bluuebunny/crossref_metadata_2025_split huggingface dataset:
Solution grown isotactic polystyrene crystals. I. Degree and distribution of crystallinity; thermal stability
Authors: Overbergh N. , Girolamo M. , Keller A. 
Published: April 2003

AbstractThe subject of this paper is the degree of crystallinity and annealing behavior of solution grown single crystals of isotactic polystyrene (IPS) in relation to the fold length, an enquiry which acquires special significance in view of the fact that previously the fold length had been found to be identical over a wide range of crystallization temperatures (Tc). It was found that both crystallinity and thermal stability increase with Tc even over the range of constant fold length thus invalidating the usual assumption that the fold length and crystal properties are uniquely correlated. Further, the crystallinity figures as measured by conventional calorimetry are very low (<50% throughout) which by conventional ideas would require an unrealistically thick amorphous surface layer. However, the “linear crystallinity” (crystal core thickness as determined from x‐ray linewidths) is much larger, commensurate with crystallinities in single crystals from other materials. It is suggested that this is the more relevant figure for the subdivision of the lamellas into crystal core and surface layer. The additional amorphous content being otherwise accommodated. Further, this “linear crystallinity” is broadly unaffected by fold length changes induced by heat annealing. The thermal stability (including annealing ability) of the crystals differs markedly whether Tc is above or below ∼60°C, a Tc value which is in the range where the fold length is constant, but corresponds to a maximum in the crystallization rate. Possible connections between crystallization conditions and the stability of the resulting crystals (fold length considerations apart) are pointed out.
Melting of constrained drawn nylon 6 yarns
Authors: Todoki Minoru , Kawaguchi Tatsuro 
Published: April 2003

AbstractA differential scanning calorimeter (DSC) was used to study the melting behavior of drawn nylon 6 yarns which were prevented from shrinking during heating. The DSC curves exhibit a single melting peak at a higher temperature instead of the double peaks which, as reported previously, were observed in the unconstrained state. The curve is explained quantitatively in terms of the perfecting of the original crystals followed by monotonic melting of these crystals during heating. The single peak results from the absence of the partial melting–recrystallization process which plays an important role in the appearance of double peaks. The temperature of the melting peak for the constrained sample increases linearly with draw ratio, and is unaffected by drawing temperature and by annealing at constant length after drawing. The elevation of the melting temperature is discussed on the basis of the entropy effects predicted theoretically by Zachmann. Thermal analysis of constrained samples has proved to be useful for detecting oriented crystals which coexist with unoriented ones.
Fourier‐transform infrared study of polyethylene single crystals in suspension
Authors: Painter P. C. , Runt J. , Coleman M. M. , Harrison I. R. 
Published: April 2003

AbstractThe infrared spectra of polyethylene single crystals suspended in liquid are reported and compared to dried mats of the same material. In order to observe the polyethylene bands, liquids with partial windows in complementary regions of the spectra were chosen. Any remaining bands of the suspending media were removed by substraction of the spectrum of the pure liquid. The crystalline bands of suspended polyethylene are much sharper than those of the dried material, indicating a decrease in lateral crystalline order upon drying. Drying also results in a change in the type and distribution of conformations associated with amorphous and fold structures, as determined by the observed frequencies of the methylene wagging mode.
Oriented crystallization of biphenyl in low‐density polyethylene with a single texture
Authors: Dosière M. , Point J. J. 
Published: April 2003

AbstractDoubly oriented specimens with a single texture can be obtained by unidirectional rolling of a sheet of low‐density polyethylene. Swelling of the oriented samples with liquid biphenyl and in situ crystallization of the biphenyl give indirect information about the morphology of the polymer. In such samples, annealed a few degrees below the melting temperature, the orientation of the biphenyl crystals is a consequence of the interaction of the two crystalline lattices. The (001) biphenyl planes are parallel to the (h01) limiting planes of the lamellar polymer crystals. Theoretical considerations show that the epitaxial conditions are best fulfilled when the limiting planes of the lamellas are parallel to (201) planes. The experimental value of h is 3.
Stress birefringence in amorphous polymers under nonisothermal conditions
Authors: Matsumoto Takayoshi , Bogue Donald C. 
Published: April 2003

AbstractThe 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

AbstractThe 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

AbstractExtruded, 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

AbstractThe 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

AbstractEtching 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

AbstractIn 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

AbstractThe 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

AbstractSpin‐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

AbstractFor 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

AbstractThe 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

AbstractThe 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

AbstractA 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

AbstractThe 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

AbstractPhenylmercurated 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

AbstractThe 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

AbstractThermally 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

AbstractEnergy 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

AbstractProton 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.