulated currents (TSC) of γ‐irradiated poly(methyl methacrylate) thermoelectrets have been investigated in the high‐temperature range. The two main peaks of the TSC spectrum, appearing, respectively, at about 100 (α) and 120°C (ρ), show marked differences in stability under irradiation: while the α peak is little affected by doses up to 107 rad, the ρ peak vanishes following doses of 105 to 106 rad. On the other hand, a study of the rate of decrease of the ρ peak as a function of irradiation conditions reveals the important role of the surrounding atmosphere and the existence of a flux effect, probably related to irradiation‐accelerated diffusion of gas into the polymer. All these facts confirm the respective attributions of α and ρ peaks to a dipolar volume polarization and to an ionic space charge polarization, showing that the TSC study of irradiated thermoelectrets can be a useful method for identification of polarization processes in polymers.
Intramolecular excimer formation in macromolecules. I. Energy migration and excimer formation in copolymers exhibiting nearest‐neighbor excimer interactions
Authors: Reid R. F. , Soutar I.
Published: April 2003

Energy migration and intramolecular excimer formation have been studied in a series of copolymers comprising 1‐vinylnaphthalene, 2‐vinylnaphthalene, and styrene with methyl methacrylate. The technique of fluorescence depolarization was used to characterize energy migration in glassy solutions of the copolymers. The extent of energy migration in these copolymers is determined by the mean sequence length of aromatic species l̄a. Assuming that excimer formation occurs as a result of nearest‐neighbor interactions, the concentration of excimer sites in the macromolecule will be proportional to the fraction of links between aromatic species faa. It is proposed that these sites are populated via energy migration from the site of absorption. Proportionality between the ratio of excimer to monomer emission intensities and the function l̄a·faa was predicted. Good agreement with this relationship was obtained in each of the copolymer systems studied. Reactivity ratios of methyl methacrylate (rm) in copolymerization at 70°C with the aromatic monomers (ra) were determined as: 1‐vinylnaphthalene—rm = 0.43, ra = 1.71: 2‐vinylnaphthalene—rm = 0.37, ra = 4.46; styrene‐rm = 0.45, ra = 0.58.
Proton NMR study of molecular motion in polydimethylsiloxane
Authors: Burnett L. J. , Rottler C. L. , Laughon D. H.
Published: April 2003

Proton spin–lattice relaxation times T1 were measured for two samples of polydimethylsiloxane (PDMS), one with weight‐average molecular weight Mw = 77,400 and the other with Mw = 609,000. Two T1 minima and a T1 discontinuity were observed for each compound. The high‐temperature T1 minima were attributed to a stretching and flexing motion of the PDMS chain. Quantitative comparison of the relaxation data with a theoretical model developed for this motion allowed the activation energy, 2.3 kcal/mole, and the maximum angular displacement of the methyl group symmetry axis to be determined. The latter was found to be 31°, independent of sample molecular weight. The low‐temperature minima were ascribed to methyl reorientation with an activation energy of 1.6 kcal/mole. The T1 discontinuities were attributed to melting and allowed the degree of crystallinity to be estimated.
Mechanical properties of methanol crazes in poly(methyl methacrylate)
Authors: Kramer Edward J. , Krenz Heider G. , Ast Dieter G.
Published: April 2003

Methanol 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

The 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

A 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

The 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

Macromolecular 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

Kinetic 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

A 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

The 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

Diffusion 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

It 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

Ribbon‐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

In 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

Dielectric 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

The 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

Copolymers 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

First‐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

Proton 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

The 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

Results 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

The 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.
Molecular motions, the α relaxation, and chain transport in polyethylene crystals
Authors: Mansfield Marc , Boyd Richard H.
Published: April 2003

Conformational energy calculations are used to investigate molecular motions in polyethylene crystals. From these a model is derived for the motion that accomplishes the net rotation translation that is believed to underlie the nuclear magnetic resonance (NMR) and dielectric α processes in polyethylenes and paraffins (and their dipole decorated derivatives). The resulting model is found to incorporate features of a number of previous models but differs significantly from all of them. The rotation is accomplished by means of a twisted (by 180°) region that propagates smoothly along the chain across the crystal. It differs from previous rotational models in that the twisted region is found to be rather localized (to ∼12 CH2 units). A dependence of activation energy on chain length (paraffins) or crystal thickness (polyethylenes), with the activation energy becoming independent of thickness in thick crystals, results not from the rotational lattice mismatch of the twisted region per se but from the translational lattice mismatch induced by the 180° rotation of one stem relative to the other. The twist differs from a stable point‐defect twist previously proposed (Reneker defect) in that the chain torsion is relatively uniform through the twist and there is no shortening of the chain accompanying it. Further, the twist propagates smoothly without local barriers to its advance. Thus the propagating twist is to be through of as a transition state rather than a hopping defect. Detailed atomistic conformational energy calculations on C22H46 crystals were combined with a simplified elastic theory for translational stem mismatch in longer chains. From the combined calculations the activation parameters for twist propagation as a function of chain length or crystal thickness could be calculated. The results were compared with experiment for the dielectric α relaxation in paraffins containing dissolved ketones and polyethylenes containing carbonyl groups. The agreement is quite good, especially considering the paucity of adjustable parameters in the model. There is only some slight uncertainty in the calculated entropy of activation and a scattering correction was made a posteriori to account for a slow continued drop‐off in relaxation rate in very thick crystals.
Specific volume of polysulfone as a function of temperature and pressure
Authors: Zoller Paul
Published: April 2003

The pressure–volume–temperature (PVT) properties of a commercial polysulfone derived from bisphenol A and 4,4′‐dichlorodiphenylsulfone are studied experimentally and theoretically in the temperature range 30–370°C and for pressures to 2000 kg/cm2. PVT surfaces are determined for an annealed glass, formed under zero pressure, and for the melt. Two glass‐transition lines must be distinguished: T(P) which is the intersection of the glass and melt PVT surfaces, and Tg(P), which is obtained by pressurizing the melt isothermally. The application of Ehrenfest‐type equations to these transitions are discussed. The Prigogine–Defay ratio r = ΔkΔCp/TV(Δα)2 at P = 0 is found to be equal to 0.95 (±20%), using ΔCp data determined on identical samples. The melt data is compared with the Simha–Somcynski hole theory, using the reducing parameters V* = 0.788 cm3/g, T* = 12,560°K, P* = 10,875 bar. The hole fraction appearing in the theory is found to be constant along T(P), but the glass PVT relationship cannot be reproduced by using the Simha–Somcynsky theory together with the assumption that the hole fraction remains constant in the glass. At P = 0 the hole fraction must be allowed to decrease with decreasing temperature, but at a slower rate than in the melt.
The thermoelastic effect in glassy polymers
Authors: Gilmour I. W. , Trainor A. , Haward R. N.
Published: April 2003

The thermoelastic effect has been measured in compression on four glassy polymers; namely, polystyrene, poly(methyl methacrylate), polycarbonate, and epoxy resin. Quantitative results have been obtained for the first time on three of these polymers. It has been shown that by paying attention to specimen geometry and instrumentation results can be obtained to a high degree of accuracy (better than ±1.5% on a given set of measurements). The polymers are shown to obey the classical Thompson equation for thermoelasticity in solids over the temperature range studied (ca. 220–350°K). By inference such materials can be expected to behave classically in general. The results have been used, as first suggested by Trainor and Haward, to obtain values for the linear thermal expansion coefficient and the values so obtained are shown to be in excellent agreement, in general, with literature values obtained by more conventional methods. Results are given for a range of stress from 5 MN m−2 to between 25 and 50 MN m−2 according to ambient temperature. The method affords a measurement of parameters, in particular, linear thermal expansion coefficient. Values of specific heat for the four plastics have been measured by differential scanning calorimetry and the results compared with published data.
Calculation of the Grüneisen constant of glassy polymers from thermoelastic data
Authors: Gilmour I. , Trainor A. , Haward R. N.
Published: April 2003

Thermoelastic measurements on a glassy polymer make it possible to measure directly the quantity αV/Cp where α is the coefficient of linear expansion, V the specific volume, and Cp the specific heat at constant pressure. By further measuring the bulk modulus (BT) it is possible to derive a relatively accurate value of the thermodynamic Gruneisen constant (γT) where γT = 3BTαV/Cv. The values obtained decrease only slightly with temperature.
A differential scanning calorimeter study of the crystal forms and polymerization kinetics of 2,4‐hexadiynyl‐1,6‐bis(p‐toluenesulfonate)
Authors: Barrall Edward M. , Clarke T. C. , Gregges A. R.
Published: April 2003

The thermal properties of 2,4‐hexadiynyl‐1,6‐bis(p‐toluenesulfonate) have been explored by program temperature and isothermal differential calorimetry. The heat of fusion for the rapidly heated pure solid was 8254 cal/mole (34,540 J/mole) at 367.1°K (93.8°C). This amounts to an entropy change of 22.5 cal/mole °K (94.1 J/mole °K). The energy of activation for the thermal polymerizations was 18.97 kcal/mole (79.37 kJ/mole). The thermal polymerization appears to follow a solid–solid phase transition which proceeds by random homogeneous nucleation throughout the process. The kinetics were simple first order over 70% of the reaction. Programmed temperature studies indicate that during the first 10% of the polymerization a new high temperature (mp 375.4°K) solid phase is formed which acts as the monomer form during the bulk of the reaction.
Assessment of branching in polymers from small‐angle x‐ray scattering (SAXS)
Authors: Garg Sunil K. , Stivala S. S.
Published: April 2003

Small‐angle x‐ray scattering from solutions was applied in assessing branching using well‐characterized dextran hydrolyzates. It was found that the longitudinal and cross‐sectional properties of the polysaccharides vary in a manner predictable by the molecular topology of the chains. A hydrodynamically equivalent linear model for dextran is proposed and it has been shown that this model correctly predicts values of Φ and K, Flory's universal hydrodynamic constant and the Flory–Fox–Schaefgen parameter, respectively.