bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mechanisms of frequency shifting in the infrared spectrum of stressed polymer
Authors: Wool Richard P. 
Published: April 2003

AbstractIn the vibrational spectrum of a polymer obtained under tensile stress loading conditions, several modes of molecular deformation can lead to different mechanisms of frequency shifting and asymmetric band deformation. Theoretically and experimentally it has been observed that quasielastic deformations (reduction of force constants due to bond weakening under stress), pure elastic bond stretching and angle bending, conformational variations, and several types of chain defects can cause linear shifts in frequency and infrared band distortion. A detailed study of the deformation spectra of isotactic polypropylene and polyphenyl‐p‐sulfide indicated that quasielastic and elastic mechanisms are the major contributors to frequency shifting, principally affecting stretching and bending vibrational modes. Conformational mechanisms can affect torsional modes whereas the defect mechanism, when present, can cause random distortion of an infrared band. The latter mechanism is difficult to quantize. The extent to which each mechanism contributes to the total spectral deformation can be a function of morphology, macroscopic loading conditions, thermal and strain histories.
Deformation and microstructure of extended‐chain polydiacetylene crystals
Authors: Baughman R. H. , Gleiter H. , Sendfeld N. 
Published: April 2003

AbstractThe mechanical properties (Young's modulus, ultimate tensile strength, deformation processes) of extended‐chain polydiacetylene crystals are investigated. The properties observed are similar to those of metal and ceramic whiskers. The elastic modulus is strain‐dependent and the ultimate tensile strength increases with decreasing crystal size. The maximum tensile strength observed was 1700 Nmm−2. The ultimate tensile strength seems to be controlled by the presence of a small number of defects near the surface at which fracture nucleates. Irreversible deformation of the crystals was observed to occur by crack propagation normal and parallel to the direction of the macromolecules. The observed mechanical behavior corresponds to exceptionally high per‐chain properties. The per‐chain modulus obtained for these crystals is nearly as high as that of diamond. A chain‐aligned polyethylene fiber with the same per‐chain mechanical properties would have an ultimate strength as high as 0.9 × 104 Nmm−2.
Ion clustering studies in poly(butadiene–styrene–4‐vinylpyridine) crosslinked by iron (III) chloride. Differential enthalpic analysis and electron microscopy
Authors: Pineri M. , Meyer C. , Bourret A. 
Published: April 2003

AbstractA terpolymer of butadiene–styrene–vinylpyridine has been crosslinked by addition of iron chloride. Differential enthalpic analysis gives evidence of a two‐phase system. Electron microscope studies at 0.1 and 1 MeV show the existence of precipitates. The majority of these ironrich aggregates have diameters less than 100 Å. Their form is polyhedral but very nearly spherical. No crystallinity has been detected inside the clusters. Thus the existence of strong interactions as in crystals of FeCl3 hydrates is excluded.
Pressure dependence of dielectric properties of chlorinated polyethylene vulcanizate. III. β relaxation
Authors: Naoki Motosuke , Nose Takuhei 
Published: April 2003

AbstractThe effects of temperature and pressure on the shift factor and the dielectric increment of the β relaxation process were measured for vulcanized chlorinated polyethylene. The isobaric and isochoric activation enthalpies, H*P and H*V, the activation volume V*, the pressure dependence of the glass–glass transition temperature, Tgβ/dP, and the apparent extinction temperature T0β were obtained. The pressure dependences of both V* and the dielectric increment would reach very small values near the liquid–glass transition temperature Tg, and the β process seems to be affected by the transition near Tg. The value of H*v/H*p for the β process is larger than that for the α process, and it is suggested that the molecular motions pertaining to the β process are more strongly restricted than those pertaining to the α process. The ratio T0β/T0, where T0 is the characteristic temperature in the Vogel–Fulcher–Tammann–Hesse equation for the α process, follows the empirical relation of Matsuoka and Ishida, Tgβ/Tg ∼0.75. The value of dTgβ/dP estimated from Tg and T0β/T0 is consistent with the experimental value.
Threshold fracture energies for elastomers
Authors: Ahagon A. , Gent A. N. 
Published: April 2003

AbstractFracture energies have been measured for two types of polybutadiene elastomer, crosslinked to various extents and torn under various conditions. Threshold values, ranging from 40 to 80 jm−2, were observed for samples torn at extremely low rates of tearing, at high temperatures, and in the swollen state. These values were found to be independent of temperature and rate of tearing, and also of the degree of swelling and the nature of the swelling liquid, provided a correction is made for the reduced areal concentration of molecular chains. They decreased somewhat with increased crosslinking, in good agreement with theoretical predictions of Lake and Thomas.6 The results for the two elastomers were substantially the same.These observations are strikingly different from those made at normal temperatures and rates of tearing, when large differences in fracture energy were observed between the elastomers, and between samples crosslinked to different extents, due to energy losses from nonequilibrium deformation processes in addition to the energy required for fracture.
Crystallization during polymerization of poly‐p‐xylylene. III. Crystal structure and molecular orientation as a function of temperature
Authors: Iwamoto Reikichi , Bopp Richard C. , Wunderlich Bernhard 
Published: April 2003

AbstractPolymerization of p‐xylylene was carried out from the gas phase with monomer produced by the pyrolysis of [2,2]‐p‐cyclophane. The crystalline form and preferred orientation of as‐polymerized polymer deposited at various temperatures (−196 to 80°C) were investigated by x‐ray diffraction methods. The melting behavior and other thermal transitions were studied by DSC. At 80°C the polymer film deposit is a mixture of the α and β forms, while between 60 and 0°C the deposit is of the α form. At lower temperature the polymer deposit is mainly of the β form, which shows diffuse reflections. At liquid nitrogen temperature it is of the β form with sharp reflections, contaminated with a small amount of oligomer. It was also found that at low temperatures, fibrillar crystals grow from the substrate in a direction 45° against the gas flow, and at even lower temperature, well‐oriented filmlike crystals grow perpendicular to the substrate surface.
Nucleation and growth of new crystals within polyethylene films during surface‐controlled recrystallization
Authors: Petermann J. , Gleiter H. 
Published: April 2003

AbstractObservations by transmission electron microscopy suggest that surface‐controlled recrystallization of polyethylene occurs by the solid state nucleation and growth of new crystals with (110) or (110) planes parallel to the free surface. The nucleation site of these crystals is the free surface. The growth process involves the migration of [002] tilt boundaries suggesting that these boundaries have high mobilities. The migration process may occur by the lateral rearrangement of the macromolecules in the [002] tilt boundary.
The orientation of amorphous chains in spherulites
Authors: Petraccone V. , Sanchez I. C. , Stein R. S. 
Published: April 2003

AbstractA theory for amorphous orientation in spherulitic polymers is presented based upon a consideration of conformational changes in the chains, loops, and cilia located between crystalline lamellae within a spherulite which is assumed to undergo an affine deformation. Chain statistics are worked out on the basis of (a) an analytical method involving random walks on a cubic lattice between barriers following a technique proposed by DiMarzio and Rubin and (b) a Monte Carlo computer simulation on a tetrahedral lattice. The latter method is considered more appropriate in view of the chain constraints such that lattice geometry becomes important. Values of the amorphous orientation are calculated as a function of the degree of crystallinity, initial lamellar separation, mole fraction of bonds in amorphous chains of each type, and chain lengths of each type of amorphous chain. It is found that tie chains are the principal contributor to amorphous orientation and the amount increases with increasing fraction and decreasing length of these. Results are compared with measurements of amorphous orientation by the birefringence x‐ray and the infrared dichroism technique. It is concluded that the tie chains must be initially quite highly elongated and that the assumed affineness of spherulite deformation is not closely obeyed.
Morphology of ultradrawn polyethylene strands. II. Nitric acid etching and melting behavior
Authors: Weeks Norman E. , Porter Roger S. 
Published: April 2003

AbstractA transparent, ultraoriented, high‐density polyethylene morphology has been produced by solid‐state (ultradraw) extrusion in a capillary rheometer. From the perspective of modulus and nitric acid etching behavior, the uniquely high draw ratios (<325) experienced by the polyethylene during extrusion result in a morphology with a high level of chain extension. The effect of nitric acid etching on strand thermal behavior has been determined by DSC. The observed melting points of unetched strands were sensitive to the thermal contact between sample and sample pan. Under conditions ensuring improved contact, strand superheating is reduced to one‐third of previously reported values. The negligible shrinkage evidenced by these strands up to 130° is consistent with the presence of a thermally stable component such as extended chain crystals or crystallized tie chains. The single, high‐melting peak is gradually replaced by a nonsuperheating, lower melting peak during the initial stages of acid etch. The resultant peak melting temperature is consistent with the value predicted for the peak crystal thickness of the etched polymer. No evidence is found for a higher melting peak attributable to the extended chain crystalline component. A highly constrained morphology produced by the large tie chain content is believed responsible for strand melting behavior. The melting point of the extended chain crystalline component is reduced by defects and a large ratio of lateral to basal surface area.
Computer simulation of brownian motion of a polyelectrolyte molecule (charged bead‐spring model)
Authors: Fujimori Susumu , Nakajima Haruhiko , Wada Yasaku , Doi Masao 
Published: April 2003

AbstractA Langevin equation of motion for a charged bead‐spring statistical chain is written in difference form and the relaxation and equilibrium behavior of the chain is studied by computer simulation. Results are presented for the behavior of end‐to‐end length h, principal axes of the polymer ellipsoid L1, L2, L3, and chain contour length c in terms of their averages, root mean square values, root mean square fluctuations, orientations, and relaxation strengths and times. The simulation was made with various sets of parameters, bead number N, charge on the bead q, and radius of ion atmosphere around the bead k−1. It is found that 〈h2〉1/2 and 〈L12〉1/2 increase more strongly with increasing q and decreasing κ than 〈L22〉1/2, 〈L32〉1/2, and 〈c12〉1/2, indicating that the chain is expanded in three dimensions and at the same time is extended along the end‐to‐end direction. The relaxation time τrot of rotation of the end‐to‐end vector, which is proportional to N2 at q = 0, increases with increasing q and tends to be proportional to N3 for an extended chain, while the relaxation time τconf of the magnitude of h is almost independent of q and is always proportional to N2. It is concluded that the extended chain possesses a well‐defined end‐to‐end axis and the chain rotates as a whole with a relaxation time τrot which is much longer than τconf. The complex viscosity of the chain is calculated from the Fourier transform of the time–correlation function of momentum flux and is found to have a frequency spectrum similar to that observed for aqueous solutions of poly(acrylic acid). The dominant mode appearing in the low‐frequency range is evidenced to arise from the rotation of the extended chain.
The crystal structure of poly(tetramethylene terephthalate)
Authors: Mencik Z. 
Published: April 2003

AbstractThe unit cell of poly(tetramethylene terephthalate) is triclinic with parameters a = 5.96 Å, b = 4.83 Å, c (fiber axis) = 11.62 Å, α = 115.2. β = 99.9, and γ = 111.3°; space group P1, calculated crystalline density 1.41 g/cc. The plane of the benzene ring is found to be inclined by about 15° from the fiber axis, contributing to a shortening of the fiber period as compared to the period expected on the basis of analogy with other members of the terephthalate ester series. The remaining shortening of the fiber period occurs in the O°CH2°CH2segment of the chain. No abnormally short distances among neighboring chain atoms were observed. A typical texture pattern was found in specimens of this polymer that were cold rolled and subsequently annealed. In this texture the c axis of the unit cell is highly oriented in the rolling direction; the a and b axes of the unit cell are oriented preferentially so that the terephthalate residue lies as close as possible to the plane of rolling.
Random‐coil dimensions of poly(methylphenylsiloxane) and their dependence on stereochemical structure
Authors: Mark J. E. , Ko J. H. 
Published: April 2003

AbstractRotational isomeric state theory was used to study the unperturbed dimensions 〈r2〉0 of poly(methylphenylsiloxane) (PMPS) chains [Si(CH3)(C6H5)O]x as a function of their stereochemical structure. The required conformational energies were obtained from semi‐empirical, interatomic potential energy functions and from known results on poly(dimethylsiloxane). PMPS chains were found to differ from monosubstituted and disubstituted vinyl chains primarily in the larger distance of separation between groups in conformations giving rise to “pentanetype interactions.” In PMPS, the relatively large distance of separation, 3.8 Å, makes such in teractions attractive, particularly in the case of two phenyl groups; in contrast, such interactions are strongly repulsive at the ∼2.5 Å separation characterizing vinyl chains. According to the calculated results, PMPS chains are very different from vinyl chains in that increase in isotacticity should cause a significant decrease in 〈r2〉0 and increase in d ln 〈r2〉0/dT. Comparison of theory with experimental results in the literature suggests that PMPS polymers which have been studied in this regard must have been significantly syndiotactic in stereochemical structure.
Dynamic mechanical properties of poly(2‐hydroxyethyl methacrylate) hydrogels
Authors: Nakamura Kunio , Nakagawa Tsurutaro 
Published: April 2003

AbstractHomogeneous and heterogeneous poly(2‐hydroxyethyl methacrylate) hydrogels were prepared by copolymerization of 2‐hydroxyethyl methacrylate and small amounts of ethylene glycol dimethacrylate in the presence of water; concentrations of water (V1) in the polymerization mixture and the volume fractions of water (v1) of the gels swollen to equilibrium were 40, 50, 60, 70% by volume, and 0.475, 0.541, 0.669, 0.778, respectively. From the homogeneous (clear) hydrogel (V1 = 40%) preparation, four hydrogels were prepared with v1 = 0.434, 0.418, 0.378, 0.326. Tensile dynamic moduli were measured in the frequency range from 0.006 to 0.6 cps and the temperature range from 0 to 40°C. In these cases, the influence of swelling on the shape of the relaxation spectra and on the monomeric unit friction coefficient was studied. The dependence of the friction coefficient on water concentration was interpreted in terms of free volume. In the heterogeneous (opaque) gel preparations (V1 = 50, 60, 70%), the effect of the aqueous phase in the system on the mechanical behavior was described by a modification of the blending law of Ninomiya. For the systems with V1 = 60% and 70% the shapes of the storage and loss moduli in the main transition region and the friction coefficient were similar to those of the homogeneous gel with V1 = 40%, except for the decrease in absolute value of the storage moduli. For the system with V1 = 50% the shape of the relaxation spectrum changes appreciably and the wedge distribution does not hold.
Studies of the amorphous region of polymers. II. Relationship between change of structure and glass‐transition temperature in polycarbonate
Authors: Ito Eiko , Hatakeyama Tatsuko 
Published: April 2003

AbstractA study of the effect of drawing on the glass transition temperature Tg of amorphous polycarbonate was carried out. The Tg attains a maximum at a draw ratio in the range from 1.6 to 2.0. The relationship between the change of structure and Tg is discussed in terms of the configurational entropy and the rate of molecular motion in local mode relaxation. The variation of Tg with drawing may be explained by using the iso‐entropy theory. The frequency of the maximum in the dielectric loss fmax and the dielectric relaxation strength Δε of the β mechanism changed with drawing in the same way as that of Tg. Based on the parallel behavior in these results, it is reasonable to consider that the β process of local mode relaxation of polyesters such as PC and PET reflects the structure of the glassy state.
The dynamic mechanical behavior of ultra‐high modulus linear polyethylenes
Authors: Smith J. B. , Davies G. R. , Capaccio G. , Ward I. M. 
Published: April 2003

AbstractThe dynamic mechanical properties of a number of ultra‐highly drawn polyethylenes have been studied over a wide range of temperature. It is shown that the materials possess low temperature Young's moduli as high as 1.6 Mbar, a figure which approaches the theoretical and experimental values for the c‐axis crystalline modulus of this polymer.The α and γ relaxation processes are still clearly discernible even at highest drawn ratios (ca. 35) and a quantitative analysis of the results, using structural data obtained from broad line nuclear magnetic resonance (NMR) measurements, suggests that the data are consistent with a modified series model.
Dielectric relaxations in polymers with pendent phenyl or pyridine groups at temperatures from 4°K to 80°K
Authors: Shimizu Kazuharu , Yano Okimichi , Wada Yasaku 
Published: April 2003

AbstractIsochronal measurements of dielectric loss are made for polystyrene (PS), poly(4‐vinyl pyridine) (P4VP), poly(2‐vinyl pyridine) (P2VP), poly(L‐phenylalanine) (PLPA), and poly(γ‐benzyl‐L‐glutamate) (PBLG) at temperatures ranging from 4°K to 80°K and at frequencies from 10 Hz to 100 kHz. PS, P4VP, and PLPA show loss peaks around 50°K (10 kHz) while P2VP exhibits a loss peak around 20°K (10 kHz). PBLG has no detectable peak in this temperature range. The 50°K and 20°K peaks are ascribed to wagging and rotation, respectively, of phenyl or pyridine groups between two energy minima. The barrier height and energy difference between the minima evaluated from the experimental data are reasonably explained by assuming that the double minima are caused by interaction between a pair of phenyl or pyridine groups, each belonging to adjacent chains which pack irregularly.
Heterogeneous nucleation of crystallization of high polymers from the melt. I. Substrate‐induced morphologies
Authors: Chatterjee A. M. , Price F. P. , Newman S. 
Published: April 2003

AbstractMelt crystallization of isotactic polypropylene (iPP), poly(ethylene oxide), poly(butene‐1), and polycaprolactone in contact with various substrates (mostly polymeric) has been studied by hot stage polarizing microscopy. Nucleating abilities of surfaces have been characterized qualitatively by examining the substrate‐induced morphologies of the crystallizing polymer. These morphologies have been classified into three groups, depending on whether the substrate is very active (transcrystallinity), moderately active, or inactive as a nucleating agent. The morphologies observed are temperature‐dependent, changing from transcrystalline to spherulitic upon increase of the crystallization temperature. At intermediate temperatures, mixed surface morphologies (transcrystalline plus spherulitic) are observed.The concentration of titanium and aluminum catalytic residues in isotactic polystyrene (iPS) samples can be reduced by two methods, i.e., (a) fractionating the polymer and (b) chelating Ti and Al with acetylacetone. The high nucleating ability of iPS samples in the crystallization of iPP has been shown to be due to the polymer (iPS) itself, and not to Ti and Al residues. Apart from iPS, other polymers (low energy surfaces) have also been found to induce transcrystallinity.From a survey of 43 substrate‐crystallizing polymer pairs, conclusions have been drawn which are relevant to the following potential factors in heterogeneous nucleation processes: (a) chemical structure, (b) crystallographic unit cell type, (c) lattice parameters, (d) crystallinity of substrate, and (e) surface energy of substrate.
Quasielastic scattering by dilute polymer solutions
Authors: Akcasu Z. , Gurol H. 
Published: April 2003

AbstractThe scattering law S(k,w) for dilute polymer solutions is obtained from Kirkwood's diffusion equation via the projection operator technique. The width Ω(k) of S(k,w) is obtained for all k without replacing the Oseen tensor by its average (as is done in the Rouse–Zimm model) using the “spring‐bead” model ignoring memory effects. For small (ka\documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt N $ \end{document} ≪ 1) and large (ka ≫ 1) values of k we find Ω = 0.195 k2/β α η0 \documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt N $ \end{document} and Ω = k2/βξ, respectively, indicating that the width is governed mainly by the viscosity η0 for small k values and by the friction coefficient ξ for large k values. For intermediate k values which are of importance in neutron scattering we find that in the Rouse limit Ω = k4a2/12βξ. When the hydrodynamic effects are included, Ω(k) becomes 0.055 k3/βη0. Using the Rouse–Zimm model, it is seen that the effect of pre‐averaging the Oseen tensor is to underestimate the half‐width Ω(k). The implications of the theoretical predictions for scattering experiments are discussed.