bluuebunny/crossref_metadata_2025_split huggingface dataset:
The heat of fusion of polytetrafluoroethylene
Authors: Starkweather Howard W. , Zoller Paul , Jones Glover A. , Vega Alexander J. 
Published: April 2003

AbstractThe 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

AbstractVapor‐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

AbstractJulolidine 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

AbstractMolecular 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

AbstractA 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

AbstractFlow‐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

AbstractThe 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

AbstractLiquid‐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

AbstractWe 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

AbstractThe 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

AbstractA 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

AbstractCrazes 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

AbstractMixed 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

AbstractThe 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

AbstractThe 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

AbstractThis 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

AbstractThe 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

AbstractElectrostatic 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

AbstractAbsolute 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

AbstractThe 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

AbstractThe 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

AbstractThe 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

AbstractDilute‐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.