bluuebunny/crossref_metadata_2025_split huggingface dataset:
Crack velocity dependence of electron emission during fracture of filled elastomers
Authors: Dickinson J. T. , Jensen L. C. 
Published: April 2003

AbstractIn this article we examine the electron emission accompanying the fracture of filled elastomers, where in previous work we have shown the emission to be intense and due predominately to interfacial failure. In this study we show that there is a strong velocity dependence on the rate of electron emission during the propagation of a crack in filled silicone rubber and polybutadiene filled with glass beads. This dependence cannot be explained by a simple proportionality between emission rate and rate of surface area production. We propose that the concentration of free radicals produced by crack propagation increases rapidly with crack velocity which in turn produces more intense electron emission by a chemiemission mechanism.
The dependence of the glass transition temperature of poly(N‐vinylcarbazole) upon steric microstructure and molecular weight
Authors: Terrell D. R. , Evers F. , Smoorenburg H. , van den Bogaert H. M. 
Published: April 2003

AbstractPoly(N‐vinylcarbazole) (PVK) samples were found to exhibit up to three glass transition temperatures Tg, corresponding to the whole chain and the syndiotactic and isotactic stereoblocks. An increasing tendency to multiple Tgs, and hence to phase separation, was observed with increasing isotacticity. Limiting values at infinite molecular weight for syndiotactic and isotactic PVK were obtained from correlations of the Tgs corresponding to the syndiotactic and isotactic stereoblocks with their respective average stereoblock lengths derived from 13C NMR measurements. They were found to be 549 and 399 K, respectively. The conventional Tg for PVK was found to exhibit the following dependence upon the syndiotactic dyad mole fraction Xs:

The molecular weight dependences of the conventional Tgs for several fractionated PVK samples obeyed a Fox–Flory‐type relation with values of −dTg/d(1/M) varying between 7.6 × 103 for isotactic PVK and 2.7 × 105 for Luvican M 170.
Multiphase equilibria in solutions of polydisperse homopolymers. I. Three‐phase equilibria in ternary and quasiternary systems
Authors: Šolc Karel 
Published: April 2003

AbstractA recent critique of the mechanism of three‐phase separation suggested by Tompa for ternary system solvent–polymer (1)–polymer (2) is shown to be invalid, and Tompa's account is reinforced by analytical arguments and numerical results. In particular it is proven that the critical point in some simple Flory–Huggins systems is thermodynamically unstable, rather than just metastable. Three‐phase separations in quasiternary systems cannot be studied by simple methods advanced for treatment of true ternary systems. Rather a new, more general, approach is required for these cases.
The nonlinear viscoelastic behavior of a carbon‐black‐filled elastomer
Authors: Sullivan J. L. , Demery V. C. 
Published: April 2003

AbstractThe stress relaxation behavior of a carbon‐black‐filled elastomer is shown to be independent of the state of deformation, and the temperature dependence of its static modulus is in good accord with that predicted by the statistical theory of elasticity. The storage and loss moduli are found to be separable functions of frequency and overall strain effects in both simple tension and pure shear. A separability of static deformational and dynamic strain amplitude effects is found for the storage modulus, but could not be determined for the loss modulus. However, the loss tangent is found to be a function of the static state of deformation. From these experimental results, it is shown that an existing viscoelasticity theory for an unfilled system when specialized to uniaxial extensions has a form which can be made suitable for representing the dynamic behavior of filled systems by the introduction of two functions of the dynamic strain amplitude.
Spectroscopic characterization of the matrix–silane coupling agent interface in fiber‐reinforced composites
Authors: Chiang Chwan‐Hwa , Koenig Jack L. 
Published: April 2003

AbstractThe copolymerizations of anhydride‐cured epoxy resin on fiberglass surfaces treated with a N‐methylaminopropyltrimethoxysilane coupling agent has been investigated using Fourier‐transform infrared spectroscopy. The structure of the interface of the silane and the resin in fiber‐reinforced composites is composed of copolymers of the epoxy resin with the organofunctionality of the deposited silanes. The number of interfacial bonds formed depends on the amount of silane coupling agent deposited on the fiberglass and the reaction conditions. The silane induces additional esterification and increases the curing density of the epoxy matrix near the fiber surface by about 5–10% relative to the bulk resin.
Study of molecular motion in polysilastyrene by pulsed 1H nuclear magnetic resonance
Authors: McGarvey Bruce R. , Schlick Shulamith 
Published: April 2003

AbstractPulsed NMR spectra of protons in polysilastyrene, $ \rlap{--} [{\rm Si(CH}_{\rm 3} {\rm )}_{\rm 2} {\rm &#x0F8FF; Si(CH}_{\rm 3} )({\rm C}_6 {\rm H}_5 )\rlap{--} ]_n $, with n ≈ 60, have been measured in the temperature range 80–450 K. The linewidth is constant at 7.4 G up to 200 K and narrows considerably above 250 K to a constant value of 0.3 G above 360 K. The motion responsible for this effect has an activation energy of 43.7 kJ/mol and is identified with the large‐scale motion occurring in the vicinity of the glass transition temperature. The spin‐lattice relaxation time T1 was measured by the π‐t‐½π pulse sequence as a function of temperature. Two motional minima in T1 were observed. The low‐temperature motion has an activation energy of 3.7 kJ/mol and is identified with methyl group reorientation. The high‐temperature motion has an activation energy of 29.1 kJ/mol and might be due to segmental motion.
Morphology of CaCO3‐filled polyethylenes
Authors: Chacko V. P. , Karasz F. E. , Farris R. J. , Thomas E. L. 
Published: April 2003

AbstractThe morphology of one novel “homogeneous composite” and some conventional CaCO3‐particulate‐filled polyethylenes (PEs) has been investigated by transmission and scanning electron microscopy. It is found that for three different linear polyethylenes (Mw = 37,000, 200,000, and 1.5 × 106) studied, ordering on the scale of spherulites was absent in the CaCO3‐filled polymer. However, PE lamallae were observed growing normal to the filler interface. Changes in molecular weight of the polyethylene result in easily observed differences in morphology, while DSC studies indicate that crystallinity decreases in the presence of filler for the two lower‐molecular‐weight polyethylenes.
Molecular design of multicomponent polymer systems. III. Comparative behavior of pure and tapered block copolymers in emulsification of blends of low‐density polyethylene and polystyrene
Authors: Fayt R. , Jérôme R. , Teyssié Ph. 
Published: April 2003

AbstractPoly(hydrogenated butadiene‐b‐styrene) copolymers are very effective emulsifiers for blends of polystyrene and low‐density or high‐density polyethylene. It is shown that the extent of improvement in mechanical properties is dependent not only on the molecular weight but also on the structure of the diblock copolymer. A comparative study of the morphology and the mechanical behavior of modified low‐density polyethylene/polystyrene blends demonstrates that a tapered diblock is more efficient than a pure diblock with the same composition and molecular weight. It is assumed that the unique behavior of the tapered sample results from its particular miscibility characteristics at the blend interface. The tapered copolymer could behave essentially as a solu‐bilizing agent for the homopolymers at the interface and provide a “graded” modulus responsible for the improved mechanical response of the material.
Tensile strength of highly oriented polyethylene. II. Effect of molecular weight distribution
Authors: Smith Paul , Lemstra Piet J. , Pijpers Jacques P. L. 
Published: April 2003

AbstractThe tensile strength of oriented polyethylene filaments is discussed in relation to molecular weight. Short‐term tensile properties at room temperature were obtained in our laboratory and from the literature for polymer samples covering the molecular weight (Mw) range from 54 × 103 to 4 × 106, and polydispersities ranging from 1.1 to 15.6, oriented by solid‐state extrusion, melt spinning/drawing, solution spinning/drawing, and “surface growth.” It was found that both the molecular weight and its distribution markedly affected tensile strength. The breaking stress σ of highly oriented fibers varied with molecular weight roughly as σ ∝, M0.4, at constant Mw/Mn over the entire range studied. Reduction of polydispersity from 8 to 1.1 by an increase of Mn with Mw approximately constant at 105 increased tensile strength of oriented polyethylene filaments by a factor of nearly 2.
On the use of Raman‐active longitudinal acoustic modes in the study of polyethylene lamellar structures
Authors: Glotin M. , Mandelkern L. 
Published: April 2003

AbstractThe first‐, third‐, and fifth‐order low‐frequency, Raman‐active, longitudinal acoustical modes of the n‐alkane C94H190 and different morphological forms of semicrystalline polyethylene have been obtained. An analysis of the results shows that the correction needed to obtain the extended planar‐zigzag ordered sequence length is maximum for the n‐alkane and very small for the polymer systems. These represent solution crystals as well as bulk‐crystallized material. For the latter, samples were prepared so that the crystallite thickness is either comparable to or very much smaller than the extended chain length. An approximate method is also developed which enables the natural linewidth to be determined.
Structure‐property relationships in polycaprolactone‐polyurethanes
Authors: Van Bogart John W. C. , Gibson Philip E. , Cooper Stuart L. 
Published: April 2003

AbstractThe structure‐property relationships of polycaprolactone‐based segmented polyurethanes were studied using differential scanning calorimetry (DSC), small‐angle x‐ray scattering (SAXS), wide‐angle x‐ray diffraction (WAXD), dynamic mechanical, and stress‐strain testing. The materials studied varied in hard‐segment type [4,4′‐diphenylmethane diisocyanate/butanediol (MDI/BD) or 4,4′‐dicyclohexyl methane diisocyanate/butanediol (H12MDI/BD)], soft‐segment molecular weight (830 or 2000 MW polycaprolactone), hard‐segment content (23–77% by weight), and thermal history. The materials with aromatic (MDI/BD) hard segments had semicrystalline hard‐segment domains, while the materials with aliphatic (H12MDI/BD) hard segment had mostly amorphous domains. Materials with the shorter polycaprolactone soft segment (830 MW) exhibited thermal and mechanical behavior which indicated a considerable degree of hard‐ and soft‐segment compatibility. The materials which contained a 2000‐MW polycaprolactone soft segment exhibited better‐defined microphase separation. SAXS was used to characterize the microphase structure of each system. The effects of hard‐segment content and soft‐segment molecular weight were similar for the aromatic (MDI) and aliphatic (H12MDI) hard‐segment‐based block copolymers. Changing the hard segment from aromatic to aliphatic gave materials with larger interfacial area and slightly higher tensile strength. A range of morphologies between isolated hard domains in a rubbery matrix and isolated rubbery domains in a hard matrix was observed.
A structural model for high‐modulus polyethylene derived from entanglement concepts
Authors: Grubb D. T. 
Published: April 2003

AbstractStarting from the concept that the entanglement network is a controlling factor in polymer deformation, a molecularly based model has been constructed for polyethylene, drawn or extruded to high extension ratios λ. It predicts the experimentally observed form of the increase of Young's modulus E with λ: E−1 = B + Cλ−2. The model structure consists of imperfect crystalline microfibrils 10‐30 nm in diameter and length αλ2, about 1 μm at λ = 30. The microfibrils terminate at clusters of entanglements, and are embedded in a matrix of low modulus. This structure is very similar to that derived from solution‐grown shish‐kebab material. Available melting‐point data for highly extended material fit the structural model well.
Unsuccessful search for a liquid‐liquid transition in compression isotherms of polystyrene
Authors: Loomis L. D. , Zoller Paul 
Published: April 2003

AbstractIn a search for a liquid‐liquid transition in the melt of polystyrene, we have measured and analyzed a number of compression isotherms to 1800 kg/cm2 in a relevant temperature range (1.2Tg < T < 1.4Tg). Volume data were recorded at pressure intervals of 10 kg/cm2, i.e., at pressure intervals 5‐20 times smaller than used in previous work. For the analysis the data were fitted to the Tait equation. Deviations between fits and data are small, typically 0.0004 cm3/g, but nonrandom. From the absence of any systematic shifts of the nonrandom deviation patterns with temperature, we conclude that the deviations are not manifestations of a pressure‐dependent liquid‐liquid transition, and that there is, in fact, no evidence for the existence of such a transition in our data.
Polymorphic structure and physical properties of the polyester/ether poly(ethylene‐1,2‐diphenoxyethane‐p,p′ ‐dicarboxylate)
Authors: Shimizu Jiro , Okui Norimasa , Imai Yoshitaka , Nishide Shingo , Takaku Akira 
Published: April 2003

AbstractX‐ray diffraction studies of fibers of the polyester/ether poly(ethylene‐1,2‐diphenoxyethane‐p,p′ ‐dicarboxylate) (PEET) produced by high‐speed melt spinning show the existence of two polymorphic forms, designated α and β, in the solid state. The α form is obtained by annealing filaments melt spun at takeup speeds below 3000 m/min and is also found in samples crystallized from the melt and from dilute solutions. The α form has a monoclinic unit cell with dimensions a = 7.83, b = 10.33, c = 18.68 Å, and β = 83.1°. The equilibrium melting temperature and heat of fusion of the α form are 288.3°C and 19.1 cal/g, respectively. The β form predominates in highly oriented filaments obtained at takeup velocities above 6000 m/min. The unit cell is orthorhombic with dimensions a = 7.28, b = 5.65, and c = 18.64 Å. The β form does not transform to the α form on annealing.
A Raman‐spectroscopic study of solution‐crystallized polyethylenes
Authors: Glotin M. , Domszy R. , Mandelkern L. 
Published: April 2003

AbstractAn analysis of the Raman internal modes of dilute‐solution‐crystallized homopolymers and co‐polymers of ethylene has been made, similar to the work previously reported for the bulk‐crystallized polymers. The crystallite structure can be described in terms of the relative amounts of the crystalline orthorhombic phase, the liquidlike amorphous phase, and the interfacial region. These quantities change with the molecular constitution of the chains and the crystallization conditions. The level of crystallinity decreases significantly with increasing counit content as would be expected. In addition, an appreciable interfacial structure develops in copolymers as compared with the homopolymers. A possible relationship between the interfacial content and the relaxation transitions in polyethylene is discussed.
The heat of fusion of poly(ethylene terephthalate)
Authors: Starkweather Howard W. , Zoller Paul , Jones Glover A. 
Published: April 2003

AbstractBy use of the Clapeyron equation for the dependence of the melting point on pressure, the heat of fusion was found to be 32.5 cal/g, in good agreement with values determined by other methods. An equation for the dependence of the melting point on the degree of polymerization gave a heat of fusion of 27.6 cal/g when applied to hydroxyl‐terminated oligomers. This simple relation applied all the way down to the smallest member of the series, di(hydroxy ethyl) terephthalate.
Further annealing studies of the calcium salt of an ethylene‐methacrylic acid copolymer
Authors: Brozoski B. A. , Coleman M. M. , Painter P. C. 
Published: April 2003

AbstractAnnealing studies of the calcium salt of an ethylene‐methacrylic acid copolymer are reported. Fourier‐transform infrared spectroscopy and differential scanning calorimetry were applied to the investigation of the effect of polyethylene crystallization on ionic structure as a function of annealing temperature and time. The spectroscopic changes observed in the spectra of the calcium salt annealed at 80°C differ from those seen in the spectra of the calcium salt annealed at room temperature. These changes are interpreted in terms of the multiplet‐cluster model and the effect of the polyethylene‐type crystallinity on the ionic microstructure.
Chain folding in single crystals of polytetrafluoroethylene
Authors: Giglio E. , Morosetti S. , Palleschi A. , Pavel N. V. 
Published: April 2003

AbstractPotential‐energy calculations are performed in order to obtain satisfactory models for folding in single crystals of polytetrafluoroethylene crystallized in the phase stable below 19°C. The folds are assumed to be tight with adjacent reentry. Folds with a variable number of bonds are analyzed. Their conformation is deduced by a method which obtains closure between two semifolds into which each fold is decomposed. The allowed models are subsequently investigated by using an energy minimization program. Some possible models are proposed. The calculations show that the folds must be described by a number of rotational isomeric states higher than is usually assumed.
Dynamic x‐ray diffraction studies of high‐density polyethylene
Authors: Cembrola Robert J. , Kyu Thein , Stein Richard S. , Suehiro Shoji , Kawai Hiromichi 
Published: April 2003

AbstractDynamic x‐ray diffraction is conducted to explore the structural origin of the α and β mechanical dispersions of a melt‐crystallized high‐density polyethylene. It is shown that the real component of the strain orientation coefficient for the crystal c axis C decreases with increasing frequency at a rate which decreases with decreasing temperature. Values of C for the c axis are positive, C for the a axis negative, and C for the b axis close to zero, suggesting that the predominant relaxation process is crystal rotation about the b axis. The activation energy found from Arrhenius plots of C corresponds to that of the α1 mechanical dispersion. The dynamic birefringence in this region is dominated by the contribution from crystal orientation changes. At low temperatures, the imaginary component KC of the strain‐optical coefficient of the crystal phase approaches zero, while KC of the amorphous phase exhibits a somewhat broad dispersion peak corresponding to the β birefringence dispersion. This suggests that the principal contribution to the β birefringence dispersion arises from the amorphous phase, probably owing to the amorphous orientation process. Contrary to the case of low‐density polyethylene, the dynamic crystal lattice deformation and compliance functions reveal distinct frequency dispersions corresponding to the α1 and α2 mechanical processes. The α1 lattice dispersion is thought to be associated with the α1 crystal orientation dispersion, while the α2 lattice dispersion is believed to be the inherent one arising from the onset of intracrystalline chain motions.
The use of small‐angle electron scattering to compare the structure of craze found in thin films with that found in bulk materials
Authors: Brown H. R. 
Published: April 2003

AbstractSmall‐angle electron scattering (SAES) has been used to examine the structure of crazes in polystyrene. It has been shown theoretically that the analysis of SAES is similar to the equivalent x‐ray patterns (SAXS) except perhaps for the higher‐angle scattering. A direct comparison of the SAES patterns from crazes in films of ca. 400 nm thickness with SAXS patterns from crazes in films of ca. 1 mm thickness has shown that the craze structures are similar in form for the thin and thick films but the fibrils are about three times larger in the thin films.
Electrical properties of ion‐implanted poly(p‐phenylene sulfide)
Authors: Mazurek H. , Day D. R. , Maby E. W. , Abel J. S. , Senturia S. D. , Dresselhaus M. S. , Dresselhaus G. 
Published: April 2003

AbstractIon implantation of impurities into thin films of poly(p‐phenylene sulfide) (PPS) is found to increase the conductivity of the material by up to 12 orders of magnitude. The increase is stable under exposure to ambient conditions, in contrast to the instability of the conductivity increases in PPS produced by chemical doping with AsF5. PPS films 0.1–0.2 μm thick are spin cast from solution onto interdigitated electrodes patterned on an oxidized silicon substrate. The room‐temperature interelectrode resistance is measured as a function of implantation fluence. An estimate of film conductivity is obtained from this resistance with a simple model for the electrode and film geometry. A first experiment yielded similar conductivity increases for implantation of either arsenic or krypton. At a fluence of 1 × 1016cm−;2, which corresponds to an average impurity concentration of 2.5 × 1021cm−3, the conductivity reaches an apparently saturated value of 1.5 × 10−5 (Ω cm)−1. Infrared spectra of the films before and after implantation suggest that crosslinking may be present in the implanted films, and Auger studies show stoichiometric changes throughout the implanted layer. These results suggest that the observed conductivity changes are the result of molecular rearrangements produced by the implantation rather than the result of specific chemical doping. Specific chemical doping may, however, explain the results of a second experiment in which implantation of bromine resulted in substantially larger conductivities found to increase at an approximate linear rate from a value of 1.0 × 10−4 (Ω cm)−1 at a fluence of 1 × 1016 cm−2 to a value of 4.0 × 10−4 (Ω cm)−1 at a fluence of 3.16 × 1016 cm−2.
Photon correlation spectroscopy of polystyrene as a function of temperature and pressure
Authors: Patterson G. D. , Carroll P. J. , Stevens J. R. 
Published: April 2003

AbstractPhoton correlation spectroscopy is employed to study the slowly relaxing density and anisotropy fluctuations in bulk atactic polystyrene as a function of temperature from 100 to 160°C and pressure from 1 to 1330 bar. The light‐scattering relaxation function is well described by the empirical function ϕ(t) = exp[−(t/τ)β], where for polystyrene β = 0.34. The average relaxation time is determined at each temperature and pressure according to 〈τ〉 = (τ/β)Γ(1/β) where Γ(x) is the gamma function. The data can be described by the empirical relation 〈τ〉 = 〈τ〉0 exp[(A + BP)/R(T − T0)] where R is the gas constant and T0 is the ideal glass transition temperature. The empirical constant A/R is in good agreement with that determined from the viscosity or the dielectric relaxation data (1934 K). The empirical constant B can be interpreted as the activation volume for the fundamental unit involved in the relaxation and is found to be comparable to one styrene subunit (100 mL/mol). The quantity B appears to be a weak function of temperature. The use of pressure as a tool in the study of light scattering near the glass transition now has been established.