bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of thermal history, crystallinity, and solvent on the transitions and relaxations in poly(bisphenol‐A carbonate)
Authors: Varadarajan K. , Boyer Raymond F.
Published: April 2003

The following system of nomenclature for the transitions and relaxations in polycarbonate has been proposed: α = Tg = 150, β = 70, γ = −100, and δ = −220°C (frequency range of 10–50 Hz). The three component peaks of the γ relaxation are denoted by γ1, γ2, and γ3 relaxations correspond to phenylene, coupled phenylene‐carbonate, and carbonate motions, respectively. Dynamic mechanical analysis of poly(bisphenol‐A carbonate) using the DuPont 981–990 DMA system shows that the magnitude of the β relaxation depends upon the thermal history of the polycarbonate; annealing greatly reduces the intensity of the β relaxation. A relaxation map constructed for the β relaxation gives an activation energy of 46 kcal/mol. Exposure of polycarbonate to methylene chloride vapor for various times shows that after an induction period of about 5 min the intensity of the γ3 relaxation at −78°C decreases whereas the intensity of the γ1 relaxation of −30°C is unaffected and the ratio E″(γ1)/E″(γ3) increases linearly with the square root of time. This has been ascribed to the interaction of methylene chloride on the carbonate group in polycarbonate. Thermal crystallization of polycarbonate does not affect the positions of the γ relaxation and the glass transition peaks, but merely reduces their intensity. The glass transition peak intensity falls off sharply in comparison to the γ relaxation intensity. Both the γ3 and γ1 peaks in polycarbonate have been observed simultaneously for the first time by dynamic mechanical analysis. Impact strength measurements show that methylene chloride treatment of polycarbonate results in a change in mode of failure from ductile to brittle with a resultant 40‐fold reduction in impact energy for fracture. Thermally crystallized polycarbonate exhibits brittle fracture with very low force and energy at break.
Static and dynamic scattering behavior of regularly branched chains: A model of soft‐sphere microgels
Authors: Burchard Walther , Kajiwara Kanji , Nerger Dittmar
Published: April 2003

The static structure factor and the first cumulant of the time correlation function in dynamic light scattering have been calculated for a regularly branched molecule with n shells of branching generations which are connected by chains of m repeating units per chain. Ideal flexibility for the chains is assumed. The dynamic scattering functions of these soft spheres show behavior significantly different from that of a hard sphere. The theory describes very satisfactorily the static and dynamic light scattering results obtained experimentally with polyvinyl acetate microgels. The possibility of determining the glass transition temperature of latex particles is briefly discussed.
The influence of draw‐induced structural changes on the activity of a semicrystalline polymer‐supported catalyst
Authors: Cooper C. A. , Gates B. C. , McCullough R. L. , Seferis J. C.
Published: April 2003

The activity of a solid, polymer‐supported catalyst (a semicrystalline polyethylene film containing grafted, sulfonated styrene) was shown to be altered by cold drawing. The catalytic activity was measured by a test reaction, the dehydration of isopropyl alcohol to give propylene. Catalytic reaction rates were measured with variously drawn films clamped in a differential flow reactor operated at 100°C and 1 atm. The catalytic activity increased with the elongation of the polymer up to a draw ratio of 2.5; the activity decreased upon further drawing. The drawn films were characterized by x‐ray diffraction, dynamic mechanical measurements, electron microscopy, birefringence, and density measurements. Since no evidence was found for the formation of surface sites by creation of microcracks, the changes in activity are attributed to modifications in the polymer structure induced by drawing. The kinetics of the catalytic reaction and the data giving percentage crystallinity and crystalline and amorphous orientation factors suggest that, in the undrawn polymer, the catalytically active SO3H groups form a hydrogen‐bonded network, which is excluded from the crystalline regions. Initial elongation partially breaks up the network, allowing more SO3H groups to bond to alcohol and become catalytically engaged. Elongation beyond a draw ratio of 2.5 leads to a separation of SO3H groups greater than that required for the formation of the reaction intermediate, which involves the alcohol hydrogen bonded to several SO3H groups. The combined results of the catalytic kinetics experiments and structural characterizations imply that the preliminary deformation response of the semicrystalline polymer occurs predominantly within the noncrystalline regions and is accommodated by the rigid slip and tilting of crystal lamellae. The hydrogen bonding among the SO3H groups in the noncrystalline regions hinders lamellar breakup and suppresses the formation of highly aligned fibrillar morphologies.
Elastic modulus of crystalline regions of poly(butylene terephthalate) in the direction parallel to the chain axis
Authors: Nakamae Katsuhiko , Kameyama Masao , Yoshikawa Motoyoshi , Matsumoto Tsunetaka
Published: April 2003

The elastic modulus El of crystalline regions of poly(butylene terephthalate) in the direction parallel to the chain axis has been measured by the x‐ray diffraction method. Values of El for the (104) planes of the α‐ and β‐form crystal modifications were 13.5 X 104 and 21.0 X 104 kg/cm2, respectively. These values of El are very low compared with that of polyethylene terephthalate (110 X 104 kg/cm2). The results are discussed in terms of the molecular conformation in the crystalline regions.
Solution crystallization of nylon 12
Authors: Kyotani Mutsumasa
Published: April 2003

Electron microscopy and x‐ray diffraction data have been obtained on nylon 12 crystallized from 1‐hexanol, 1,6‐hexanediol, and hexylene glycol. Ribbonlike lamellar crystals of the γ form are obtained by crystallization from all the solutions and elongated flat crystals of the α form by crystallization from the 1‐hexanol and hexylene glycol solutions. The direction of the hydrogen bond in these crystals is almost parallel to that of maximum crystal elongation. α‐ and γ‐form crystals both grow from 1‐hexanol and hexylene glycol at appropriate crystallization temperatures. γ‐form crystals alone are obtained from 1,6‐hexanediol solution at every crystallization temperature. The long periods measured by small‐angle x‐ray diffraction for the solution‐grown crystals are in the range 7.6–10.6 nm. The melting behavior of the solution‐grown crystals is examined and discussed. The melting temperatures of the γ form may be lower than that of the α form. An equilibrium melting temperature of 208.4°C for γ‐form crystals is obtained by using a relation between thickness of lamellar crystals and their melting temperatures observed by differential scanning calorimeter measurements. Solvents affect the growth of the two crystalline forms in solution crystallization.
Glass transition temperatures of ABA poly(styrene‐b‐isoprene) block copolymers by differential scanning calorimetry
Authors: Meyer G. C. , Widmaier J. M.
Published: April 2003

The glass transition behavior of two sets of ABA poly(styrene‐b‐isoprene) block copolymers was examined by differential scanning calorimetry. In one series, the triblock copolymers had different total molecular weights and the same (30 wt %) polyisoprene content, in the other, the molecular weight was constant (30,000 g/mol) and the elastomer content was the variable. For all triblock copolymers studied, the data show an inward shift for the glass transition temperaturesTgof the corresponding homopolymers. This shift increases for the rigid‐phaseTgas the polystyrene block length decreases. Depending on their molecular characteristics, two, three, or only oneTgwere found. The thirdTgwas interpreted in terms of the existence of an interphase. Some of these conclusions could be confirmed by transmission electron microscopy.
Water mobility in a water‐soaked nafion® membrane: A high‐resolution neutron quasielastic study
Authors: Volino F. , Pineri M. , Dianoux A. J. , De Geyer A.
Published: April 2003

Water mobility in an acid Nafion® membrane containing ca. 15% water by weight has been studied by high‐resolution neutron quasielastic scattering (NQES). The data are analyzed in terms of simple models. On a scale of ca. 10 Å, the water molecules move practically as freely as in bulk water, but their long‐range motion is much more hindered. These results are important for an understanding of the relation between the microstructure and the macroscopic properties of these membranes. To our knowledge, this is the first detailed NQES study of the water‐polymer interaction problem.
The kinetics of defect clustering in fibrillar polypropylene crystals
Authors: Petermann J. , Gohil R. M. , Schultz J. M. , Hendricks R. W. , Lin J. S.
Published: April 2003

Polypropylene films were produced by solidification during high‐rate (>104s−1) melt drawing. Small‐angle x‐ray scattering (SAXS) data were collected during interruptions of the annealing of these films. Fibrillar crystallization took place during the melt‐drawing process. The fibrils exhibit an axial density modulation as determined by SAXS and transmission electron microscopy. Annealing increases the amplitude of the density modulation. Detailed examination of the SAXS curves shows that the modulation is approximately sinusoidal and that the amplification of the density modulation occurs with no change in periodicity. Comparison of SAXS curves taken at different times during annealing suggests a process similar to spinodal decomposition. It is proposed that the microstructural change within a fibril takes place by the axial motion and clustering of chain defects.
Stress relaxation of a polymer solution in double‐step shear deformations: A separate evaluation of the stress components due to entangled segments of different orientations
Authors: Osaki Kunihiro , Kurata Michio
Published: April 2003

When two shear deformations γ1 and γ2 are successively applied to an entangled polymeric system, a composite temporary network is formed. In this article a simple method is proposed for evaluating separately the contributions from the component networks of different deformations, γ1 + γ2 and γ2, to the observed shear and normal stresses. The method is applied to literature data for a polystyrene solution. It is revealed that the entangled chain segments formed between the applications of two deformations relax very rapidly, while those formed prior to the first deformation do not relax for quite a long time. The result is in accord with the conjecture based on the tube model of entanglement that the chain ends lose their orientation as the chain creeps out of an oriented tube.
The structure of an aminosilane coupling agent in aqueous solutions and partially cured solids
Authors: Ishida Hatsuo , Naviroj Somsak , Tripathy Sukant K. , Fitzgerald John J. , Koenig Jack L.
Published: April 2003

The molecular structures of partially cured polyaminopropylsilsesquioxane and aminopropyltriethoxysilane in water have been studied using Fourier‐transform infrared, laser Raman, and quasielastic laser light‐scattering spectroscopy. A multiply hydrogen‐bonded structure is proposed for the intramolecularly interacting amine and silanol groups on the basis of isotope exchange experiment and conformational energy calculations. Conformational restrictions are rather low for the proposed structure, which is thus suitable for the partially cured solid where there are slight perturbations by the surrounding amine and silanol groups. The O.…N distance was experimentally determined to be in the range 2.70–2.67 Å and estimated theoretically as 2.49–2.45 Å. The aminosilane in very dilute solution is found to be mostly monomeric. The isolated monomer‐oligomer transition lies around 0.15% by weight and this transition influences the amount of silane uptake by glass fibers. It is also proposed that this phenomenon may be general for surface treatments by silane coupling agents. Hydrolyzed aminosilane oligomers exist in part as submicron aggregates which can be broken up by the addition of an alcohol. The neutralized aminosilane hydrolyzes very slowly although it dissolves in water instantaneously. Micelle formation is also proposed.
Phase transitions in mesophase macromolecules. III. The transitions in poly(ethylene terephthalate‐co‐p‐oxybenzoate)
Authors: Meesiri Wiriya , Menczel Jozsef , Gaur U. , Wunderlich Bernhard
Published: April 2003

The glass and melting transitions of poly(ethylene terephthalate‐co‐p‐oxybenzoate)s have been studied by differential scanning calorimetry. Despite the higher glass transition expected for polyoxybenzoate, there is almost no change in the glass transition temperature up to 63 mol % oxybenzoate (353 ± 4 K). At high oxybenzoate concentration there seems to be a discontinuous jump to a glass transition of 450 K. This high glass transition has been observed in two‐phase materials down to 30 mol % oxybenzoate. The melting transition shows signs of isodimorphism with a minimum in melting temperature at about 60–70 mol % oxybenzoate, 60 K below the melting temperature of poly(ethylene terephthalate). The thermal properties are little affected by the change of the noncrystalline parts of the molecules to a mesophase structure. The transition to the isotropic phase could not be analyzed because of prior decomposition.
The characteristic ratios of stereoirregular polybutadiene and polyisoprene
Authors: Hadjichristidis Nikos , Zhongde Xu , Fetters L. J. , Roovers J.
Published: April 2003

The characteristic ratios of stereoirregular polybutadiene and polyisoprene have been evaluated by a combination of intrinsic viscosity and light‐scattering measurements under θ conditions. The polydienes were synthesized by anionic polymerization and thus had near‐monodisperse molecular weight distributions and were of uniform microstructure. The polybutadiene C∞ was found to be 5.1, which is in good agreement with the Abe–Flory predictions. However, the value of 5.1 for polyisoprene is somewhat higher than prediced by theory.
The heat of fusion of polytetrafluoroethylene
Authors: Starkweather Howard W. , Zoller Paul , Jones Glover A. , Vega Alexander J.
Published: April 2003

The heat of fusion of virgin and melt‐processed polytetrafluoroethylene (PTFE) was determined using the Clapeyron equation. Experimental data were obtained from PVT experiments and high‐temperature x‐ray diffraction measurements. For virgin, as‐polymerized PTFE, the melting temperature is given by

where, for Tm in degrees Celsius, A = 346.3±1.2, B = 0.095±0.003, and P is the pressure in kilograms per square centimeter. At the end of the atmospheric‐pressure melting interval, the amorphous and crystalline specific volumes V1 and Vc are 0.6517 and 0.492 cm3/g, respectively. Thus the heat of fusion is 24.4 cal/g, or nearly twice the value reported previously. The increases in enthalpy and volume at the melting point both indicate a degree of crystallinity of about 75–80% although infrared, x‐ray, and NMR data give much higher levels. Data from calorimetry, NMR, and dynamic mechanical measurements indicate that in virgin PTFE some of the crystals continue to experience torsional oscillations at temperatures below the room‐temperature transitions. This indicates that there are at least two kinds of crystalline regions. For previously melted PTFE, Tm is determined by A = 328.5±0.7 and B = 0.095±0.002, the volumes are Vam = 0.6349 and Vcr = 0.4855 cm3/g, and the heat of fusion is 22.2 cal/g. The entropy of fusion for PTFE is much closer to that of polyethylene than was previously believed.
Vapor‐liquid equilibria for polybutadiene and polyisoprene solutions
Authors: Saeki S. , Holste J. C. , Bonner D. C.
Published: April 2003

Vapor‐liquid equilibria in binary solutions of hydrocarbons (n‐hexane, benzene, toluene, cyclohexane) and chlorinated methanes [carbon tetrachloride (CCl4), chloroform (CHCl3), and dichloromethane (CH2Cl2)] in polybutadiene (PBD) and polyisoprene have been determined at 23.5°C by using the piezoelectric sorption method. The weight‐fraction activity coefficient of solvent (a1/w1) in cis‐PBD (98% cis‐1,4 addition) and random cis‐trans‐PBD (r‐PBD, 34.3% cis‐1,4 addition; 54.3% trans‐1,4 addition; 11.4% vinyl‐1,2 addition) are almost equal for CCI4, CHCI3, CH2CI2, benzene, and toluene solutions, while the values of a1/w1 in n‐hexane and cyclohexane solutions in cis‐PBD are larger than those in r‐PBD solutions. The values of a1/w1 for solutions of hydrocarbons and chlorinated methanes in cis‐1,4 polyisoprene (95% cis‐1,4 addition) have been compared with those for cis‐PBD.
Fluorescence probes for polymerization reactions: Bulk polymerization of styrene, n‐butyl methacrylate, ethyl methacrylate, and ethyl acrylate
Authors: Loutfy Rafik O.
Published: April 2003

Julolidine malononitrile 3 was used as a fluorescent probe for high‐conversion (free‐radical) bulk polymerization of methyl methacrylate, ethyl methacrylate, n‐butyl methacrylate, ethyl acrylate, styrene, and the copolymerization of styrene/n‐butyl methacrylate. The fluorescence of the probe increased gradually as polymer conversion increased. This was followed by an abrupt rise in fluorescence intensities by a factor of 3 to 40 depending on the polymer formed. Finally the fluorescence intensities leveled off as the polymer limiting conversion was reached. The polymerization region in which fluorescence intensity increases sharply seems to correspond to the increase of the rigidity of the medium at the glass transition. A correlation between the limiting quantum yield of fluorescence of the dye and the polymer glass transition Tg and expansion coefficient α was found. These results were interpreted in terms of rotation‐dependent nonradiative decay which links the excited‐state conformation to the rigidity of the medium.
Molecular aggregation of solid aromatic polymers. II. Mechanical properties of aromatic polyimide film
Authors: Isoda Satoru , Kochi Masakatsu , Kambe Hirotaro
Published: April 2003

Molecular aggregation of the aromatic polyimide poly(4,4′‐oxydiphenylene‐pyromellitimide) is influenced by the initial imidization temperature and by cold drawing. The effect of molecular aggregation in polyimides on their mechanical properties has been investigated. The density of a polyimide in which molecular aggregation gives an amorphous state is increased slightly by cold drawing. On the other hand, if molecular aggregation leads to a heterogeneous two‐phase structure, the density is decreased by cold drawing. With increasing initial imidization temperature, the α absorption peak in dynamic tensile measurements becomes broader and smaller, and shifts to a higher temperature. From analysis of correlations between molecular aggregation and mechanical properties, it is concluded that the mode of molecular motion corresponding to the α dispersion in polyimide is a long‐range cooperative motion of the main chain which is associated with the glass transition.
Statistical mechanics of aliphatic chain layers, influence of chain‐length mixing
Authors: Lemaire B. , Bothorel P.
Published: April 2003

A molecular model is used to simulate interfaces composed of surfactants and cosurfactants in microemulsions where molecules are anchored at the surface of spherical micelles. A Monte Carlo calculation of the conformational properties of the aliphatic layer is carried out taking into account the rotational isomerism of the chains and the binary random distribution of chain lengths. The thermodynamic behavior and the main structural features of the monolayer are analyzed in relation to some micellar properties.
The origin of polymer migration in a nonhomogeneous flow field
Authors: Sekhon G. , Armstrong R. C. , Jhon Myung S.
Published: April 2003

Flow‐induced polymer migration is treated in a rather intuitive though mathematically formal way. It is important to incorporate hydrodynamic interaction effects as well as flow geometry effects in studying polymer migration perpendicular to the flow direction. Simple examples, circular Couette flow in the free‐draining limit and plane Poiseuille flow in the nondraining limit, are chosen to illustrate the importance of such effects.
Three‐dimensional crystalline order in an atactic comblike polymer
Authors: Lupinacci Domenico , Winter W. T.
Published: April 2003

The production of oriented “crystalline” fibers of an atactic polymer, poly{1‐[6‐(4‐biphenylyloxy)hexyloxycarbonyl]ethylene} is reported. The x‐ray diffraction is consistent with a two‐chain unit cell with a = b = 23.5 Å, c = 6.48 Å, and γ = 120. Although the cell is essentially hexagonal, the absence of screw symmetry along the polymer chain reduces the crystal symmetry to P A packing model consistent with these data is proposed.
Investigation of molecular order in liquid‐crystalline solutions of cellulose triacetate using PMR spectroscopy
Authors: Patel D. L. , Gilbert R. D.
Published: April 2003

Liquid‐crystalline solutions of cellulose triacetate (CTA) in trifluoroacetic acid (TFA)–CH2Cl2, TFA–1.2‐dichloroethane (1,2‐DCE) solvent mixtures were examined by means of PMR spectroscopy. CTA forms both cholesteric and nematic phases in these solvents depending on the CTA concentration. In cholesteric solutions the CH2Cl2 signal is initially a singlet and then splits into a doublet. The time dependence of the splitting and the effect of CTA concentration are reported. The results suggest that the cholesteric phase slowly changes into a nematic phase in the magnetic field. The splitting of the CH2Cl2 proton signal into a doublet and the 1,2‐DCE signal into a quartet are due to direct magnetic dipole‐dipole interactions. Rotation of the sample in the magnetic field results in the disappearance of the doublet or quartet and suggests that the solvent molecules are originally oriented in the direction of the magnetic field. In the biphasic region, immediate splitting of the CH2Cl2 proton signal suggests that the anisotropic phase is nematic.
Effect of chain‐end free volume on the diffusion of oligomers
Authors: Von Meerwall E. , Grigsby J. , Tomich D. , Van Antwerp R.
Published: April 2003

We have used the pulsed‐gradient spin‐echo technique to measure self‐diffusion in low‐molecular‐weight polymers in the melt and dissolved in identical polymers of high molecular weight. Specimens used were cis‐polyisoprenes and polydimethylsiloxane. We find that, except for substantial free‐volume corrections, self‐diffusion in unentangled polyisoprene melts scales inversely with molecular weight. The results include sensitive determinations of chain‐end free volume.
Broad‐line NMR studies of molecular motion in cured epoxy resins
Authors: Banks L. , Ellis Bryan
Published: April 2003

The conformation of network chain segments in a rigid glassy DDM‐cured bisphenol A epoxy resin has been determined by means of rotational isomeric‐state model and confirmed by conformity of experimental NMR second moments with a theoretical estimate based on the model. The glass transition temperatures Tg have been determined from precipitate NMR line narrowing with increase in temperature due to the onset of rapid (>104 Hz) main‐chain molecular motion. The temperature dependence of the correlation frequency has been determined and the type and extent of molecular motion that occurs in such epoxy resins is discussed.
FTIR studies of calcium and sodium ionomers derived from an ethylene–methacrylic acid copolymer
Authors: Painter P. C. , Brozoski B. A. , Coleman M. M.
Published: April 2003

A systematic study of the sodium and calcium salts of an ethylene–methacrylic acid copolymer is reported. Fourier‐transform infrared spectroscopy (in the midinfrared region) is applied to the characterization of structural changes as a function of temperature and time of annealing. In the spectra of calcium ionomers, bands associated with carboxylate dimers are identified and assignments of specific spectral features to multiplets and clusters are discussed. The spectroscopic changes observed in the spectra of sodium ionomers differ somewhat from their calcium counterparts in that a single infrared band attributed to isolated carboxylate groups is observed. Assignments of specific bands to multiplets and clusters can, however, be made in a manner consistent with the interpretation of the spectra of calcium ionomers.
The entanglement network and craze micromechanics in glassy polymers
Authors: Donald Athene M. , Kramer Edward J. , Bubeck Robert A.
Published: April 2003

Crazes have been grown from crack tips in thin films of the following five polymers: polytertbutylstyrene (PTBS), polystyrene (PS), poly(styrene‐acrylonitrile) (PSAN), poly(phenylene oxide) (PPO), and poly(styrene‐methyl methacrylate) (PSMMA). These polymers represent a wide range of le values, where le is the chain contour length between entanglements. Quantitative transmission electron microscopy has been used to analyze the extension ratio λcraze and displacement profiles for these crazes. From these measurements the craze surface stresses have been computed by using the method of distributed dislocations. This analysis also permits an accurate measure of the level of the applied stress σ∞. These measurements show that the stress necessary for crazing increases as le decreases and that the higher surface stresses present at crack tips generate crazes that have higher λs than isolated crazes in the same polymers. Surface drawing is shown to be the dominant mechanism for craze thickening in all five polymers.
Mixed‐crystal infrared studies of chain folding in polyethylene single crystals: Effect of crystallization temperature
Authors: Jing Xiabin , Krimm S.
Published: April 2003

Mixed crystals of polyethylene (PEH) and various‐molecular‐weight perdeuterated polyethylenes (PEDs) have been prepared at 80°C and their infrared spectra compared with those of samples grown at 55°C. Concentrations of 80 PEH/1 PED were required in the former case to eliminate segregation effects whereas 40 PEH/1 PED sufficed in the latter. Resolution of the observed CD2 bend contour was most reasonably achieved with a crystalline singlet and two crystalline doublets, in addition to a contribution (ca. 15%) from the noncrystalline component. The singlet, comprising about 20% of the crystalline area, contains contributions from both isolated stems and (200) adjacent reentry folding. Random reentry folding is therefore not a predominant mode of chain organization in polyethylene single crystals. The inner of the two doublets arises from adjacent reentry folding along single (110) planes, and is present for all PED molecular weights. For low‐molecular‐weight fractions this splitting is consistent with the number of stems of one PED molecule allowed in the crystal. The outer doublet arises from multiple (110) plane adjacency, and is present for intermediate and high molecular weights. An analysis of both doublets suggests that at high molecular weights a single molecule can crystallize with noncontiguous regions of adjacent stem domains.
Theoretical birefringence of ultraoriented polyethylene from model structure calculations
Authors: Pietralla M. , Grossmann H.‐P. , Krüger J. K.
Published: April 2003

The birefringence of model structures of ultraoriented polyethylene has been calculated by using the point‐dipole concept and the polarizability tensor of the methylene group derived recently by Pietralla. For well‐oriented chains the birefringence is determined by the combination of a negative anisotropy of the polarizability tensor of the methylene group and a positive anisotropy of the Lorentz tensor, both with respect to the chain direction. As a consequence it decreases with increasing density. The results are in agreement with experimental values of Mead, Desper, and Porter. In the model the amorphous regions are regarded as a mixture of planar and helical segments arranged in nematiclike bundles which additionally may have a certain distribution of orientation. The birefringence is not much affected by defects which, on the other hand, strongly influence the ultimate mechanical properties.
Hydrodynamically induced formation of cellulose fibers. III. Coagulation of droplets of cellulose solution in extensional flow
Authors: Kalb B. , Cox R. G. , Manley R. St. John
Published: April 2003

The formation of cellulose fibers by coagulation of drops of cellulose solution in extensional flow was studied theoretically and experimentally. In the theory, which applies for slow‐motion conditions, homogeneity of the drop is assumed. The drop deforms according to a previously established deformation mechanism and becomes solid when a critical concentration of coagulant is reached at a certain position inside the drop. The theoretical predictions for the variation of fiber length with various parameters were tested experimentally in a four‐roller mill for cellulose/dimethyl sulfoxide/paraformaldehyde with glycerol as coagulant. In agreement with the theoretical predictions, it was found that fiber length increases with shear rate and original droplet size, but decreases with the diffusion coefficient of the coagulant in the cellulose solution.
Polyelectrolyte solutions: Counterion condensation and intermolecular interactions
Authors: Russel W. B.
Published: April 2003

This article demonstrates that the neglect of nonlinear effects in the conventional counterion condensation theory for the double layer about a charged cylinder can be significant, especially for phenomena involving intramolecular or intermolecular interactions in dilute solutions. For concentrated solutions the Manning theory derives from a linearized superposition approximation for the potential, in contrast to the cylindrical‐cell model, which explicitly treats interactions within an ordered array of parallel cylinders. A new theory which treats interactions explicitly while permitting disorder in two dimensions is presented, and predictions for the osmotic pressure are compared with those from the Manning and cylindrical‐cell models.
Compatibility of poly(ethylene oxide)–poly(vinyl acetate) blends
Authors: Kalfoglou Nikos K.
Published: April 2003

The compatibility of poly(ethylene oxide)–poly(vinyl acetate) (PEO‐PVA) blends was examined at five compositions covering the complete range. Samples were prepared by coprecipitation and solution casting. Dynamic mechanical properties were studied at 110 Hz between −120 and 65°C for dry, quenched, and annealed samples. The study also included tensile testing at 25°C, examination of blend morphology, and DSC measurements at elevated temperatures. Optical microscopy revealed that crystallization of PEO proceeds essentially unhindered at up to 25% poly(vinyl acetate) content by weight. Higher levels of this component drastically reduce spherulite size, and at the highest PVA compositions there was no evidence of crystallization. Thermomechanical spectra of quenched and annealed samples indicate limited mixing of the two components except for the higher (>75%) PVA compositions. Tensile properties show a mutual reinforcement at 10‐25% PVA content due to possible polymer segment association. The melting‐point depression of PEO is significant above 25% PVA and has been attributed to morphological changes of the PEO crystalline phase.
Thermodynamic properties of a polyelectrolyte solution containing a mixture of counterions of the same charge
Authors: Škerjanc J. , Dolar D.
Published: April 2003

Electrostatic internal and free energies are calculated for the cell model of a polyelectrolyte solution having two kinds of counterions of the same charge but different size. The calculation is based on the solution of the Poisson–Boltzmann equation obtained previously. The electrostatic contributions to the internal and free energies are presented as functions of valences, radii, and mole fractions of counterions, and their application to interpretation of experimental results is discussed.
Absolute integrated SAXS measurements during the crystallization of linear polyethylene
Authors: Lin J. S. , Hendricks R. W. , Schultz J. M. , McCready M. J.
Published: April 2003

Absolute intensity measurements of a dynamic small‐angle x‐ray scattering from a linear polyethylene were carried out during polymer crystallization from melt in a temperature range of 113.5° to 124.5°C. The mean‐square modulation of the electron density over the irradiated volume was evaluated and the feasibility of dynamic experimentation for crystallization kinetic analysis was established. The results provide an absolute value of mass density of the amorphous phase of a semicrystalline polymer at the crystallization temperature.
A study of the pressure‐volume‐temperature relationships of four related amorphous polymers: Polycarbonate, polyarylate, phenoxy, and polysulfone
Authors: Zoller Paul
Published: April 2003

The pressure‐volume‐temperature (PVT) relationships of bisphenol‐A polycarbonate, polyarylate, and phenoxy were studied at pressures to 1800 kg/cm2 and in both the glassy and melt states. Earlier data on polysulfone are included in the analysis and discussion of the results. All four polymers contain the bisphenol‐A residue in their repeat unit, together with a moiety of varying complexity, and are therefore somewhat related. At the glass transition, equations of the Ehrenfest type hold, provided the pressure dependence of the glass transition temperature is defined from the line obtained by intersecting the quasiequilibrium PVT relationship of the glass with the equilibrium PVT surface of the melt. The Prigogine‐Defay ratio r = ΔκΔCp/TgVg(Δα)2 at P = O is unity within experimental error for all four polymers. The melt data were fitted successfully to the Simha‐Somcynsky theory. Molecular parameters deduced from the reducing parameters vary in a reasonable manner among these four related polymers, lending support to the foundations of the theory.
Supermolecular structure of poly(ethylene oxide) fractions
Authors: Allen R. C. , Mandelkern L.
Published: April 2003

The crystalline morphology, or supermolecular structure, of poly(ethylene oxide) has been studied as a function of molecular weight and crystallization conditions. Molecular weight fractions, covering the range 6 × 103 to 1 × 107 are used over the range of accessible temperatures for isothermal crystallization as well as for a large set of controlled nonisothermal crystallization conditions. A morphological map is constructed from these studies and compared with the literature results. Prior reports were primarily confined to low molecular weights, which restricted the generalization of the findings. In the present work, as a consequence of the extended molecular weight range, conditions are established for the systematic development of several different, well‐defined, organized super‐molecular structures as well as for highly crystalline but disorganized systems. Strong similarities are found between the results for poly(ethylene oxide) and previous reports for linear polyethylene. A generalization for all chain molecules is suggested.
The effect of anhydrous ammonia on the crystalline‐state deformation of nylons 6 and 6,6
Authors: Kanamoto Tetsuo , Zachariades Anagnostis E. , Porter Roger S.
Published: April 2003

The aliphatic polyamides nylon 6 and 6,6 have been cold drawn by using the new concept of reversible plasticization with NH3. Two aspects were investigated: the effect of NH3 plasticization on the stress‐strain behavior of nylon 6,6, and the extent of NH3 absorption as determined by x‐ray analysis for the structurally simpler nylon 6. X‐ray analysis shows that ammonia is absorbed preferentially by the amorphous phase and that the plasticization has a significant effect on the unit‐cell orientation, the small‐angle void scattering, and the interplanar spacings between sheets of hydrogen‐bonded chains. The effect of plasticization was seen in the lower yield stress, the higher draw ratio (up to 8X) and tensile modulus (10 GPa) not attainable with unplasticized specimens.
Dynamical behavior of xanthan polysaccharide in solution
Authors: Jamieson A. M. , Southwick J. G. , Blackwell J.
Published: April 2003

Dilute‐solution hydrodynamic data for xanthan biopolymer in water suggest a rodlike molecule of dimensions 15,000 × 20 Å, and molecular weight 2.2 × 106 g/mol. Upon addition of NaCl to this system, the xanthan molecules self‐associate to form stable aggregates. The native xanthan conformation can be thermally denatured to a disordered coil which can be stabilized at room temperature in 4M urea. The transition to semidilute solutions is manifested by discrete changes in the concentration dependence of diffusion coefficient and zero‐shear viscosity at c ≈ 2.0 × 10−4 g/mL. At higher concentrations c ≥ 1.0 × 10−3 g/mL, the light‐scattering and shear‐viscosity data are qualitatively but not quantitatively consistent with predictions of the dynamical theory of Doi and Edwards for an isotropic entangled solution of rigid‐rod molecules. Measurements of latex sphere diffusion in xanthan‐water solution show a sudden retardation at c ≈ 1.0 × 10−3 g/mL, consistent with the cooperative formation of a motionally restricted network of long, thin, rigid fibers. At high shear rates, flow birefringence experiments indicate enhanced ordering of the xanthan chains in the semidilute regime.
Optical and calorimetric analysis of stress‐induced crystallization in natural rubber networks
Authors: De Candia F. , Romano G. , Russo R. , Vittoria V.
Published: April 2003

Stress‐induced crystallization of natural rubber networks is studied. The analysis is carried out using two different experimental techniques and the results are compared. In particular, the microcalorimetric and photoelastic results seem to be in disagreement, but the disagreement can be resolved by assuming that organization phenomena take place even at strains less than the critical value at which thermally detectable crystallization occurs. It is believed that such organization phenomena give rise to highly defective crystallites which behave as nucleation agents in the crystallization process that is induced at larger strains.
Some evidence against the existence of the liquid‐liquid transition. III. The evaluation of the Tll event by differential scanning calorimetry
Authors: Chen J. , Kow C. , Fetters L. J. , Plazek D. J.
Published: April 2003

The liquid‐liquid transition Tll has been examined by using differential scanning calorimetry as the tool of measurement. The results presented show that for the case of polystyrene, the Tll event appears to be an artifact caused by the presence of volatile components. Purified samples of polystyrene, polydienes, and poly(1‐butene) do not show the Tll transition.
Fractography of glassy networks formed from ethylene glycol dimethacrylate
Authors: Atsuta M. , Turner D. T.
Published: April 2003

Ethylene glycol dimethacrylate (EGDM) was polymerized to provide specimens suitable for three‐point bending tests. Fracture surfaces were generally similar to those reported previously for relatively brittle materials such as silicate glasses. Attention was concentrated on linear features which lay in roughly parallel arrays in the direction of crack propagation. Generally the features had a circular cross section which, in a few cases, tapered to a fine point. In other cases partially detached features were observed to have an irregular radius of curvature. The two preceding observations were interpreted as evidence of localized plastic deformation. The linear arrays of surface features were explained by adoption of Preston's mechanism for formation of “stries” in brittle materials. However, this mechanism calls for a characteristic cross section which in the case of poly(EGDM) was replaced by a circular cross section. To account for this difference, localized plastic deformation was invoked.
Studies of the effect of orientation on the elastic constants of stretched and hydrostatically extruded polychlorotriflouroethylene: A reorientational model in semicrystalline polymers
Authors: Cavanaugh D. B. , Wang C. H.
Published: April 2003

A reorientational model of polymer solids is given. The solid is described as a collection of small, orientable units. The elastic constants of the oriented polymer are given as a combination of the elastic constants of the orientable units and of the orientation parameters 〈P2(cosθ)〉 and 〈P4(cosθ)〉. The elastic constants of stretched and hydrostatically extruded samples of polychlorotriflouroethylene are obtained with Brillouin light scattering. These are fitted to the model and the orientation parameters are calculated. The elastic constants from the extruded samples are fit well by the model but the fit to the stretched film is less satisfactory. Hydrostatic extrusion in polymers is thus assumed to be a reorientation process in the amorphous phase, but the stretching process is not completely reorientational.
Entanglements and elasticity in polybutadiene networks
Authors: Brown D. R. , Munie G. C. , Jonas J.
Published: April 2003

Polybutadiene networks were prepared by peroxide crosslinking of monodisperse 1,4‐polybutadienes both in solution and in bulk. The effect of the entangled sol fraction on the elastic modulus of high‐molecular‐weight polybutadiene was observed in stress relaxation measurements. Sol fraction was shown to make a large contribution to the Mooney–Rivlin 2C2 term. This effect was also observed on the molecular level in NMR spin‐spin relaxation measurements. For networks crosslinked in bulk the stress relaxation measurements suggest the presence of trapped entanglements. The 2C2 term is insensitive to sol extraction in these networks. NMR spin‐lattice relaxation measurements in the rotating frame at 4.68 kHz verify the presence of additional effective crosslinks in these networks.
Crystallization of trans‐1,4‐polyisoprene
Authors: Anandakumaran K. , Kuo C. C. , Mukherji S. , Woodward A. E.
Published: April 2003

Crystals of fractionated trans‐1,4‐polyisoprene (TPI) were grown from amyl acetate solution at two weight fractions, 5.7 × 10−4 and 0.011; for the lower concentration a precooling followed by heating and then crystallization at temperatures in the 10–32°C range was used, while for the higher concentration this method and direct crystallization at a temperature TC in the 0–32°C range were employed. The precooling method yielded samples crystallized in the α form, while direct crystallization led to formation of β‐TPI at low TC and α at higher TC. The value for the DSC endotherm, characteristic of α‐form melting, increased with increasing TC, with a shift to lower values with increasing concentration for precooled samples. A β to α transformation was found to occur for synthetic unfractionated TPI when swollen with amyl acetate at 35°C for 17h. Swelling in n‐butyl acetate for one day at 25°C or 17 h at 35°C also led to this transformation. From experimental results 74°C is chosen as the temperature at which the α and β forms coexist in the bulk, and this is used to calculate the enthalpy of fusion of β‐TPI, yielding a value of 8.6 kJ mol−1.
The measurement of crystallite size in ultrahigh‐modulus polyethylene
Authors: Frye C. J. , Ward I. M. , Dobb M. G. , Johnson D. J.
Published: April 2003

Crystal length determinations have been undertaken on ultrahigh‐modulus linear polyethylene fibers by dark‐field electron microscopy. There is good agreement between the results and those obtained from wide‐angle x‐ray diffraction line broadening. The crystal length distributions from the dark‐field microscopy are also consistent with those determined by nitric acid etching. The significance of the present results is considered in the light of recent proposals for the structure of these materials and the achievement of high modulus.
Bimodal molecular weight distributions of a branched condensation polymer
Authors: Dubin P. L. , Kronstadt M.
Published: April 2003

Gel permeation chromatograms of a hindered‐phenolic, branched condensation polymer display pronounced bimodality at high conversion. The true molecular weight distributions, obtained by means of a GPC calibration curve based on narrow‐distribution fractions, exhibit corresponding anomalous high‐molecular‐weight “shoulders.” These results are discussed in terms of preferential aggregation and reaction of the higher‐molecular‐weight species during the polymerization, promoted by intermolecular hydrogen bonding in the apolar reaction medium.
Transient decay studies of photophysical processes in aromatic polymers. VI. Intramolecular excimer formation and dissociation in polystyrene and styrene–methyl methacrylate copolymers
Authors: Soutar I. , Phillips D. , Roberts A. J. , Rumbles G.
Published: April 2003

The time‐resolved fluorescence behavior of polystyrene and a series of styrene–methyl methacrylate copolymers has been examined by using pulsed laser excitation. Although the photophysical characteristics of styrene‐ and naphthalene‐containing polymers may be described by the same general kinetic scheme, some differences in the nature of the photophysical interactions are apparent. Umambiguous evidence for the occurrence of excimer dissociation into excited‐state monomer in polymers incorporating styrene chromophores is presented.
Self‐diffusion and sedimentation of dextran in concentrated solutions
Authors: Brown W. , Stilbs P. , Johnsen R. M.
Published: April 2003

Frictional coefficients for dextran in water have been evaluated from (i) self‐diffusion coefficients determined by pulsed‐field‐gradient NMR, and (ii) sedimentation coefficients in concentrated solutions. The results show that these frictional coefficients are only equal at infinite dilution and that fs increases more rapidly than fD* as the concentration increases.
Nonlinear rheological behavior of polymer systems for several shear‐flow histories
Authors: Menezes E. V. , Graessley W. W.
Published: April 2003

A stiffened and automated Weissenberg rheogoniometer has been used to measure time‐dependent nonlinear properties of several polymer solutions in simple shear flow. Departures from finite linear viscoelasticity are correlated with molecular structure. It is shown that certain features of behavior at high shear rates can be explained if the Doi–Edwards equilibration process is taken into account. A method is outlined for calculating the characteristic time τe for this process as a function of concentration, molecular weight, temperature, and branch length. This characteristic equilibration time is incorporated into a simplified BKZ constitutive equation. The proposed equation is found to adequately describe a wide range of experimental results both in step‐strain and continuous shear flows.
Rheology of a thermotropic polyester in the nematic and isotropic states
Authors: Wissbrun K. F. , Griffin A. C.
Published: April 2003

The rheological properties of a thermotropic polyester were determined in the nematic and isotropic states. In the isotropic state, the viscosity is almost constant and the polymer is only slightly elastic. The nematic phase has a lower viscosity than the isotropic, except at low frequencies or shear rates, where the viscosity increases as though the polymer had a yield stress. There is a marked dependence of the rheology on shear history. The effects of shearing can be erased by returning the material first to the isotropic state and then back to the nematic state. The results are discussed with reference to analogous observations in small‐molecule liquid crystals and in thermotropic aromatic co‐polyesters.