bluuebunny/crossref_metadata_2025_split huggingface dataset:
A molecular approach to the spurt effect in polymer melt flow
Authors: McLeish T. C. B. , Ball R. C. 
Published: April 2003

AbstractThe Doi‐Edwards theory of polymer melts, extended to include relaxation processes associated with chain‐length equilibration, is used to make quantitative predictions of a discontinuity in the flow curve of a monodisperse melt in a capillary. A fluid interface between regions of high and low deformation rates is found to propagate from the former into the latter. Our results for the “spurt” and its hysteresis compare favorably with experiment using a molecular weight dependence of the ratio of “reptation time” (Td) to “equilibration time” (Teq) in agreement with that determined from nonlinear stress relaxation.
Viscometric behavior of liquid‐crystalline solutions of hydroxypropyl cellulose in N,N‐dimethylacetamide and in dimethylsulfoxide: Effects of temperature and concentration
Authors: Suto Shinichi , Obara Kazuhiro , Nishitani Suguru , Karasawa Mikio 
Published: April 2003

AbstractViscometric properties of two kinds of hydroxypropyl cellulose (HPC) solutions which exhibit liquid‐crystalline behavior under certain conditions were determined by using a cone–plate viscometer. Measurements included the temperature and concentration dependences of viscosity. A phenomenological superposition for the viscosity was also tried. The viscosity for the solutions of HPC both in N,N‐dimethylacetamide and in dimethylsulfoxide displayed a minimum and a maximum with respect to temperature and the specific viscosities at the minimum and the maximum decreased with increasing concentration. Concentration–temperature superposition for the viscosity of both systems could be applied over a limited concentration range. The physical interpretation is still obscure.
Evidence of two relaxation processes in the photon correlation spectra of poly(methyl methacrylate) above Tg
Authors: Fytas G. , Wang C. H. , Fischer E. W. , Mehler K. 
Published: April 2003

AbstractPhoton correlation functions of a high‐molecular‐weight PMMA (Mw = 1.06 × 107, Mn = 2.2 × 106, Tg = 103°C) have been studied in the temperature range 98 − 149°C. In contrast to previous results, two relaxation modes are observed in relaxation functions. The observed relaxation functions of PMMA are analyzed for the first time in terms of a continuous spectrum representing the distribution of retardation times. Using a modified computer program originally developed by Provencher, we have computed the spectrum of retardation times at various temperatures. The appearance of two distinct relaxation modes is clearly evident in the distribution of the retardation times and in the time correlation functions below 123°C.
Flow‐induced chain fracture of isolated linear macromolecules in solution
Authors: Odell J. A. , Keller A. 
Published: April 2003

AbstractThe recently developed elongational flow technique is applied to the examination of flow‐induced chain rupture of macromolecules in solution. For both closely monodisperse atactic polystyrene (a‐PS) and poly(ethylene oxide) (PEO), the critical strain rate for extension (\documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon _c $\end{document}) is found to depend upon molecular weight M as \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon _c \simeq M^{ - 1.5} $\end{document}, consistent with ideal Zimm dynamics. When the chains are subjected to strain rates beyond \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon _f $\end{document} the scission products correspond closely to one‐half of the initial molecular weight. The critical fracture stress depends upon molecular weight as \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon _f \simeq M^{ - 2} $\end{document}, enabling the prediction of the ultimate chain length which can be extended without fracture (\documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon _c = \dot \varepsilon _f $\end{document}). For a‐PS this corresponds to M = 3 × 107. These findings are well accounted for by Stokes' Law applied to an extended bead–rod model. The calculated flow‐induced force in the chain corresponds closely to the rupture force of a covalent backbone bond calculated from a modified Arrhenius rate equation. During the prefracture stage (\documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon _f > \dot \varepsilon > \dot \varepsilon _c $\end{document}) a‐PS shows anomalies in the flow‐induced birefringence, which suggest that the Phenyl side groups are becoming reoriented due to the progressive increase in free volume as the chemical backbone bonds stretch and the bond angles open.
Effects of loading conditions and temperature on environmental stress cracking of low‐density polyethylene
Authors: Ogata Nobuo , Yanagawa Teruaki , Yoshida Koukichi 
Published: April 2003

AbstractFracture mechanics was used to investigate the environmental stress cracking (ESC) of low density polyethylene (LDPE). Annealed and quenched samples were prepared; a single edge notch was made and the samples were fractured under constant load in a liquid methanol environment. The relation between the stress intensity factorKand the crack speed ȧ has been investigated. There is a large difference between annealed and quenched samples in the variation of this relation with temperature and applied load. The cause of this difference is discussed in detail. We propose that thermally activated molecular motion is essential to ESC of the annealed LDPE while stress concentration contributes markedly to ESC of the quenched LDPE.
The crystallization behavior of Cis‐polyisoprenes extracted from the guayule plant
Authors: Rensch G. J. , Phillips P. J. , Vatansever N. , Gonzalez V. A. 
Published: April 2003

AbstractThe crystallization kinetics and resultant morphologies of thin films of cis‐polyisoprenes from guayule rubber have been studied using osmium tetroxide staining and transmission electron microscopy. Polymers used were extracted from the plant either on a laboratory scale or in a pilot plant operation. The polymers show significantly different behavior with regard to both morphological features and to lamellar growth rates. Freshly extracted cis‐polyisoprene as well as freshly prepared specimens of pilot plant rubber show only α growth, as in cis‐polyisoprene from hevea, but a slightly faster lamellar growth rate. Aged pilot plant rubber shows both α and β growth, both at higher rates than in natsyn, with the rate of α growth being lower than in hevea. Freshly extracted and aged specimens show a maximum lamellar growth rate at −20°C, whereas the maximum for pilot plant rubber occurs at −24°C. The data are interpreted in terms of oxidation of double bonds during aging to produce pendant ester groups. Lamellar growth rates and infrared analyses are both consistent with 1.2–1.5% of the double bonds being affected. Data from guayule and natsyn are now consistent in showing that the effects of microstructural impurities on the crystallization of cis‐polyisoprene are to reduce the rates of α‐lamellar growth and to induce the β growth, which would not otherwise exist. Secondary nucleation analyses show the regime II–III transition, as in hevea; however, the temperature of the transition, as well as the ratio of the slopes, is different for this linear polymer.
Crystal morphology of the γ (triclinic) phase of isotactic polypropylene and its relation to the α phase
Authors: Lotz B. , Graff S. , Wittmann J. C. 
Published: April 2003

Abstractγ‐phase crystals of isotactic polypropylene (iPP) obtained from low‐molecular‐weight extracts of pyrolyzed polymers are examined by electron microscopy and electron diffraction. γ‐phase crystals differ from α‐phase crystals in three important respects: (i) they are elongated along the b* rather than the a* axis, (ii) the chain axis is inclined at 50° to the lamellar surface (indexed as 101) rather than normal to it, and (iii) they show screw dislocations, while α crystals do not. γ crystals are nucleated on the lateral (010) faces of a α crystals; the bα and b axes are parallel. Virtually no nucleation of the α phase takes place on the γ phase, which is therefore not involved in the repetitive lamellar branching leading to iPP quadrites. Crystallization of the γ phase appears to be favored by or linked to the absence of chain folds and may be involved in the macroscopic curvature of iPP branches.
Solubility of carbon dioxide, methane, and propane in silicone polymers: Effect of polymer side chains
Authors: Shah V. M. , Hardy B. J. , Stern S. A. 
Published: April 2003

AbstractThe solubility of methane, carbon dioxide, and propane in five silicone polymers was measured at 10.0, 35.0 and 55.0°C and at pressures up to 26 atm. The polymers were poly(dimethyl siloxane), poly(methyl propyl siloxane), poly(methyl octyl siloxane), poly(trifluoropropyl methyl siloxane), and poly(phenyl methyl siloxane). At a given temperature and pressure, the solubility of the penetrant gases decreases with increasing bulkiness of the polymer side chains, and with decreasing critical temperature of the penetrant. The solubility of carbon dioxide in poly(trifluoropropyl methyl siloxane) appears to be anomalously high, possibly because of specific penetrant/polymer interactions. The temperature and pressure dependence of the solubility coefficients for the penetrant/polymer systems studied are described, and different methods of correlating these coefficients are compared.
Dielectric relaxations in the liquid and glassy states of 47% polypropylene oxide in toluene as diluent
Authors: Johari G. P. , Monnerie L. 
Published: April 2003

AbstractMolecular relaxations in 47‐wt % polypropylene oxide of molecular weight 4000 in toluene as diluent have been studied by dielectric permittivity and loss measurements from 77 to 320 K, in the frequency range 1 Hz to 2 × 105 Hz. One relaxation process (β process) is observed in the glassy state below Tg (= 148 K), and two processes are observed in the supercooled liquid at T > Tg. Relative to the amplitude of the fast relaxation process (i.e., the local segmental motions of the polymer chain), the amplitude of the slow process is increased and that of the β process decreased on dilution of the pure polymer. The β process has an Arrhenius energy of 17 kJ mol−1. The rates of the two relaxations at T > Tg follow the Vogel–Fulcher–Tamman equation and seem to merge on cooling the liquid towards Tg. The relative temperatures at which the three relaxation processes occur at the rate of 1 kHz remain largely unaffected on dilution. The increase in static permittivity of the solution on cooling is more than anticipated from the temperature effects alone. It is suggested that the increase is due to the enhanced short‐range orientational correlation of the dipoles, which may involve H bonding.
Origins of endothermic peaks in differential scanning calorimetry
Authors: Alamo R. , Mandelkern L. 
Published: April 2003

AbstractThe origins of multiple peaks observed by differential scanning calorimetry have been examined in detail for a linear polyethylene fraction crystallized from dilute solution and for bulk‐crystallized copolymers of ethylene. At least two major bases are demonstrated. One is melting–recrystallization; the other a consequence of the distribution of crystallite sizes. The melting–recrystallization process, however, often only yields one endothermic peak. This peak is therefore not characteristic of the original crystallites present. In these situations complementary methods need to be used to determine the melting temperature. We have complemented the calorimetric studies with measurement of the crystallite size distribution as determined from the Raman low frequency acoustical mode spectra. A major increase occurs cooperatively in the crystallite size distribution during the initial melting. Most importantly, we have also been able to make a direct comparison between the interfacial free energies of thin crystallites formed from dilute solution and from bulk‐crystallized linear polyethylene.
Effects of thermal treatment of biaxially oriented poly(ethylene terephthalate)
Authors: Vallat M.‐F. , Plazek D. J. , Bhushan B. 
Published: April 2003

AbstractTwo distinguishable effects of thermal exposure of biaxially oriented poly(ethylene terephthalate) (PET) have been observed in the temperature range from room temperature to 140°C. Upon heating above the glass transition temperature Tg of the film an irreversible shrinkage of a few percent occurred with a concomitant decrease in the rate of creep. Some loss of orientation in the noncrystalline phase with an attendant slight increase in density is believed to be responsible. Since the film was anisotropic in its plane, different amounts and rates of shrinkage were observed along with differing thermal expansion coefficients in various directions relative to the primary optic axis. Upon cooling the 50% crystalline PET from above Tg to lower temperatures, reversible “physical aging” was observed. Creep rates were found to decrease with the residence time below Tg. As with purely amorphous polymers, the effects of the aging are removed by heating the specimen above Tg where the density of the amorphous phase achieves equilibrium values.
Crazing in thin films of styrene–butadiene–styrene block copolymers
Authors: Koltisko B. , Hiltner A. , Baer E. , Tung L. H. 
Published: April 2003

AbstractThe mechanism of craze initiation and growth and its relationship to mechanical properties has been studied in thin films of styrene–butadiene–styrene (SBS) block copolymers. Optical microscopy and transmission electron microscopy were used to examine three copolymers which has a spherical rubber domain morphology but varied in rubber content from 20 to 50%. With increasing rubber content, the crazes became longer and less numerous. Widening of the crazes was at least partially responsible for the higher strains achieved in the copolymers, especially for the composition with the highest rubber content where the crazes widened to form micronecks. Transmission electron microscopy revealed that craze initiation and growth at the craze tip occurred by cavitation in the polystyrene phase. Cavitation of the continuous phase rather than the rubber domains was attributed to the concentration of chain‐end flaws in the polystyrene. Crazes in the block copolymers followed a meandering pathway and the boundaries between crazed and uncrazed material were indistinct. Incorporation of fibrillated rubber particles into the craze fibrils strengthened the craze. At higher rubber content, the craze widened in the stress direction by voiding and fibrillation, which produced a cellular morphology.
Mechanical and dielectric relaxations of epoxide resins containing spiro‐ring structure
Authors: Ochi Mitsukazu , Shimbo Masaki , Saga Motoo , Takashima Naoichi 
Published: April 2003

AbstractLow‐temperature relaxation behavior was investigated for a bisphenol‐A and three spiroring type epoxide resins cured with aromatic and spiro‐ring‐type diamines. A new well‐defined relaxation denoted here as the β′ relaxation was observed from 50 to 100°C for the spiro‐ring‐type resin systems in both mechanical and dielectric measurements. The peak height and the activation energy of the β′ relaxation were entirely independent of the degree of curing. It is concluded that the β′ relaxation is due to the motion of p‐phenylene group adjacent to the spiro ring. The β′ relaxation was not observed in the bisphenol‐A‐type resin system.
Theoretical study of sequence distributions in polydienes. III. Kinetic treatment of first‐order Markovian process
Authors: Wang Zhiyu , Yan Deyue 
Published: April 2003

AbstractFor the first‐order Markovian process, a set of kinetic differential equations is listed which are adapted to the anionic polymerization of dienes. Using the method of non‐steady‐state kinetics, the probability functions for monads and dyads with various structures are rigorously derived on the merits of three different cases. As in the case of a Bernoullian process, the results obtained show that during the initial period of polymerization there is also an unsteady stage when the sequence structures in polydienes are dependent on reaction time t, monomer conversion Y, the initial molar ratio M0/I0 of monomer to initiator, and, therefore, the molecular weight of the products. The probability expressions are simplified to those obtained from a Bernoullian process if the ultimate unit effect can be neglected and those resulting from statistics when t, or Y, or M0/I0 is large enough.
Double‐step retraction of a polyisoprene vulcanizate: Comparison with molecular models
Authors: Thirion Pierre , Monnerie Lucien 
Published: April 2003

AbstractLarge stress peaks have been observed by subjecting a weakly crosslinked polyisoprene vulcanizate to double‐step extensions in opposite directions. The resulting retractions are well described by a BKZ constitutive equation with a strain‐dependent term identical to that for deviations from the statistical elasticity theory at equilibrium. This unexpected nonlinear behavior suggests that disengagement of pendant chains and attenuation of junction constraints both contribute to the stress relaxation of random networks.
Fast growth rates of polyethylene single crystals grown at high temperatures and their relevance to crystallization theories
Authors: Organ S. J. , Keller A. 
Published: April 2003

AbstractThe rates of growth of polyethylene single crystals grown from dilute solution in hexadecane and tetradecanol have been measured over the temperature range Tc = 98–120°C by following the change in turbidity during crystallization of a suspension of crystals of known shape and final size. The rates decrease similarly with Tc in each solvent, but for a given supercooling crystals grow much faster in tetradecanol where the corresponding crystallization temperature is higher. Similarly, the rates are much higher in hexadecane than those previously reported from xylene at equivalent supercoolings but lower Tc. Changes in the corresponding crystal morphologies as Tc is raised are quantified in terms of the axial ratio and the degree of curvature of the nominally {100} faces, both of which increase with Tc. The results can be interpreted as showing a transition from regime I to regime II growth in both solvents, which agrees both qualitatively and quantitatively with the predictions of the nucleation‐based kinetic theories. Such a transition has never before been reported for solution crystallization. Using this analysis, reasonable values are obtained for the crystal side‐surface energy σ of 7.4–7.5 erg cm−2 and for the regime I substrate length L of 0.14 μm. No correlation is found between crystal morphology and growth rate and there are no discontinuous changes in morphology at the proposed transition points. The occurrence of curved crystal edges raises the fundamental issue of how to reconcile noncrystallographic growth surfaces with nucleation‐controlled growth. A new approach to polymer crystal growth based on equilibrium surface roughening, which does not require nucleation, is therefore very pertinent in this respect and this is discussed.
Impingement mixing and its effect on the microstructure of RIM polyurethanes
Authors: Kolodziej P. , Yang W. P. , Macosko C. W. , Wellinghoff S. T. 
Published: April 2003

AbstractThe effect of impingement mixing on the microstructures developed during a reaction injection molding process in a thermoplastic urethane system was investigated. The polyurethane studied was a 4,4′‐diphenylmethane diisocyanate/l,4‐butane diol/poly(propyleneoxide) end‐capped with poly(ethy1eneoxide) polyol system with a 5/4/1 molar ratio. Three different impingement mixing levels ranging from Re = 80 to Re = 210 were implemented by a laboratory RIM machine. The samples were characterized by gel permeation chromatography (GPC), differential scanning calorimetry (DSC), optical microscopy, and transmission electron microscopy (TEM). Morphologies of hard‐segment globules, hard‐segment spherulites, and soft‐segment rich matrix were observed. The multiple DSC endotherms were related to different crystalline structures. A higher level of mixing was found to increase the molecular weight and produce more paracrystalline structures. A lower mixing level produced better phase separation and spherulitic structures. High temperature annealing caused transurethanization, which may allow molecular rearrangement and change the crystalline structures.
Analysis of trichroic infrared absorption in solids. III. Phase I poly(vinylidene fluride)
Authors: Fina L. J. , Koenig J. L. , Gordon W. L. 
Published: April 2003

AbstractTrichroic infrared absorption has been measured for oriented phase I poly(vinylidene fluoride). In addition to intensity differences, frequency shifts in the plane transverse to the draw direction are apparent. Shifts up to 10 cm−1 in one‐way drawn phase I are found for the CF2 stretching vibration (880 cm−1) between the direction normal to the film surface (thickness direction) and the remaining directions. Annealing the highly oriented films produces no major changes in the unique three‐dimensional structure. A model based on crystal defect structures is proposed to explain the unusual frequency shift behavior in the phase I PVDF. Possible conformations and a mechanism of formation of the defects are discussed.
Temperature dependence of unperturbed dimensions for stereoirregular 1,4‐polybutadiene and poly(α‐methylstyrene)
Authors: Mays Jimmy W. , Hadjichristidis Nikos , Graessley William W. , Fetters Lewis J. 
Published: April 2003

AbstractThe temperature coefficient of chain dimensions, d ln〈r2〉0/dT, was determined for stereoirregular 1,4‐polybutadiene and poly(α‐methylstyrene) via dilute solution viscometry. The 1,4‐polybutadiene was examined in oligomeric 1,4‐polybutadiene (an athermal solvent), and poly(α‐methylstyrene) was evaluated under near‐theta conditions using 1‐chloro‐n‐alkanes as solvents. Both approaches minimize the potential for influence by specific solvent effects. The resulting temperature coefficients, −0.10 × 10−3 deg−1 for 1,4‐polybutadiene and −0.30 × 10−3 deg−1 for poly(α‐methylstyrene) are in excellent agreement with rotational isomeric state calculations.
Thermodynamic study of poly(vinyl chloride)/polyester blends by inverse‐phase gas chromatography at 120°C
Authors: Riedl Bernard , Prud'Homme Robert E. 
Published: April 2003

AbstractPolymer/polymer interaction parameters χ′23 have been measured at 120°C as a function of polymer concentration for six different poly(vinyl chloride)/linear aliphatic polyester blends. The technique used is inverse‐phase gas chromatography with several molecular probes. The polymers investigated are poly(DL‐lactide), poly(ethylene succinate), poly(ethylene adipate), poly(butylene adipate), poly(δ‐valerolactone), poly(ε‐caprolactone) and poly(hexamethylene sebacate). Probe/polymer interaction parameters χ12 and polymer/polymer interaction parameters χ′23 values are dependent upon the methylene to carbonyl ratio of the polyester, reaching a minimum for a value of 5, this ratio corresponding to poly(ε‐caprolactone) blends. Results are interpreted in terms of pairwise interactions between carbonyl, methylene, and [CHCl] groups.