bluuebunny/crossref_metadata_2025_split huggingface dataset:
Correlation of glass transition temperature and molecular weight: A model based on the principle of corresponding states
Authors: Dibenedetto A. T. , Dilandro L. 
Published: April 2003

AbstractThe molecular weight dependence of the glass transition temperatures of polystyrene, polyα‐methyl styrene, polyisopropylα‐methyl styrene, polymethylmethacrylate, polyvinylchloride, poly‐isobutylene, polyisoprene, and poly‐N‐octadecylmaleimide is described by an equation developed from the Principle of Corresponding States. A statistical analysis is used to test the adequacy of the equation, and it is shown that from a statistical point of view the three molecular parameters, Se/Sm, ε/ε, and Ce/Cm, characterizing, respectively, the ratios of contact area, lattice energy, and segmental mobility of end groups relative to repeating segments along the chain, will adequately describe the data. It is also shown that in one limit the equation reduces to the well‐known Ueberreiter‐Kanig result, which for most cases is a good first approximation to the data. The molecular weight‐TG data were used to estimate the depression of the glass transition temperature of polystyrene and polymethylmethacrylate by a series of plasticizers. It was concluded that in the absence of important changes in the molecular structure within a homologous series of polymers, the Principle of Corresponding States can be employed to describe the molecular weight dependence of glass transition temperature over the entire range of available data.
Epitaxial growth of long‐chain molecules on potassium hydrogen phthalate and potassium chloride substrates from the vapor phase
Authors: Zhang W. P. , Dorset D. L. 
Published: April 2003

AbstractPentacontane, hexacontane, 15‐ketohentriacontane (palmitone), and solid solutions of the two n‐paraffins were deposited from the vapor phase onto surfaces of potassium hydrogen phthalate (PHP) crystals and cleavage faces of potassium chloride (KCl) crystals in vacuo. Epitaxial growth, with molecular chains parallel to the substrates, occurs within a temperature range (e.g., 25–50°C for palmitone), and the epitaxial relationship between molecules and substrates was broken at higher temperatures. The electron diffraction patterns, similar to that of polyethylene, were obtained from all samples prepared at room temperature. The [100] or [130] directions of palmitone crystals are parallel to the substrate surface of PHP, and the [110] direction is parallel to that of KCl; the crystals in both cases are the orthorhombic form with lattice parameters a = 7.56 Å, b = 4.93 Å, c = 82.8 Å and a space group of Pna21. The (100) planes of n‐paraffin crystals are parallel to the surface of PHP, and the crystals are again orthorhombic. Also, solid solutions of n‐paraffins can be formed from the vapor phase, with the nucleation process on the two substrates being the same as for pure paraffins.
A dynamical study of the melting behavior of polypivalolactone single crystals by the X‐ray diffraction method
Authors: Kawaguchi Akiyoshi , Murakami Shozo , Kajiwara Kanji , Katayama Ken‐ichi , Nerger Dittmar 
Published: April 2003

AbstractWide‐angle and small‐angle X‐ray diffraction patterns of polypivalolactone single crystals were recorded as a function of temperature while heating at a constant rate. Long periods were found to increase abruptly at a certain temperature, while the degree of crystallinity decreased up to that temperature and then recovered on further heating, to an extent depending on the rate of heating. Multiple endotherms were observed in DSC measurements. The temperature at which the first endotherm peak was observed corresponded exactly to the temperature of the long period jump mentioned above. From these data, it is concluded that the original lamellar crystals melt at each peak temperature in the DSC thermogram and new lamellae are produced by subsequent crystallization. Multiple endotherms in the DSC thermogram are thus considered to represent repeated melt‐recrystallization processes.
Fiber formation from liquid‐crystalline precursors. II. Cellulose in N,N‐dimethylacetamide‐lithium chloride
Authors: Bianchi E. , Ciferri A. , Conio G. , Tealdi A. 
Published: April 2003

AbstractFibers were spun from isotropic and biphasic solutions of regenerated cellulose (DP = 290) in N, N‐dimethylacetamide +7.8% LiCl using water as a coagulant. There is an increase in mechanical properties through the isotropic → anisotropic transition with moduli reaching 22 GPa. The problem with this system is that crystallization encroaches on the biphasic region, and a pure mesophase is never observed. However, owing to the slow nucleation rate of the crystals, a biphasic solution is stable for a long time and can be spun to yield high modulus and orientation. The best approach is to use small flow gradients (extrusion rate and pick‐up ratio) and to allow long times for homogenization and nucleation of the mesophase.
Transport studies with model membrane
Authors: Siddiqi Fasih A. , Alvi Naved Iqbal 
Published: April 2003

AbstractThe most recent theory for salt concentration dependence of biionic potential, developed by Ikeda and his colleagues on the basis of thermodynamics of irreversible processes, has been compared with that of Nozaki et al. to get a relationship for the calculation of theoretical values of biionic potential. The latter are in good agreement with the experimental data gathered for the parchment‐supported manganese ferricyanide membrane in contact with various alkali chloride solutions.The conclusion of selectivity sequence of group Ia cations, reached on the basis of measurements of biionic potentials, is consistent not only with the findings of thermodynamic effective fixed charge density, evaluated by utilizing membrane potential equations provided by nonequilibrium thermodynamics, but also with the data on activation parameters calculated by making use of the theory of absolute reaction rates.The values of impedance Z, membrane resistance Rm, and membrane capacitance Cm have also been evaluated on the basis of a simple equivalent circuit model. Impedance values follow the theoretical predictions at high frequencies, but at lower frequencies there is a marked deviation from the ideal behavior probably due to roughness and nonhomogeneity of the membrane used in this investigation.
Plastic yielding of partially crystalline polymers
Authors: Gent A. N. , Madan S. 
Published: April 2003

AbstractMeasurements are described of characteristic stress‐strain properties in tension for several representative partially crystalline polymers prepared by cooling from the melt. Striking differences were found in the natural draw ratio, ranging from 2x to 11x. They are interpreted in terms of a simple molecular model of the yielding process in which polymer chains, folded to different degrees in the crystallites, are pulled taut. Values of yield and draw stress were found to be of the same order as the free energy Um of melting, suggesting that yielding and drawing take place by stress‐induced disruption of crystallites, analogous to melting. The mechanical work of drawing was similar to, but generally larger than, that required for melting, ranging from Um to about 4Um. The difference is attributed to strain energy of drawn material and possible recrystallization during drawing.
A procedure for predicting sorption equilibrium in ternary polymer systems from Flory–Huggins binary interaction parameters and the inversion point of preferential solvation
Authors: Campos Augustín , Gavara Rafael , Tejero Roberto , Gómez Clara , Celda Bernardo 
Published: April 2003

AbstractA procedure has been developed, based on the Flory–Huggins theory as generalized by Pouchlý, which permits the calculation of preferential (λ) and total (Y) sorption coefficients from previous information on the binary interaction parameters, χ, χ, and g12(ϕ10) and on the mixture composition at which the sign of λ inverts. The expressions obtained were applied to 10 cosolvent polymer systems for which experimental values of λ and Y are known. Practically in all the studied systems, the theoretical predictions are in fair accordance with the experimental data.
Polymerization of diethynyldiphenylmethane: DSC, FTIR, NMR, and dielectric characterization
Authors: Nguyen H. X. , Ishida H. , Hurwitz F. I. , Gorecki J. P. , D'Amore L. , Hyatt L. H. 
Published: April 2003

Abstract4,4′‐Diethynyldiphenylmethane thermally polymerizes by a free radical mechanism to a highly crosslinked structure of interest as a high temperature composite matrix resin. The polymerization reaction was characterized by differential scanning calorimetry, Fourier‐transform infrared (FTIR) spectroscopy, 1H and 13C nuclear magnetic resonance (NMR) spectroscopy, and microdi‐electrometry. The predominant reaction mechanism appears to be linear polymerization through the acetylene end groups, which follows first‐order kinetics. However, during the early stages of reaction a second, more rapid polymerization mechanism is evident; it is postulated that this is the formation of a cyclic trimer, which is kinetically favored but sterically prohibited as the crosslinked network grows. Formation of a liquid crystalline trimer is hyppthesized; such intermediate formation is supported by intensity increases in the aromatic region of the NMR spectra, by FTIR difference spectroscopy comparisons with model compounds, and by enhancement of conductivity as observed by microdielectrometry.
Solvent‐induced embrittlement in a crystallizable polyarylate
Authors: Berger Larry L. 
Published: April 2003

AbstractThe effects of solvent‐induced crystallization on the micromechanical properties of thin films of polyarylate (PAr) were studied. Under uniaxial extension amorphous polyarylate was observed to deform exclusively by shear deformation with no evidence of crazing. Upon exposure to methylethyl ketone, vapor, or liquid, PAr crystallizes and is subsequently embrittled. Our transmission electron microscopy results clearly show that this embrittlement results from a transition in plastic deformation mechanism from shear yielding to crazing. A detailed examination of the samples revealed that the crazes formed preferentially within the noncrystalline regions and that the craze tips followed a complex trajectory around the crystallites. In some cases the craze tip advance deviated by as much as ±30 from a direction normal to the tensile axis. Because crazes are inherently more susceptible to forming cracks than shear deformation zones, crystallization reduces the fracture toughness of the polymer. This type of embrittlement, via a transition in plastic deformation mechanism, is believed to be a general behavior for solvent‐crystallizable thermoplastics.
Development of supermolecular structure in polystyrene latexes
Authors: Yang Se‐in , Klein A. , Sperling L. H. 
Published: April 2003

AbstractThe development of supermolecular structure in polystyrene latex particles was investigated by small‐angle neutron scattering (SANS). Seed latexes of deuterated polystyrene were swollen with an equal mole‐% of protonated styrene monomer, equilibrated, and polymerized to complete conversion. The scattering patterns reflect the extent of supermolecular structure development inside the particle. The data were analyzed by separating the Debye single‐chain and spherical scattering form factors. The extent of segregation was found to depend on the relative size of the chains compared with that of the particle, going through a maximum at the ratio Mw/D of about 0.1, where Dw represents the weight‐average diameter of the latex particle. When the chain dimensions are relatively very small, uniform molecular mixing is obtained. The best model for the segregated system is a graduated core‐shell supermolecular structure.
On the Pace–Datyner theory of diffusion of small molecules through polymers
Authors: Kloczkowski A. , Mark J. E. 
Published: April 2003

AbstractThe Pace–Datyner theory for diffusion of penetrant molecules in polymers has been analyzed. It has been found that the correct solution of the problem they pose is possible only at 0 K, since then the separation of two chains at x = ∞ is equal to the minimum of the DiBenedetto potential for their interaction. Otherwise the energy of symmetrical separation is infinite. By using the linearization method to solve the differential equation, Pace and Datyner neglected the problem of unnatural boundary conditions at x = ∞ for temperatures above 0 K. The exact numerical solutions of differential equations at temperature 0 K were therefore compared with the results of the Pace–Datyner linear approximation. For temperatures different from 0 K the solution of the problem is possible only when the proper cutoff is imposed. The analytical expression for the coeffients in the DiBenedetto potential has been found, and the potential can be written as
Growth and decay of concentration fluctuations in polymer–polymer mixtures
Authors: Ohnaga Takashi , Inoue Takashi 
Published: April 2003

AbstractA computer simulation based on the Cahn–Hilliard nonlinear diffusion equation, developed in the field of metallurgy, is applied to the demixing behavior of a polymer–polymer mixture. The simulation is a one‐dimensional version. Spatially periodic concentration fluctuations appear at a very early stage and evolve with the wave number almost constant. Later some waves are absorbed into neighboring ones, resulting in a decrease in the average wave number of the concentration fluctuation. Thus, characteristic phenomena in the demixing are successfully described by the computer simulation. Furthermore, the simulated time variation of wave number agrees with experimental results in the literature. The analysis is extended to two‐step quenching: after a homogeneous mixture undergoes the first temperature‐jump from the single‐phase region to the two‐phase region of the phase diagram, the system is allowed to demix isothermally for a time, and then the demixed system undergoes the second jump to deeper or shallower quench. When the quench depth of the second jump (ΔT2) is smaller than half the first depth (ΔT1), the concentration fluctuation as developed under ΔT1 decays with time after the second jump. When ΔT2 is between ΔT1 and (ΔT1/2), the fluctuation decays slightly after the second jump and then increases. When the second jump is to a deeper quench (ΔT2 > ΔT1), a new fluctuation of short wavelength is superimposed on the previously developed one.
Sharp fronts due to diffusion and stress at the glass transition in polymers
Authors: Cohen Donald S. , White Andrew B. 
Published: April 2003

AbstractWe derive and analyze a model for sharp fronts in glassy polymers. We take the major effect of a diffusing penetrant on the polymer entanglement network to be the inducement of a differential viscoelastic stress. This couples diffusive and mechanical processes through a viscoelastic response where the strain depends upon the amount of penetrant present. Analytically, the major effect is to produce explicit delay terms, via a relaxation parameter, to account for the fundamental difference between a polymer in its rubbery state and the polymer in its glassy state, namely the finite relaxation time in the glassy state owing to slow response to changing conditions. We produce concentration profiles in good agreement with observations on sharp front formation. In addition the model can account for the phenomenon of sorption overshoot.
Transitions and morphology of a thermotropic liquid‐crystalline polyester with a flexible spacer
Authors: Hu Shiru , Xu Mao , Li Jianchang , Qian Baogong , Tao Kung , Lenz Robert W. 
Published: April 2003

AbstractThe mesomorphic transitions, crystallization from the mesophase, and the influence of the specimen preparation method on the solid‐state structure of an aromatic polyester containing a triad aromatic ester mesogenic group and a decamethylene flexible spacer in the main chain were studied by DSC, SALS, WAXS, polarizing microscopy, torsional braid analysis, and depolarizing transmittance techniques. The specimens obtained from solution were semicrystalline and exhibited nematic mesophase formation above the melting point Tm, whereas the melt‐cast specimens were mesomorphic as cast. A transition from the nematic phase to another mesophase, designated Mx, is proposed to occur below Tm, so this transition is monotropic. It appears that the transition to the Mx mesophase occurs before, and may even be a prerequisite for, crystallization of the melt‐cast specimens. The thermal expansion coefficient of the anisotropic melt is close to that of the isotropic melt, and the Tg of the supercooled solid mesophase is close to that of the amorphous phase.
Poly(ethylene oxide)/poly(ethyl methacrylate) blends: Crystallization, melting behavior, and miscibility
Authors: Cimmino Sossio , Martuscelli Ezio , Silvestre Clara , Canetti Maurizio , De Lalla Claudia , Seves Alberto 
Published: April 2003

AbstractResults of an investigation of isothermal crystallization and thermal behavior of poly(ethylene oxide)/poly(ethyl methacrylate) (PEO/PEMA) blends are reported. The blend composition and the crystallization temperature strongly influence the crystallization process from the melt and the melting temperature of PEO. The addition of PEMA to PEO causes a depression in the spherulite growth rate, in the overall kinetic crystallization constant, and in the melting temperature. Experimental data on the radial growth rate G and overall kinetic rate constant Kn are analyzed by means of the latest kinetic theory. From this analysis it emerges that the crystallization of pure PEO and PEO in the blend conforms to the regime I process of surface secondary nucleation. The depression of the melting temperature cannot be explained only in terms of a diluent effect due to the compatibility of the two components in the melt. Annealing and morphological effects, dependent on composition and time, must also be taken into account.
A nonequilibrium thermodynamic description of dilute polymer solutions
Authors: Pérez‐García C. , Casas‐Vázquez J. , Lebon G. 
Published: April 2003

AbstractThe purpose of this paper is to justify the well‐known relaxation spectra observed in dilute polymer solutions from extended irreversible thermodynamics. This is performed by elevating the viscous stress tensor to the status of independent variable, in addition to the usual variables, like temperature and mass density. In particular, it is shown that our thermodynamic description encompasses the Rouse and Zimm models. Memory functions for the longitudinal and transverse correlation functions are derived and analyzed within the frame work of molecular hydrodynamics.
Investigations of comblike polysiloxanes. I. The influence of spacer length on dielectric relaxation studies of aligned samples
Authors: Simon R. , Coles H. J. 
Published: April 2003

AbstractDielectric relaxation studies on aligned liquid‐crystalline comblike polysiloxanes are presented. The polymers differ only in the length of the flexible spacer separating the mesogenic side groups from the polysiloxane backbone. The characteristic features of the observed relaxation process as a function of frequency and temperature, in both the liquid‐crystalline and isotropic phases, are described, and the effect of the spacer length is discussed. Within the liquid‐crystalline phase a narrow single loss process is observed, due to the relaxation of the mesogenic side groups around the polymer backbone, whereas in the isotropic phase a much broader loss curve is seen. The transition from an aligned polymer mesophase to the randomly aligned isotropic phase is also studied in detial, and comparison with earlier work on comblike polyacrylate and methacrylate liquid crystals is presented.
Fiber spinning from the nematic melt. VI. Flow instabilities in the 30:70 copolyester of hydroxybenzoic acid and 2‐hydroxy‐6‐naphthoic acid
Authors: Yang D.‐K. , Krigbaum W. R. 
Published: April 2003

AbstractThe rheological behavior and fiber spinning are investigated for the Celanese liquid crystal copolyester 30 mol% p‐hydroxybenzoic acid and 70 mol% 2‐hydroxy‐6‐naphthoic acid (designated as 30HBA/70HNA) with inherent viscosity 7.8 dL/g. Shear thinning viscosity, and yield stress are observed at low shear stress, which probably results from the existence of crystallites in the melt.The crystal‐nematic melting point of the copolymer, as measured by differential scanning calorimetry, is around 309°C. Extrudates are collected at four different temperatures ranging from 315 to 345°C. Melt fracture and die swell are observed above 335°C at low shear stress. A wide‐angle x‐ray diffraction (WAXS) study of an annealed sample indicates that the abnormal phenomenon may be due to crystallites arising from blocky units of HNA. Fiber spinning is performed at high shear rate at 325 and 335°C. Flow is stable under these conditions. The spin draw ratio is the ratio of take‐up velocity to the velocity of extrudate existing from the capillary. The initial modulus reaches a maximum at a fairly low spin draw ratio. Instron and wide‐angle x‐ray (WAXS) studies show that the mechanical properties and orientation are poor for the fiber spun near the crystal‐nematic melting point. Also, thermal history is found to affect the rheological behavior. Heat treatment offibers, particularly those which are well oriented, brings an improvement of mechanical properties.
Texture development in polyethylene. I. Uniaxial extension and uniaxial compression
Authors: Krause Stephen J. , Hosford W. F. 
Published: April 2003

AbstractTexture development of high‐density polyethylene has been studied by x‐ray diffraction at various strains for uniaxial extension, as achieved by uniaxial tension and extrusion, and for uniaxial compression. Pole distributions were measured for the (100), (200), (020), and (011) reflections. Textures were described by ideal single‐crystal orientations with inverse pole figures. In uniaxial extension, samples were deformed up to true strains of 1.83 (reductions of up to 84%). After a strain of 0.55, the c axis oriented at 35° from the extension axis and with increasing strain approached the extension axis. This was attributed to initial (110) or (310) twinning in combination with (100) slip, followed subsequently by [001] slip. In compression, samples were deformed up to true strains of 1.83 (reductions up to 84%). The texture consisted of strong components of the compression axis near (100) and weaker components near (110). At higher strains the intensity of the near‐(100) components decreased, whereas the near‐(110) components became more intense. The near‐(100) components are explained by slip on (100) planes. The growth of the near‐(110) components at the expense of the near‐(100) components can be explained by relaxation twinning of the near‐(100) components.