bluuebunny/crossref_metadata_2025_split huggingface dataset:
High‐Pressure phase behavior of mixtures of poly(ethylene‐co‐methyl acrylate) with low‐molecular weight hydrocarbons
Authors: Hasch Bruce M. , Meilchen Melchior A. , Lee Sang‐Ho , McHugh Mark A. 
Published: April 2003

AbstractCloud‐point data to 180°C and 2,800 bar are presented for three poly(ethylene‐co‐methyl acrylate) copolymers [10, 31, and 41 mol % methyl acrylate (MA)] and for polyethylene in ethylene, ethane, propylene, and propane. At low concentrations of MA in the backbone of the copolymer, the saturated hydrocarbons are better solvents for the copolymer than their olefinic analogs because polarizability drives the phase behavior. For the higher MA‐content copolymers, which have more polar repeat units, the unsaturated hydrocarbons are better solvents owing to favorable quadrupolar interactions between the solvent and the polymer segments. The cloud‐point curves of the high MA‐content copolymers in the unsaturated hydrocarbons are shifted to very high temperatures to overcome strong acrylate‐acrylate interactions in the polymer. In fact, the 41 mol % MA copolymer cannot be dissolved in propane at temperatures to 180°C and pressures to 2,800 bar even though the copolymer is predominantly ethylene, while the same copolymer dissolves in propylene at 40°C and at pressures as low as 1,400 bar. Although the Sanchez‐Lacombe equation of state is used to model the cloud‐point curves, two temperature‐dependent mixture parameters are needed for a good fit of the data. © 1992 John Wiley & Sons, Inc.
Structure factor for starburst dendrimers
Authors: Hammouda Boualem 
Published: April 2003

AbstractAdvances in polymer synthesis have made possible the polymerization of “starburst dendrimer” gels which are grown from a central initiator core through controlled branching reactions with a constant multiplication of the number of monomeric blocks from one generation to the next. The structure factor for such dendrimers is calculated using Gaussian monomer‐monomer interactions. The results are somewhat lengthy but analytical forms are obtained. © 1992 John Wiley & Sons, Inc.
Monte Carlo calculations of hole size distributions: Simulation of positron annihilation spectroscopy
Authors: Vleeshouwers S. , Kluin J.‐E. , Mcgervey J. D. , Jamieson A. M. , Simha R. 
Published: April 2003

AbstractConsequences are explored of a hole size distribution in an amorphous polymer for the ortho‐positronium (o‐Ps) lifetime (τ3) and intensity (I3), determined by positron annihilation lifetime spectroscopy. The disordered lattice model, with a vacancy fraction h as a central quantity, is used to represent the equation‐of‐state behavior of the polymer. By means of Monte Carlo simulations, we obtain the cluster size distribution as a function of h and hence temperature. The predicted average cluster size and the cluster concentration are compared to τ3 and I3 data, respectively, for bisphenol‐a polycarbonate. Furthermore, the influence of an o‐Ps lifetime distribution on the experimental mean τ3 is investigated. By mimicking the computational methods used in experimental analysis, agreement between experiment and theory in respect to τ3 and to I3 in the melt ensues. In the glass, however, the experimental I3 becomes increasingly smaller with decreasing temperature than is computed. These deviations may result from a distortion of the equilibrium free volume. © 1992 John Wiley & Sons, Inc.
Regular, adjacent reentry folding in single crystals of a liquid crystal polymer crystallized from the nematic state
Authors: Lin D. , Dean D. , Geil P. H. 
Published: April 2003

AbstractFolded chain single crystals 35 Å thick have been grown from the liquid crystal state of an aromatic‐aliphatic azomethine ether polymer (AZMEP‐n) having a 10‐carbon flexible segment (n = 10). Electron diffraction has permitted refinement of the triclinic unit cell. The molecular axes lie at an ca. 65° angle to the lamella normal and fold every third chemical repeat distance. For AZMEP‐1 and ‐8 extended chain lamellae are formed; for AZMEP‐7 both folded and extended chain lamellae are found. The observations of folded chain lamallae are in agreement with prior suggestions from our laboratory of chain folding in the liquid crystalline state in thin films. © 1992 John Wiley & Sons, Inc.
The application of simultaneous chemiluminescence and thermal analysis for studying the glass transition and oxidative stability of poly(N‐vinyl‐2‐pyrrolidone)
Authors: Scheirs J. , Bigger S. W. , Then E. T. H. , Billingham N. C. 
Published: April 2003

AbstractA computer‐controlled chemiluminescence (CL) instrument incorporating a differential scanning calorimeter was used to simultaneously acquire photochemical and enthalpic data for poly(N‐vinyl‐2‐pyrrolidone) (PVP). Samples were subjected to a linear temperature ramp under nitrogen and their luminescence response recorded. The resultant dynamic CL peak is attributable to the decomposition of hydroperoxide groups and the subsequent mutual termination of secondary polymer peroxyl radicals. It is shown that dynamic CL can be used to characterize the level of oxidation in PVP, which in commercial samples, may be partly related to the level of residual polymerization inititor and to the drying process. The temperature at which maximum CL emission occurs correlates with the glass transition temperature (Tg) of the polymer and increases with increasing molecular weight. A marked increase in the Tg of PVP occurs after it is aged in air for 24 h at 120°C. This is due to the loss of adsorbed moisture from the polymer which was confirmed by thermogravimetric analysis. Oxidation profiles of PVP were obtained by plotting the integrated CL peak area as a function of aging time. The profiles are compared with data obtained from isothermal CL and viscosity measurements. Gas perturbation experiments suggest that when drying PVP under nitrogen at elevated temperatures significant populations of longlived macroalkyl radicals are formed which can peroxidize the polymer on exposure to air. © 1993 John Wiley & Sons, Inc.
Oxygen permeability of surfactant/polymer composite films with multibilayer and inverted hexagonal structure
Authors: Taguchi Kazuhiro , Yano Shoichiro , Hiratani Kazuhisa , Minoura Norihiko 
Published: April 2003

AbstractThe permeability of oxygen through horizontally oriented multibilayer films of polyion complexes prepared from quaternary ammonium‐type surfactants [CH3(CH2)n‐1]2N+(CH3)2Br−(n = 14, 16, 18), and poly(p‐styrenesulfonate) or poly[2‐(acrylamido)‐2‐methyl‐1‐propanesulfonate], was measured in water using an oxygen electrode. The permeability depended mainly on the phase of the multibilayers. Thus, it increased abruptly (about 10‐fold) near each phase transition temperature because of the fluidity enhancement of the multibilayer. Inverted hexagonal type nonbilayer films prepared from the polyion complexes and cholesterol had greater permeability (2–20‐fold) than the multibilayer films in both phases. The large permeability of the nonbilayer films was attributed to the lack of a barrier such as the bilayer and lower crystallinity of the films. It was associated neither with an increase in thermal movement of the lipid surfactant molecules nor with an increase in the water content of the films by the addition of cholesterol. © 1993 John Wiley & Sons, Inc.
Capillary and slit‐die flow of two liquid‐crystalline polymers. The effect of pressure on viscosity
Authors: Izu Pilar , Muñoz María Eugenia , Peña Juan J. , Santamaría Anton 
Published: April 2003

AbstractViscosity measurements on two commercial thermotropic liquid crystalline polymers (LCPs) (a copolyester and a polyesteramide) were performed using both capillary and slit die methods. The results are in agreement with those presented in the literature for the same LCPs, when the measurements are carried out with a L/D = 30 die; these results are affected more by Bagley corrections for the polyesteramide than for the copolyester. For both LCPs, viscosities measured in the slit die are lower than those obtained by capillary rheometry. Nevertheless, the difference is much bigger in the case of the polyesteramide, for which a reduction by a factor of 3 is observed. This is not due to the preshear or thermal history, since the same piston‐barrel system and thermal treatment were applied in both types of measurements. Depending on the polymer sample and temperature, concave and convex curvatures were observed in the pressure profiles during the slit flow. From these curvatures, the pressure coefficient α of viscosity was evaluated. However, in the case of the polyesteramide the convex curvature leads to a negative coefficient (the viscosity decreases with pressure, instead of increasing). This result may be explained by envisaging a change in the structure of the melt along the slit length. © 1993 John Wiley & Sons, Inc.
Protonation of leucoemeraldine in the solid state and in solution
Authors: Neoh K. G. , Kang E. T. , Tan K. L. 
Published: April 2003

AbstractThe protonation of leucoemeraldine in power form and in N‐methylpyrrolidinone (NMP) solution by HCIO4 and HBF4 has been studied by x‐ray photoelectron spectroscopy (XPS), infrared (IR), and ultraviolet (UV)‐visible absorption spectroscopy. In powder form, less than 25% of the amine nitrogens can be protonated in the absence of oxygen. The effects of oxygen on the degree of protonation and the distribution of amine and imine units upon deprotonation of the salt are investigated. The degree of protonation in leuccemeraldine can be increased to about 50% with 3 M HCIO4, similar to that achievable with emeraldine base in powder form. In NMP solution, leucoemeraldine is easily oxidized by dissolved oxygen. Protonation of both leucoemeraldine and emeraldine base in NMP solutions results in metastable species which gradually undergo deprotonation. The resulting products are affected by the O2 content of the solutions. © 1993 John Wiley & Sons, Inc.
Gas transport in polybutadiene treated with aqueous bromine
Authors: Rein D. H. , Baddour R. F. , Cohen R. E. 
Published: April 2003

AbstractDiffusion, solubility, and permebility coefficients were measured for He, Co2, Ar, and CH4 in polybutadiene (PB) and in polybutadiene reacted in the solid state to various extents with aqueous bromine. Analysis of the sorption curves and X‐ray emission spectra showed that the bromination created a heterogeneous membrane with an outer brominated skin and an unreacted core. At relatively low extent of bromination, the diffusion and permeability coefficients for CO2, Ar, and CH4 decreased by two orders of magnitude, while the transport coefficients for He were virtually unchanged. The permeability coefficients for CO2, Ar, and CH4 became immeasurably small after about 3% bromination. The ideal separation factor for gas pairs with different molecular size increased with bromination, suggesting applications in gas separation processes. © 1993 John Wiley & Sons, Inc.
Cosolvency effects on copolymer solutions at high pressure
Authors: Hasch Bruce M. , Meilchen Melchior A. , Lee Sang‐Ho , Mchugh Mark A. 
Published: April 2003

AbstractCloud‐point data to 180°C and 2800 bar are presented for polyethylene, poly(methyl acrylate), and two poly(ethylene‐co‐methyl acrylate) copolymers (10 and 31 mol % methyl acrylate) in propane and chlorodifluoromethane with two cosolvents, acetone and ethanol. The addition of small amounts of either cosolvent to the copolymer–solvent mixtures shifts the cloud‐point curve to lower pressures and temperatures, as both cosolvents provide favorable polar interactions with the acrylate group in the backbone of the copolymer. Ethanol has a larger effect than acetone since ethanol hydrogen bonds to the acrylate group. However, if the concentration of ethanol is increased above ca. 10 wt %, it self‐associates and reverts to antisolvent behavior, forcing the copolymer out of solution. For nonpolar polyethylene–propane mixtures, the polar cosolvents behave as traditional an‐tisolvents. In poly(methyl acrylate)–chlorodifluoromethane mixtures, both polar cosolvents enlarge the single‐phase region. The cloud‐point curves for the (co)polymer–propane–acetone mixtures are modeled reasonably well using the Sanchez–Lacombe equation of state with two adjustable mixture parameters. No attempt is made to model the mixtures that exhibit hydrogen bonding. © 1993 John Wiley & Sons, Inc.
Kinetics of phase separation in polymer blends. Calculations based on nonlinear theory
Authors: Wang Zheng‐Yu , Konno Mikio , Saito Shozaburo 
Published: April 2003

AbstractSuzuki's scaling theory for transient phenomena is applied to the calculation of the kinetics of phase separation in the early‐to‐intermediate stage based on a nonlinear theory proposed by Langer, Bar‐on, and Miller (LBM). Calculated results are compared with experimental data on light scattering from a polymer blend system. Deviations from predictions of Cahn's linearized theory in the early time range of phase separation can be explained well by the proposed method of calculation. Nonlinear effects are found to play an essential role in characterizing the light scattering behavior of phase separation in the intermediate stage. Time evolutions of the single‐point distribution function of composition are calculated, and the results are in good agreement with those reported in digital imaging analysis experiments and computer simulations of the time‐dependent Ginzburg‐Landau equation. The influence of asymmetry of free‐energy on the single‐point distribution function is also investigated in this study. © 1993 John Wiley & Sons, Inc.
Optical analysis of dichroism measurements in polymer science
Authors: Wold Erik , Bremer Johannes , Hunderi Ola 
Published: April 2003

AbstractThe polarization properties of an optical system, source–interferometer–polarizer–polymer film–detector, have been calculated. Using Mueller matrices, the intensity has been obtained as a function of polarizer angle. It is shown in some detail how polarization of the beam in both interferometer and detector optics distort the spectra. The contributions from the finite extinction ratio of the polarizer are also calculated and intensity variations caused by beam‐wandering are discussed. It is shown that the commonly used procedure for correcting the spectra is wrong. Better methods for correcting the spectra are proposed. The influence of a uniaxial refractive index on the data is discussed, and experimental methods that can deal with refraction effects are presented. © 1993 John Wiley & Sons, Inc.
Toughening of epoxies via craze‐like damage
Authors: Sue H.‐J. , Garcia‐Meitin E. I. , Orchard N. A. 
Published: April 2003

AbstractThe fracture behavior of a core‐shell rubber (CSR) modified epoxy is investigated using both fracture mechanics and microscopy tools. The CSR‐modified epoxy is found to be toughened via numerous line‐array cavitations of the CSR particles, followed by plastic flow of the epoxy matrix. The toughening effect via the above craze‐like damage process is found to be as effective as that of the well‐known widespread rubber cavitation/matrix shear yielding mechanisms. The conditions for triggering the craze‐like damage appear to be both stress state and rubber concentration dependent. The type of rubber tougheners utilized also plays a critical role in triggering this rather unusual craze‐like damage in epoxy systems. © 1993 John Wiley & Sons, Inc.
The effect of amorphous orientation on the oxygen permeability of polypropylene films
Authors: Taraiya A. K. , Orchard G. A. J. , Ward I. M. 
Published: April 2003

AbstractOxygen permeability measurements have been made on uniaxially and biaxially oriented polypropylene samples. X‐ray diffraction pole‐figure measurements provided the crystalline orientation functions. These results combined with density and refractive index measurements provided the amorphous orientation functions based on the two‐phase model. A good correlation has been found between the amorphous orientation and the oxygen permeability of the samples. © 1993 John Wiley & Sons, Inc.
High‐resolution solid‐state 13C NMR study of ethylcellulose films
Authors: Kimura Tsunehisa , Azuma Jun‐Ichi , Gray Derek G. 
Published: April 2003

AbstractEthylcellulose films cast from concentrated solutions of chloroform, benzene, and carbon tetrachloride were subjected to the NMR relaxation measurements including 1H spin‐lattice relaxation time (T1H), rotating‐frame 1H spin‐lattice relaxation time (T1ρH), and 13C spin‐lattice relaxation time (T1C). The values of T1ρH for carbons in the glucose units of ethyl‐cellulose were of the same order of magnitude as those reported for the crystalline and noncrystalline regions of ramie cellulose. The values of T1C for unsubstituted C2, C3 carbons were smaller than those for the corresponding carbons in the noncrystalline region of native celluloses. The T1C values for unsubstituted C2, C3, and substituted C6 carbons showed a small but definite dependence on the solvent from which the films were cast. © 1993 John Wiley & Sons, Inc.
The dependence of slow crack growth in a linear polyethylene on test temperature and morphology
Authors: Lu Xici , Mcghie Andrew , Brown Norman 
Published: April 2003

AbstractThe slow crack growth behavior of a linear polyethylene with different morphologies was studied by using three point bending with a single edge notched specimen at testing tem‐peratures from 30 to 80°C. The morphology was varied by annealing the quenched material at temperatures from 86°C to 135°C. It was found that at test temperatures of 60°C or less, the changes in failure time with annealing temperature are very similar to the change in density with a maximum at 130°C. At testing temperatures above 60°C, the relationship of between failure time and annealing temperature is altered when the test is in the range of the α transition temperature. These results indicate that with respect to slow crack growth in the case of a homopolymer the strength of the crystals is relatively more important than the number of tie molecules. © 1993 John Wiley & Sons, Inc.
Miscible blends of modified poly(aryl ether ketones) with aromatic polyimides
Authors: Karcha Robert J. , Porter Roger S. 
Published: April 2003

AbstractThe phase behavior of binary blends of poly(ether ether ketone) (PEEK), sulfonated PEEK, and sulfamidated PEEK with aromatic polyimides is reported. PEEK was determined to be immiscible with a poly(amide imide) (TORLON 4000T). Blends of sulfonated and sulfamidated PEEK with this poly(amide imide), however, are reported here to be miscible in all proportions. Blends of sulfonated PEEK and a poly(ether imide) (ULTEM 1000) are also reported to be miscible. Spectroscopic investigations of the intermolecular interactions suggest that formation of electron donoracceptor complexes between the sulfonated/sulfamidated phenylene rings of the PEEKs and the n‐phenylene units of the polyimides are responsible for this miscibility. © 1993 John Wiley & Sons, Inc.
On the measurement of structural relaxation in polymers using positron annihilation lifetime spectroscopy
Authors: Li Xue Song , Boyce Mary C. 
Published: April 2003

AbstractPositron annihilation lifetime spectroscopy has been identified as an effective means of characterizing the free volume content of amorphous polymers. The lifetime and intensity of the ortho‐positronium (o‐Ps) pick‐off annihilation has been found to correlate with the average size and density of free volume sites, respectively. Recently, PALS has been used to evaluate and monitor the physical aging and structural relaxation of polymers in terms of both initial state and evolution in state with time. However, during extended PALS measurements in insulating materials, an electric field can build up due to positron‐electron annihilation and can effectively reduce the probability of positronium formation. In this paper, an observed decrease in intensity associated with the o‐Ps annihilation component in the glassy polymers polycarbonate and polystyrene is found to be unrelated to structural relaxation of the materials over the time periods examined as reported earlier by others, and, instead, to be more likely a result of electric charge build‐up. © 1993 John Wiley & Sons, Inc.
Gas transport through homogeneous and asymmetric polyethersulfone membranes
Authors: Kumazawa H. , Wang J.‐S. , Sada E. 
Published: April 2003

AbstractBoth homogeneous and asymmetric polyethersulfone (PES) membranes were prepared by solvent casting. The sorption and permeation behavior of CO2, O2, and N2 using these two kinds of cast PES membranes and commercially available homogeneous PES film was investigated to extract the pressure dependence of gas permeability and the permselectivity for CO2 relative to N2, and to confirm the validity of the working assumption that a skin layer in an asymmetric membrane can be essentially replaced by a thick homogeneous dense membrane. The pressure dependence of the mean permeability coefficient to CO2 in homogeneous membranes obeys the dual‐mode mobility model. The ideal separation factor for CO2 relative to N2 at an upstream pressure of 0.5 MPa attains ca. 40, while the permeability to CO2 is about 2.7 Barrer at the same upstream pressure. The same separation factor in asymmetric membranes amounts to 35. The diffusion behavior for the skin layer in an asymmetric membrane with a thin skin layer can be simulated approximately by that in a homogeneous dense membrane. © 1993 John Wiley & Sons, Inc.
Melt spinning and mechanical properties of semirigid liquid‐crystal copolyesters
Authors: La Mantia F. P. , Valenza A. , Città V. , Pedretti U. , Roggero A. 
Published: April 2003

AbstractMelt‐spinning and mechanical properties of fibers of a new class of semirigid thermotropic liquid‐crystal polymers are presented. These copolyesters are synthesized from 4‐4′‐dihydroxybiphenyl (B), 4‐hydroxybenzoic acid (H), and flexible units provided by aliphatic diacids. The flexible units depress the melting temperature without strongly depressing the mechanical properties. These liquid‐crystal polymers can be easily spun at high draw ratios. Indeed, unlike rigid liquid‐crystal polymers, relatively high draw ratios are needed to attain high mechanical strength. Tensile moduli of about 28 GPa and tensile strengths of about 350 MPa are obtained. © 1993 John Wiley & Sons, Inc.
Influence of the sulfonate countercation on the thermal stability of nafion perfluorosulfonate membranes
Authors: Feldheim Daniel L. , Lawson Del R. , Martin Charles R. 
Published: April 2003

AbstractWe report a strong dependence of the thermal stability of Nafion® perfluorosulfonate ionomer on the nature of the counterion associated with the fixed sulfonate site. These results were obtained using thermal gravimetric analysis on a series of alkali metal and alkyl ammonium cation‐exchanged Nafion films. We have found that the temperature of decomposition of Nafion is inversely dependent on the size of the exchanged cation; i.e., Nafion films show improved thermal stability as the size of the counter cation decreases. We attribute this inverse relationship of thermal stability with counterion size to an initial decomposition reaction which is strongly influenced by the strength of the sulfonate‐coun‐terion interaction. © 1993 John Wiley & Sons, Inc.