bluuebunny/crossref_metadata_2025 huggingface dataset:
Solvent‐induced crystallization. II. Morphology
Authors: Durning C. J. , Rebenfeld L. , Russel W. B. , Weigmann H. D.
Published: April 2003

The Morphology of quenched poly(ethylene terephthalate) (PET) films crystallized by low‐molecular‐weight organic penetrants is studied by scanning electron microscopy. Films with thicknesses from ca. 1 mil (0.0025 cm) to ca. 35 mil (0.1 cm) were exposed to methylene chloride (MeCl2) andN,N‐dimethylformamide (DMF) in the temperature ranges 0–38°C and 22–70°C, respectively. The effects on the surface and internal structures of contact with liquids and saturated vapors were examined. Severe porosity at the surface results from contact with the liquids, but only minor surface roughness appears following contact with vapors. Internal porosity developed in the thinnest films (ca. 1 mil) during crystallization in liquid environments. Here, the internal void fraction is greatest along the film centerline and decreases with increasing crystallization temperature. A mathematical model discussed previously accounts for the observed behavior.
The heat of fusion of poly(4‐methyl pentene‐1)
Authors: Zoller Paul , Starkweather Howard W. , Jones Glover A.
Published: April 2003

We have combined pressure–volume–temperature measurements and high‐temperature x‐ray diffraction to calculate the heat of fusion of the poly(4‐methyl pentene‐1) crystal from the Clapeyron equation. We find ΔHf = 14.8 cal/g, only about half as large as several literature values. The new value of the heat of fusion leads to increased degrees of crystallinity, in agreement with the highly crystalline appearance of the x‐ray patterns of typical samples, in particular oriented fibers. The new entropy of fusion at constant pressure of 2.46 cal/deg per mole of monomer units is significantly lower than the values for polypropylene, polybutene‐1, and polypentene‐1, indicating possible ordering in the melt of this polymer.
Molecular orientation in biaxially oriented sheets of poly(ethylene terephthalate) II. Correlation of orientation averages with measured mechanical compliances
Authors: Bower D. I. , Jarvis D. A. , Lewis E. L. V. , Ward I. M.
Published: April 2003

The aggregate model is extended to examine the relationship between mechanical anisotropy and molecular orientation in one‐way drawn sheets of poly(ethylene terephthalate). It is assumed that both the aggregate and the unit of structure have orthorhombic symmetry. On the basis of a number of detailed assumptions regarding the appropriate application of the model, calculated bounds are obtained for the elastic constants that are in reasonable agreement with the experimental values. The implications of these results with regard to molecular orientation are considered, and it is concluded that both the chain orientation and orientation around the chain axis are important in determining the mechanical anisotropy.
The heat of fusion of polybutene‐1
Authors: Starkweather Jr. Howard W. , Jones Glover A.
Published: April 2003

Through x‐ray diffraction, the changes in the unit‐cell parameters of crystal forms I and II of polybutene‐1 were followed from room temperature to the melting point. These data were combined with the results of other measurements to computer the heats and entropies of fusion by use of the Clapeyron equation.
Gravimetric study of high‐pressure sorption of gases in polymers
Authors: Kamiya Yoshinori , Hirose Takuji , Mizoguchi Keishin , Naito Yasutoshi
Published: April 2003

A gravimetric method for determining precisely the solubility of gases in polymers at high pressure is described. The solubilities of N2 and CO2 in low‐density polyethylene (LDPE); CO2 in polycarbonate (PC); and N2, CH4, C2H6, and CO2 in polysulfone (PSUL) have been measured as a function of pressure up to 50 atm. Most of the measured sorption isotherms agreed closely with published data, but reproducible and time‐dependent hysteresis in the sorption of CO2, C2H6, and CH4 in glassy polymers, PC, and PSUL, was observed in this study for the first time. Like the well known conditioning effect of high‐pressure CO2 on the sorption capacity of glassy polymers, these hysteresis phenomena are believed to be due to the plasticizing effect of sorbed gases. On the basis of the current data, the dual‐mode sorption model including the plasticization by sorbed gas is discussed and a primitive equation for the concentration of sorbed gases in a quasiequilibrium state of sorption or desorption is proposed.
The molecular origin of lamellar branching in the α (monoclinic) form of isotactic polypropylene
Authors: Lotz B. , Wittmann J. C.
Published: April 2003

The specific lamellar branching characteristic of isotactic polypropylene (iPP) in its α monoclinic modification, first investigated in detail by Khoury, is analyzed in molecular terms on the basis of the geometrical and structural models of Padden and Keith and of Binsbergen and de Lange, respectively. As suggested by these authors the branching corresponds, structurally, to an homoepitaxy of the daughter lamellae on the lateral (010) faces of the parent lamellae; the epitaxy is favored by a satisfactory interdigitation of the molecular subgroups (methyl side chains) of facing planes and by the near identity of a and c parameters of the α monoclinic unit cell of iPP. On a molecular basis, the branching is initiated on a lateral (010) face made up of chains of a given hand by the deposition of chains of the same hand, whereas the crystal structure of the α modification would call for chains of opposite hand. Favorable interactions of side chains of helices of the same hand is realized only when the helix axes are at a substantial angle (in the present case, 100°) to one another. Related behavior is observed for the packing of α helices in the structure of globular proteins, in which molecular interactions, but no crystallographic interactions, are involved. On the basis of this molecular picture, the widespread occurrence of lamellar branching in the crystallization of the α form of isotactic polypropylene is accounted for, especially for high growth rates. At the same time, the specificity of the branching (only observed for the α crystal modification of this polymer) is explained by stringent geometrical and structural requirements that must be fulfilled at the contact plane.
Poly(p‐benzamide). II. Thermal behavior and crystal transformations
Authors: Takase M. , Ciferri A. , Krigbaum W. R. , Hacker H.
Published: April 2003

The thermal behavior and crystal transformation of poly(p‐benzamide) are reported. Modification I contains both solvent (N,N‐dimethylacetamide) and LiCl in its crystal lattice. Modification II is likely to form a complex crystal with LiCl, whereas crystalline modification III contains neither solvent nor LiCl in its unit cell. The crystal transformation temperature from modification I to II is 214°C, and the crystal–nematic transition temperatures of modification II and III are 475 and 544°C, respectively. Modification III can be obtained from II by heating above 475°C and cooling, or by washing with water. It can also be obtained from modification I by washing with water and annealing.
A molecular approach to the spurt effect in polymer melt flow
Authors: McLeish T. C. B. , Ball R. C.
Published: April 2003

The 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

Viscometric 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

Photon 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

The 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

Fracture 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

The 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

γ‐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

The 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

Molecular 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

The 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

Two 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

The 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

Low‐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

For 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

Large 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

The 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

The 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

Trichroic 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

The 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

Polymer/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.
Kinetics of fiber heat treatment. III Poly(butylene terephthalate) fibers
Authors: Peszkin Perla N. , Schultz J. M. , Lin J. S.
Published: April 2003

Small‐ and wide‐angle X‐ray scattering (SAXS and WAXS), shrinkage, and density experiments were performed on poly(butylene terephthalate) fibers which had been isothermally crystallized at different temperatures, and at constant tension, for times ranging from 100 to 1050 ms.

A consistent correlation among WAXS, SAXS, and the kinetic results is demonstrated. Shrinkage results show that the crystallization process prevails over the chain‐re‐coiling process. Density measurements show that the rate of crystallization increases with temperature. Pinhole X‐ray photos show that the orientation of the chains within the crystals remains constant with time and temperature. WAXS diffractometer scans show the development of wide‐angle Bragg peaks.

SAXS shows the development of small‐angle Bragg peaks, as the annealing time is increased. The two‐lobe arced pattern is the characteristic pattern. The value for long spacing ranged from 100 to 120 Å, increasing with temperature.
Response of the mean‐square optical anistropy of chain molecules to the imposition of excluded volume
Authors: Mattice Wayne L. , Saiz Enrique
Published: April 2003

The influence of the chain expansion produced by excluded volume on the mean‐square optical anisotropy has been studied in six types of polymers. The mean‐square optical anistropy for a specified configuration is calculated using the valence optical scheme. Realistic rotational isomeric state models are used for the configurational statistics of the unperturbed chains. Excluded volume is introduced by hard sphere interactions. Results obtained with chains of 100, 200, 300, and 400 bonds permit extrapolation to the behavior expected for much longer chains. The mean‐square optical anisotropy of polyethylene is insensitive to excluded volume. A similar conclusion was obtained several years ago in a study of chains confined to a tetrahedral lattice and weighted in a manner appropriate for the short‐range interactions in polyethylene.2 Different behavior is seen in poly(vinyl chloride), poly(vinyl bromide), polystyrene, poly(p‐chlorostyrene), and poly(p‐bromostyrene). The mean‐square optical anisotropy of these five vinyl polymers is sensitive to the imposition of excluded volume if the stereochemical composition is exclusively racemic. Much smaller effects are seen in meso chains and in chains with Bernoullian statistics and an equal probability for meso and racemic dyads.
Poly(chloropropylmethyl‐dimethylsiloxane)–polyurethane elastomers: Synthesis and properties of segmented copolymers and related zwitterionomers
Authors: Yu X. , Nagarajan M. R. , Li C. , Gibson P. E. , Cooper S. L.
Published: April 2003

A series of polyurethane block copolymers based on hydroxybutyl terminated poly(chloropropylmethyl‐dimethylsiloxane) and poly(tetramethylene oxide) soft segments of molecular weights 2100 and 2000, respectively, were synthesized. The hard segments consisted of 4,4′‐methylenediphenylene diisocyanate (MDI) that was chain extended with either 1,4‐butanediol (BD) or N‐methyldiethanolamine (MDEA). The materials chain extended with MDEA were ionized using 1,3‐propane sultone. The weight fraction of the hard segments was in the range 0.30–0.45. The effect of mixed soft segments, chain extenders, and zwitterionization on the extent of phase separation and physical properties was studied by utilizing differential scanning calorimetry and dynamic mechanical, stress‐strain, and Fourier Transform Infrared spectroscopy experiments. All of these short segment block copolymers showed nearly complete phase separation. The zwitterionomer materials exhibited ionic aggregation within the hard domains. Although hard segment crystallinity or ionic aggregation did not affect the morphology, hard domain cohesion was important in determining the tensile and viscoelastic properties of these elastomers.
The heat capacity of solid and liquid polystyrene, p‐substituted polystyrenes, and crosslinked polystyrenes
Authors: Judovits Lawrence H. , Bopp R. C. , Gaur U. , Wunderlich Bernhard
Published: April 2003

Heat capacities were measured for poly(4‐methylstyrene) [300–500K], poly(4‐fluorostyrene) [130–350K], poly(4‐chlorostyrene) [300–550K], poly(4‐bromostyrene) [300–550K], poly(4‐iodostyrene) [300–550K] and poly(styrene‐co‐divinylbenzene) with 1, 2, 4, 8, and 12 wt.% divinylbenzene (technical grade) [300–550K]. Polystyrene and poly(α‐methylstyrene) data were found to match the ATHAS data bank collections. Crosslinking causes no significant change in heat capacity, but substitution does. The heat capacities in the solid state are evaluated using approximate group and skeletal vibration spectra. Glass transitions are discussed, and full thermodynamic functions (Cp, H, S, G) can be calculated for amorphous, crystalline, and deuterated polystyrene as well as poly(α‐methylstyrene). Glassy polystyrene has an entropy of 7.5 J K−1 mol−1 at absolute zero. Changes of the heat capacity at the glass transition are explained and are predicted to go to zero for 50% poly(styrene‐co‐divinylbenzene) at about 550K.
Structure investigation of poly(p‐phenylene vinylene)
Authors: Granier Thierry , Thomas Edwin L. , Gagnon David R. , Karasz Frank E. , Lenz Robert W.
Published: April 2003

Electron diffraction patterns of highly oriented poly(p‐phenylene vinylene) films obtained by the soluble polymeric precursor route are interpreted on the basis of a monoclinic unit cell containing two monomer units: c (chain axis) = 0.658 nm, a = 0.790 nm, b = 0.605 nm, α ≃ 123°. The molecules are nearly perfectly oriented along the stretching direction but exhibit partial axial translational disorder.
Stress‐optical behavior of cycloaliphatic polyesters
Authors: Riande E. , Guzmán J.
Published: April 2003

Stress‐strain‐birefringence measurements were carried out on elastomeric networks of poly(oxymethylene‐1,4‐cis‐cyclohexylenemethyleneoxysebacoyl) at several temperatures between 5 and 80°C. The dependence of both the birefringence Δn and the true stress f/A on temperature was found to be linear for T > 30°C; for T < 30°C an anomalous increase in the birefringence and a sharp decrease in the stress was observed. This behavior suggests that crystallinity is developed in the strained networks at low temperatures, and the crystallites are oriented in the direction of the elongation. Values of the optical configuration parameter Δa ranged from 9.15 to 8.28 in units of 1024 cm3 in the temperature range studied. The value at 40°C of 1024Δa, obtained from experiments performed on swollen networks, amounted to 7.47 cm3. These results suggest that intermolecular interactions enhance the birefringence of the strained networks. The quantities Δa and d In Δa/dT were calculated by using the valence optical scheme. Although the calculations reproduce the temperature coefficient fairly well, the theoretical values of Δa are smaller than the experimental ones. The agreement between theory and experiment is better assuming that the CH2CH2COOCH2 segment is freely rotating.
The effect of plasticization on craze microstructure
Authors: Brown H. R. , Njoku N. G.
Published: April 2003

The structure of crazes in plasticized polystyrene has been studied by means of small‐angle x‐ray scattering and optical interference microscopy. Addition of plasticizer causes a rapid increase in the mean fibril diameter D and a slow decrease in the craze fibril volume fraction vf. The crazing stress σc was also measured and it was found that the product Dσc is independent of plasticizer concentration. These results are shown to be consistent with the entanglement model for controlling vf and the meniscus instability model of craze thickness growth.
The heat capacity of solid poly(p‐xylylene) and polystyrene
Authors: Kirkpatrick Donald E. , Judovits Lawrence , Wunderlich Bernhard
Published: April 2003

The constant‐pressure heat capacity Cp of poly(p‐xylylene) (PPX) has been measured from 220 to 625 K by differential scanning calorimetry. The constant‐volume heat capacities Cv of both, PPX and its isomer polystyrene (PS) have been interpreted in the light of literature data on full normal‐mode calculations for PS and estimates from low‐molecular‐weight analogs for PPX for the 39 group vibrations. Nine skeletal vibrations were used in this discussion with characteristic temperatures θ1 and θ3 of 534.5 and 43.1 K for PS. It was also possible to calculate a heat capacity contribution of a phenylene group within a polymer chain. Single 48‐vibration θ1 temperatures of 3230 K for PS and 2960 K for PPX are sufficient to describe Cv above 220 K. Below 140 K, PS heat capacity shows deviations from the Tarasov treatment.
The relationship between microstructure and mode of fracture in polyhydroxybutyrate
Authors: Barham P. J. , Keller A.
Published: April 2003

Polyhydroxybutyrate (PHB) is a bacterially produced thermoplastic. Melt‐cast PHB sheets are usually quite brittle. We show that this brittleness is due to cracks within the spherulites. These cracks, which may be either radial or circumferential within the spherulites, depending on the crystallization temperature, form under conditions of no externally applied stress. When the material is strained the cracks grow and join together, leading to brittle failure. It is possible to produce ductile PHB sheets in two ways: first, the cracks may be “healed” by a cold rolling process; second, special crystallization conditions can be used to produce ductile sheets consisting entirely of crack‐free spherulites. The relevance of this work to the ductility of crystalline thermoplastic in general is discussed.
Ultrahigh‐molecular‐weight polyethylene: Raman spectroscopic study of melt anisotropy
Authors: Wunder Stephanie L. , Merajver Sofia D.
Published: April 2003

The Raman spectrum of ultrahigh‐molecular‐weight polyethylene (UHMWPE) has been obtained in the temperature interval 135–208°C, a region where optical anisotropy was observed to exist. On the basis of our spectroscopic evidence, we believe that ordered regions persist in the melt above the calorimetrically determined melting point, and that part of the polyethylene chain is in an enviroment which is similar to that of the orthorhombic crystal. These ordered domains disappear with increasing temperature, but no calorimetric phase transition is associated with this change. We postulate that the very long relaxation times associated with the highly viscous melt keep the polyethylene chains in ordered environments which persist until decreased viscosity at increased temperature allows long‐range segmental motion. Our evidence supports the view that the melt anisotropy of UHMWPE arises from oriented slowly melting superheated crystals and not from a smectic liquid‐crystalline phase.
Determination of dual‐mode sorption and mobility parameters from permeation experiments
Authors: Toi K. , Oba K. , Maeda Y. , Ito T. , Shirakawa T. , Ikemoto I. , Tokuda T.
Published: April 2003

The precise pressure dependence of apparent diffusion and permeation coefficients was measured by using a microcomputer system for collecting and treating permeation data for CO2 in glassy poly(ethylene terephthalate) below 1 atm between 15 and 40°C. The partial immobilization model was used to determine the dual‐mode sorption and mobility parameters. The curves calculated with these parameters were in excellent agreement with experimental data. These parameters were also compared with sorption parameters obtained from measurements at 30°C. There was a small difference between the values of the parameters obtained from these permeation data and those from sorption data which we had previously obtained. Relations between this difference and the method of determination of the parameters are discussed.
Second and third virial coefficients for binary polystyrene mixtures in benzene
Authors: Sato Takahiro , Norisuye Takashi , Fujita Hiroshi
Published: April 2003

Light‐scattering second and third virial coefficients for benzene solutions (at 25°C) of two binary polystyrene mixtures, in which the molecular weight ratios of component fractions (essentially monodisperse) were 98 and 11.6, were determined as functions of polymer composition. The cross‐term virial coefficients A12 (for two different solutes 1 and 2), A112 (for two same solutes 1 and one solute 2), and A122 were evaluated from such functions. It was found that none of the existing theories for A12 yield a consistent and quantitative description of our experimental finding. No theory is yet available for A112 and A122, but the numerical values of these coefficients as estimated here are of interest in themselves.
Fundamental relationship between the nonequilibrium glassy state and yield stress of amorphous polymers
Authors: Chow T. S.
Published: April 2003

This paper reports the theoretical prediction and experimental verification of the connection between the yield stress of amorphous polymers and the physical aging phenomenon. The analysis reveals the existence of a fundamental relationship between the nonequilibrium glassy state and the thermally activated process controlling viscoelastic and plastic deformation. The results show that the volume relaxation and deformation kinetics share the same relaxation times, and that the activation energy for deformation below Tg is much smaller than previously mentioned in the literature. This indicates that the phenomenon of physical aging plays a very important role in the deformation and processing of polymers at low temperatures. The effect of quenching and annealing on the yield stress is described in terms of the mean energy of hole formation, the departure of volume from its equilibrium state, the distribution of hole energies, and lattice volume. The same set of molecular parameters obtained from the molecular kinetic theory of the glass transition and volume relaxation predicts the yield stress as a function of cooling rate, annealing time, temperature, and strain rate.
Films solidified from a lyotropic mesophase which retain the cholesteric structure
Authors: Watanabe Junji , Krigbaum W. R.
Published: April 2003

Solidified cholesteric films of α‐helical poly(γ‐methylL‐glutamate) and poly(γ‐benzylL‐glutamate) were prepared by casting from solutions of the lyotropic cholesteric mesophase. Colored films can be prepared in this manner, so the cholesteric structure is retained with a pitch corresponding to a visible wavelength. Their iridescent colors can cover the full range of the visible spectrum, and the colors remain unchanged for years. Although the films are similar in optical properties to those of fluid cholesteric phases, the temperature dependence of the color is quite different. On stretching, the film undergoes a permanent deformation, and the iridescent color is shifted toward the blue. Ift0is the initial film thickness and Δtis the change in thickness after stretching the film, the relative change in pitch, −ΔP/P0, of the cholesteric structure increases linearly with −Δt/t0in the range −Δt/t0> 0.10. This reduction of the pitch is attributed to a decrease in the number of pseudonematic layers in the span of one pitch, which may be interpreted in terms of delamination using an angle‐ply model of the cholesteric structure.
Elasticity of model poly(oxypropylene) networks
Authors: Andrady Anthony L. , Llorente Miguel A.
Published: April 2003

The equilibrium stress‐strain properties and the swelling behavior of moderately cross‐linked model networks of poly(oxypropylene) were studied. Results were in general agreement with the theory of rubber elasticity due to Flory. However, data on the highly cross‐linked networks (M̄c ≈ 725) could not be satisfactorily described by the recent theories of elasticity or swelling. This is believed to be primarily due to the marked non‐Gaussian character of the very short network chains and the substantial chemical modification of the polymer by the cross‐linking moiety which inevitably occurs at high cross‐link densities.
Morphologies and mechanical properties of pet films crystallized under high strain rates
Authors: Petermann J. , Rieck U.
Published: April 2003

The morphologies of highly oriented PET films, crystallized in a longitudinal flow gradient, were examined using transmission electron microscopy, differential thermal analysis, thermomechanical analysis, birefringence measurements, and mechanical tensile tests. The morphology in the as‐drawn state of the samples consists of oriented single micellar blocks which are embedded in the amorphous matrix. Annealing above 180°C causes a morphological transformation into lamellalike crystals, which are formed by lateral crystallization, preferably at the sidefaces of the micellar blocks. An interpretation of the mechanical behavior is given in accordance with the morphological model.
Dielectric properties of thermooxidized poly(vinyl formal)
Authors: Aoki Hiroyuki , Suzuki Tsutomu
Published: April 2003

An investigation was made of the correlation between changes in dielectric properties (110 Hz–4 MHz, 213–443 K) of poly(vinyl formal) and chemical structure during thermooxidation. As thermooxidation proceeds, the loss peak of the αa relaxation is displaced to higher temperature and cannot be detected in this temperature range. On the other hand, two loss peaks are observed in the region of the β relaxation and can be assigned to local motion of the main chain (βlocal) and end groups (βend). These two β relaxations are closely correlated with changes in chemical structure: the former is attributed to cleavage of the formal ring, formation of unsaturated bonds and cross‐linking; and the latter is assigned to aldehyde end groups. A good correlation exists between the total dielectric relaxation strength of the β relaxation and changes in carbonyl concentration. The carbonyl dipole moment is calculated as 2.68D by the Frölich‐Onsager equation. Thus, it is clear that carbonyl groups formed by thermooxidation have a strong influence on the dielectric properties.