bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractStress‐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

AbstractThe 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

AbstractEthylene 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

AbstractA 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

AbstractPolybutadiene 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

AbstractCrystals 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

AbstractCrystal 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

AbstractGel 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

AbstractThe 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

AbstractFrictional 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

AbstractA 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

AbstractThe 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.
Polymerization of N‐carboxy–amino acid anhydrides in the solid state. II. Relation between polymerizability and molecular arrangement in L‐leucine NCA and L‐alanine NCA crystals
Authors: Kanazawa Hitoshi , Ohashi Yuji , Sasada Yoshio , Kawai Tohru 
Published: April 2003

AbstractThe polymerizability of N‐carboxy–amino acid anhydrides (NCAs) of L‐leucine and L‐alanine was examined in the solid state and in solution. L‐leucine NCA shows much higher reactivity in the solid state (when immersed in hexane) than in solution (in acetonitrile), but the opposite is true for L‐alanine NCA. However, the two NCAs give similar values of apparent activation energy in each polymerization system. Rather high‐molecular‐weight polypeptides were obtained in the polymerization of L‐leucine NCA in the solid state compared with those obtained in solution, while the molecular weight of polymers obtained from L‐alanine NCA was higher in solution than in the solid state. IR spectra showed that α helices form mainly in the polymerization of both L‐leucine NCA and L‐alanine NCA in the solid state; a small amount of the β structure forms in the latter polymerization. X‐ray diffraction and electron microscopy revealed that L‐leucine NCA polymerizes predominantly along the c axis in the crystal, while the polymer chains grow in random directions in the crystal of L‐alanine NCA. The difference can be explained by the molecular arrangement in the crystal. There are two requirements for high reactivity in the solid state: the five‐membered rings of the monomer must form a layer structure and the polymer must occupy nearly the same space as the reacting monomer.
Bisphenol‐A polycarbonate–poly(butylene terephthalate) transesterification. III. Study of model reactions
Authors: Devaux J. , Godard P. , Mercier J. P. 
Published: April 2003

AbstractExchange reactions in molten bisphenol‐A polycarbonate–poly(butylene terephthalate) mixtures are investigated by means of model reactions. Transesterification can result either from direct ester‐ester interchange or via alcoholysis or acidolysis. Among the various reactions investigated, only the PBTP alcoholysis by phenol is not found to occur. Taking into account that bisphenol‐A terephthalate units (A2B1) and butylene carbonate units (A1B2) are formed in equimolecular amounts, it is concluded that direct ester‐ester interchange is the most likely mechanism for PC‐PBTP transesterification.
Bisphenol‐A polycarbonate–poly(butylene terephthalate) transesterification. IV. Kinetics and mechanism of the exchange reaction
Authors: Devaux J. , Godard P. , Mercier J. P. 
Published: April 2003

AbstractThe kinetic aspects of the bisphenol‐A polycarbonate–polybutylene terephthalate exchange reaction are considered as a function of temperature and of the PC/PBTP ratio. The most likely mechanism is a direct reversible ester‐ester interchange reaction catalyzed by titanium residues present in commercial PBTP.
Phase behavior of the quasiternary system N‐methylmorpholine‐N‐oxide, water, and cellulose
Authors: Chanzy H. , Nawrot S. , Peguy A. , Smith P. , Chevalier J. 
Published: April 2003

AbstractThe crystallization and melting behavior of the system N‐methylmorpholine‐N‐oxide (MMNO)–H2O–cellulose has been studied by differential scanning calorimetry, optical and electron microscopy, and x‐ray scattering. The phase diagram of the MMNO–H2O solvent system is reported up to a water content of 28% w/w. MMNO forms two crystalline hydrates, namely a monohydrate (13,3% w/w H2O) and a hydrate comprising five molecules of crystal water per two MMNO molecules (28% w/w H2O), which melts at 78°C and 39°C, respectively. The melting points of the various diluent crystals are strongly depressed in the presence of cellulose. For example, the solvent liquidus curve in the quasibinary system MMNO.1H2O–cellulose can be described very well using the simple Flory–Huggins expression with an interaction parameter χ = −3. Finally, the MMNO‐rich part of the melting point/composition diagram of the quasiternary MMNO–H2O–cellulose system is constructed and discussed.
Dynamics of rodlike polymers in semidilute solutions: Short‐time‐scale motion
Authors: Doi Masao 
Published: April 2003

AbstractA new kinetic equation which describes the rotational Brownian motion of rodlike polymers in concentrated solution is proposed on the basis of the tube model. The equation takes into account the two types of rotational motion, i.e., (i) the slow diffusion due to the reptation‐rotation process, and (ii) the rapid fluctuation of the polymer inside the tube. This equation explains the recent experimental finding by Mori et al. that the dc component of the dynamic Kerr constant changes sign from positive to negative at high frequency.
The β relaxation behavior of bisphenol‐type resins
Authors: Takahama T. , Geil P. H. 
Published: April 2003

AbstractThe β relaxation of a phenoxy resin and a number of related uncured and cured bisphenol‐type epoxide resins was studied using a torsion pendulum. Two molecular mechanisms are proposed to contribute to the β relaxation in the range from −55 to −80°C. One is the motion of the hydroxyether group and the other is related to motions of the crosslink itself. The β‐relaxation peak temperature was found to increase with the concentration of hydroxyether groups in the matrix. Motion of the crosslinks in the matrix gives rise to a contribution to the β peak at −80°C. In addition, motion of the diphenyl propane group is proposed to result in a relaxation process at ca. −110°C.
Aging of piezoelectricity in poly(vinylidene fluoride)
Authors: Kolbeck A. G. 
Published: April 2003

AbstractThis report describes isothermal aging of piezoelectricity in poly(vinylidene fluoride) (PVDF) based on long‐term heat treatments between 40 and 160°C. The results demonstrate that no piezoelectric decay occurs below about 60°C, that between 60 and 160°C the aging behavior follows logarithmic kinetics, and that aging is linearly dependent on temperature. Both uniaxial and biaxial PVDF show similar trends, but piezoelectric decay is more rapid for uniaxial film. Decay of permanent poling‐induced polarization is identified as the likeliest cause of piezoelectric aging, and piezoelectric decay is found to be associated with long‐range annealing effects which also produce macroscopic shrinkage of the PVDF film.
An unusual fatigue crack‐tip plastic zone: The epsilon plastic zone of polycarbonate
Authors: Takemori Michael T. , Matsumoto Dean S. 
Published: April 2003

AbstractPolycarbonate exhibits an extraordinary crack‐tip plastic zone under certain fatigue loading conditions. During discontinuous growth (multiple load cycles per crack jump), the plastic zone consists of a leading craze and a pair of sharply delineated shear bands, which together look like the Greek letter epsilon. The kinetics of the development of the epsilon plastic zone and the nature of the transition from discontinuous growth to a shear fatigue fracture mode are discussed.
Tensile strength of filled polymers
Authors: Chow T. S. 
Published: April 2003

AbstractA model is developed to predict the ultimate tensile strength of a particulate‐filled polymer which depends not only on the volume fraction of the filler and the elastic moduli of the two material phases, but also on the shape, size, and interfacial adhesion between the filler particle and the matrix. The effects of these parameters have been examined and attempts have been made to compare them with those available in the literature. Considering the complexity of fracture, the theoretical prediction is in reasonably good agreement with published experimental data.
End effects for a rodlike polyelectrolyte molecule in salt solution
Authors: Katoh T. , Ohtsuki T. 
Published: April 2003

AbstractElectrostatic potentials around a single rodlike polyelectrolyte molecule are calculated by solving the nonlinear Poisson–Boltzmann equation numerically in the presence of externally added salt. The polyion is regarded as a cylinder with a finite length whose side surface is uniformly charged and end surfaces uncharged. The calculations show that the distance to which end effects extend is about half the Debye screening length and is almost independent of the surface charge density and concentration of added salt. For a long polyion whose length is much greater than the Debye length, the end effects can be neglected even for a polyelectrolyte with high surface charges, whereas they play an important role for a short polyion with a length of the same order as the Debye length. In addition, a strong charge condensation is found in the direction of the axis of the cylinder for a long polyion.
Effects of carbon filler on sorption and diffusion of gases through rubbery materials
Authors: Tanioka Akihiko , Oobayashi Atsushi , Kageyama Yuji , Miyasaka Keizo , Ishikawa Kinzo 
Published: April 2003

AbstractEffects of carbon filler on the sorption and diffusion of carbon dioxide in natural rubber and in styrene‐butadiene rubber have been studied. Sorption isotherms conform to Henry's law in unfilled rubber and to Langmuir's law in carbon black. The isotherms in filled rubber exhibit a combination of the two sorption modes. The Henry's law solubility parameter kD increases with carbon filler content; the Langmuir saturation constant C′A initially is constant with filler level, but then decreases abruptly when carbon particles begin to aggregate. The diffusion coefficient decreases with increasing filler content, presumably owing to geometric effects and to polymer chain immobilization in the interfacial regions.
Light‐scattering studies of phase‐demixing of polystyrene/poly(o‐chlorostyrene) blends
Authors: Gilmer John , Goldstein Niel , Stein Richard S. 
Published: April 2003

AbstractThe phase separation of blends of polystyrene and poly(o‐chlorostyrene) has been studied by observing the changing small‐angle light‐scattering profile with time. As a blend is heated to a temperature at which it undergoes phase separation, a light‐scattering maximum is observed which grows in intensity and moves to smaller angles with time. This maximum is associated with a characteristic spacing which increases at a rate which becomes greater at higher temperature or with lower molecular weight. This spacing varies with a power of time as might be expected for domain growth occurring by a viscous flow mechanism. The integrated scattering intensity (invariant) is found to increase initially with time and then remain constant, as is characteristic of phase separation followed by phase ripening.
Spectroscopic characterization of the rotational conformations in the disordered phase of poly(ethylene terephthalate)
Authors: Lin Shaow‐Burn , Koenig Jack L. 
Published: April 2003

AbstractRecently developed data processing techniques have been applied to determine the complete spectra of the trans and gauche isomers of PET and to use these spectra to determine the conformational composition of PET samples isothermally crystallized from the glassy state between 75 and 240°C. A linear correlation was found between normalized absorbance of conformational bands and density measurements, with the trans bands showing a positive slope and the gauche bands a negative slope. Extrapolation of the results from trans bands to zero percent of trans yields the density of the pure gauche isomer, 1.326 ± 0.002 g/cm3. Similarly, from the gauche bands the density of 100% crystalline trans is found to be 1.510 ± 0.014 g/cm3. Meanwhile, the density of the amorphous trans is calculated to be 1.430 ± 0.003 g/cm3. From these values and the combined density and infrared measurements, the content of trans isomers in the amorphous phase is calculated. It is found that the content of amorphous trans is a function of both annealing temperature and time. It is observed that the amorphous trans content decreases as the crystalline trans content increases. At high crystallinity, the amorphous trans content approaches zero. These amorphous trans isomers are associated with the extended units making up the interlamellar links. The loss of these extended trans interlamellar links is reflected in the mechanical properties of PET.
Quantitative analysis of polymers by attenuated total reflectance fourier‐transform infrared spectroscopy: Vinyl acetate and methyl content of polyethylenes
Authors: Mirabella Francis M. 
Published: April 2003

AbstractA comparison was made between the transmission and attenuated total reflectance (ATR) infrared spectroscopic techniques for the determination of the vinyl acetate content of poly(ethylene–vinyl acetate) copolymers and methyl content of polyethylene. It was demonstrated that the transmission and ATR calibration curves for ratios of absorbances of bands with maxima at very similar wavelength were coincident, while those for ratios of absorbances of bands with maxima at significantly dissimilar wavelength were shifted apart. The explanation of this behavior is based on the wavelength dependence of the interaction of the IR radiation in ATR, compared to the wavelength independence of the interaction in transmission IR. The effect of polarized radiation was investigated in each type of analysis with the ATR technique. It was found that essentially the same results were obtained with the IR radiation polarized at 0° or 90°, relative to the plane of incidence, as compared to spectra obtained with unpolarized radiation. However, larger scatter was observed with polarized radiation. The effect of clamping pressure was also investigated. It was found that a minimum clamping torque of 5 in. lb is necessary to assure good physical contact in ATR work.