bluuebunny/crossref_metadata_2025_split huggingface dataset:
Random homogeneous sodium sulfonate polysulfone ionomers: Preparation, characterization, and blend studies
Authors: O'Gara John F. , Williams David J. , Macknight William J. , Karasz Frank E. 
Published: April 2003

AbstractThe sodium salts of randomly sulfonated polysulfone (Na‐SPSF), derived from 1,1′‐sulfonylbis‐[4‐chlorobenzene] with 4,4′‐(1‐methylethylidene)‐bis‐[phenol], were prepared over the composition range of 3–30 mol% sodium sulfonate, using improved procedures in which the sulfonating complex was introduced into an intensely agitated polymer solution. In contrast to earlier work, Tg was found to increase nonlinearly with sodium sulfonate content. A SAXS study provided no evidence of ionic clustering in these polymers. Binary blends of Na‐SPSFs differing only in composition were prepared by casting films from solution, and their phase behavior was studied by dynamic mechanical analysis after annealing at 250°C. It was found that the blends were miscible up to a composition difference of about 9–10 mol% sodium sulfonate. Using this fact it was possible to calculate a value for χABn of 200–250, where χAB represents the segmental interaction parameter between unmodified and modified repeat units, and n is the degree of polymerization. Uncertainty in the degree of ionic association places a degree of uncertainty on the effective value of n and therefore on χAB. The product, however, is independent of any assumptions regarding molecular associations.
Effect of doping on thermoluminescence in polymers. II. Polycarbonate doped with triphenyl methane and xanthene dyes
Authors: Vanderschueren J. , Linkens A. , Niezette J. 
Published: April 2003

AbstractThe thermoluminescence (TL) of polycarbonate doped with triphenyl methane and xanthene dyes was measured following irradiation with ultraviolet light at 77 K and the effect exercised by systematically varying excitation wavelength, irradiation dose, and dopant concentration were investigated. The TL glow curves are characterized by two distinct peaks that can be attributed to genuine emissions of the dopant‐polymer systems and involve continuous distributions of apparent activation energies as determined by partial heating techniques. The low‐temperature peak extends over the temperature interval corresponding approximately to the complex β relaxation of the polymeric units (short‐range chain motions), but no obvious correlation between the two phenomena can be evidenced because the TL peak is never structured and the values and type of evolution of apparent activation energies as a function of temperature are clearly different from those observed for the β relaxation. In this temperature range the TL properties are consistent with an ionization of the dye followed by a recombination process involving electron tunneling from trap to luminescence center rather than thermal excitation. The second TL peak appears in a unusually high temperature region (> 250 K) where no intrinsic relaxation of the polymeric matrix is known to occur. This is not to say that the chain motions cannot contribute to some extent to the detrapping processes. Generally speaking, however, the TL results show that interpreting glow curves only in terms of relaxation processes should be done with great caution and that in certain cases an observed emission must be considered as specific to the dopant‐polymer system rather than to the polymer itself.
Thermal expansion of irradiated polytetrafluoroethylene
Authors: Subrahmanyam H. N. , Subramanyam S. V. 
Published: April 2003

AbstractThe thermal expansion coefficient of gamma‐irradiated Polytetrafluoroethylene (PTFE) has been measured in the temperature range 80–340 K by using a three‐terminal capacitance technique. The samples are irradiated in air at room temperature with gamma rays from a Co60 source at a dose rate of 0.26 Mrad/h. The change in crystallinity is measured by an x‐ray technique. The expansion coefficient is found to increase with radiation dose below 140 K owing to the predominant effect of degradation. Above 140 K, the expansion coefficient is found to decrease with radiation dose because of the enhanced crystallinity. The temperatures of the two first‐order phase transitions are also found to shift to lower temperatures owing to degradation of PTFE.
Styrene‐terminated polysulfone reactive oligomers: Cure and properties
Authors: Garcia Dana 
Published: April 2003

AbstractOligomers end‐capped by groups capable of thermally induced polymerization have found wide applications in advanced structural composites and adhesives. The styrene‐terminated polysulfone reactive oligomers described in this paper represent an example of such thermosetting systems. The advantage of these compounds, over high molecular weight polysulfone resin, lies in their easier processing and improved solvent resistance. This paper addresses the properties of the neat oligomer as a function of initial molecular weight and those of the resulting cured resin as well as a complete characterization of the curing reaction. Furthermore, a comparison will be made between these oligomers and the better known acetylene‐terminated sulfone oligomers.
Calorimetric study of blends of poly(butylene terephthalate) and a liquid crystalline polyester
Authors: Paci Massimo , Barone Corrado , Magagnini Pier Luigi 
Published: April 2003

AbstractThe thermal properties of solution‐prepared blends of poly(butylene terephthalate) (PBT) and liquid crystalline poly(biphenyl‐4,4′‐ylene sebacate) (PB8) have been studied by differential scanning calorimetry (DSC). The smectic‐to‐isotropic (s → i) transition of the mesomorphic component is observed at temperatures slightly increasing with the PB8 content, in the 270–280°C range; on cooling, the mesophase formation (i → s transition) takes place at temperatures that decrease markedly with decreasing PB8 content. The temperatures of the crystal‐to‐smectic and smectic‐to‐crystal transitions of PB8 are almost invariant with blend composition. The melting and crystallization temperatures of the PBT phase decrease on increasing the content of the liquid crystalline component.These results, together with those of isothermal calorimetry of both the crystallization of the PBT component and the mesophase formation of the PB8 component of the blends, indicate that the two polymers are not immiscible in the isotropic state. In this latter state, however, the two polyesters undergo transesterification, which can be followed through changes in the DSC scans. The effect of the thermal history on the properties of the blends has been studied with particular attention. Both the dynamic and the isothermal calorimetric measurements provide evidence of an increase of the degree of crystallinity of PBT on addition of the liquid crystalline component up to about 35–50% by weight.
Morphological partitioning of chain ends and methyl branches in melt‐crystallized polyethylene by 13C‐NMR
Authors: Pérez E. , Vanderhart D. L. 
Published: April 2003

AbstractThe partitioning of methyl and vinyl ends between the crystalline and noncrystalline regions of polyethylene has been investigated using 13C‐NMR in the solid state. The polyethylene samples, which were crystallized from the melt, varied in molecular weight, polydispersity, crystallization rate, and comonomer content. For the limited set of samples considered, the ratio of crystal to overall end concentration is independent of those variables. This ratio takes the values of 0.75 and 0.60 for the methyl and vinyl ends, respectively. When the crystalline fraction of these samples is taken into account, 50–75% of the total saturated ends and 42–63% of the total vinyls reside in the crystal. For an ethylene/propylene copolymer, 21–27% of the methyl branches were determined to be in the crystal. This level of incorporation puts methyl branches in a position intermediate between chain ends and ethyl branches.
Mechanical and dielectric relaxations of epoxide resins containing the spiro‐ring structure. II. Effect of the introduction of methoxy branches on low‐temperature relaxations of epoxide resins
Authors: Ochi Mitsukazu , Yoshizumi Makoto , Shimbo Masaki 
Published: April 2003

AbstractMechanisms for low‐temperature relaxations of three spiro‐ring‐type epoxide resin systems with and without methoxy branches were investigated by comparison with those of a bisphenol A‐type resin system. In the spiro‐ring‐type epoxide resin systems, two well‐defined relaxation peaks, denoted as the β and β′ relaxations, and a shoulder peak were observed at about −70, +60, and 0°C, respectively. The magnitude of the β relaxation was decreased by the introduction of methoxy branches on the phenylene group. This phenomenon could be interpreted as a result of the formation of hydrogen bonds between the hydroxy‐ether group and methoxy branch. Moreover, it was concluded that the β′ relaxation and the shoulder peak are due to the motion of the p‐phenylene group adjacent to the spiro‐ring and of the hydroxy‐ether group blocked by the hydrogen bond, respectively.
WAXS studies on block copolymers of ethylene and propylene
Authors: Mo Zhishen , Wang Lixiao , Zhang Hongfang , Han Ping , Huang Baotong 
Published: April 2003

AbstractWide‐angle X‐ray scattering from presumed block copolymers of polypropylene (PP) and ethylene‐propylene copolymer (EPR), i.e., PP‐EPR and PP‐EPR‐PP, synthesized by sequential polymerization with δ‐TiCl3Et2AlCl, was examined and compared with WAXS of mechanical blends and chain‐transfer mixtures of PP and EPR with comparable compositions. The peak at 2θ = 20° for both the copolymers and the mixtures was attributed to the γ modification of PP in EPR. A strong variation in the ratio of diffraction intensities I040/I110 of PP in block copolymers and mixtures was explained in terms of crystallite growth in different directions. Analysis of the patterns and calculation of crystallinity, crystallite size, and lattice parameters led to the conclusion that block structure existed in the prepared copolymers.
Dynamics of a single copolymer chain
Authors: Benmouna M. , Duval M. , Borsali R. 
Published: April 2003

AbstractThe dynamics of a single copolymer chain in a solution containing identical chains is studied. The intermediate scattering function is calculated, and two different modes are identified and analyzed as a function of wave vector q. The first mode is characteristic of the copolymer system and leads to a peculiar constant relaxation frequency as q goes to zero. The second mode represents the diffusion of the chain in the solution.
Kinetics of mesophase formation and crystallization in poly(diethylsiloxane)
Authors: Papkov V. S. , Svistunov V. S. , Godovsky Yu. K. , Zhdanov A. A. 
Published: April 2003

AbstractOptical and calorimetric studies of the kinetics of mesophase formation and crystallization in poly(diethylsiloxane) have been conducted. The mesomorphic phase is found to grow from the isotropic melt in the form of lamellar domains about 2 μm thick in the temperature range 293–307 K. According to birefringence data, macromolecules in the mesomorphic lamellae are perpendicular to the end faces. The kinetics of mesophase formation obey the Avrami equation with the morphological parameter n close to 2 (it is equal to 1.75 ± 0.05), which corresponds to the two‐dimensional growth of the mesomorphic phase from athermal nuclei. The limiting conversion of the isotropic melt was shown to be temperature‐dependent. This is likely to be connected with a change in the number of nuclei with temperature. The crystallization of polymer from the mesomorphic state occurs with retention of the optical texture of the sample. The process proceeds not as a sporadic crystallization of individual mesomorphic lamellae but as a growth of the nucleated crystalline regions via a consecutive incorporation of adjacent crystallizing lamellae.
Surface‐enhanced raman scattering from poly(4‐vinyl pyridine)
Authors: Roth P. G. , Boerio F. J. 
Published: April 2003

AbstractSurface‐enhanced Raman scattering (SERS) has been observed for poly(4‐vinyl pyridine) absorbed onto silver island films. Bands near 1219 and 1613 cm−1, which are weak in normal Raman spectra of PVP, are strong in SERS spectra, and the band near 1020 cm−1, which is the strongest band in the normal spectra, is relatively weak in SERS. The strongest bands in the SERS spectra all belong to the same symmetry species as αZZ, implying that the pyridine moieties are adsorbed through the nitrogen atoms with a vertical conformation. The ring breathing mode of the pyridine rings is observed near 1020 cm−1, a frequency characteristic of pyridinium ions or coordinated pyridine, providing further evidence for adsorption through the nitrogen atoms. Silver catalyzed photooxidation, which can lead to the appearance of artifacts in SERS spectra, particularly of polymers, can be reduced by overcoating SERS samples with thin films of polymers such as poly(methyl methacrylate) that have low Raman scattering cross sections.
Prediction of the glass transition temperature of polymers: A model based on the principle of corresponding states
Authors: DiBenedetto A. T. 
Published: April 2003

AbstractThe application of corresponding state principles to describe the properties of polymers is implicit in many of the fundamental studies of polymeric behavior. The seminal works of Prigogine, Hildebrand, Eyring, Flory, Gibbs, and DiMarzio in which multidimensional lattice representations and refined statistical mechanical approaches have been used are the basis for much of today's understanding of the thermodynamic behavior of polymers and their solutions. In this work the lattice energy of a polymer is defined in terms of reduced molecular parameters, and it is assumed that all polymers with the same functional form for their lattice energies will be in corresponding states. A reduced second order transition temperature is defined relative to a characteristic temperature T* = sϵ*/2kv* c, where the molecular parameters refer to the properties of the repeating segments of the polymer chain. Equations are derived that express the effects of molecular weight, plasticization, degree of crosslinking, and copolymerization on the second order (i.e., glass) transition temperature. In their limits, the equations are shown to reduce in form to equations derivable from free volume theory. They are also used to analyze successfully a variety of glass transition temperature data available in the literature on homogeneous uncrosslinked and crosslinked polymers, plasticized polymers, and random copolymers.
Depression of the glass transition temperature of poly(methyl methacrylate) by plasticizers: Conformity with free volume theory
Authors: Kalachandra S. , Turner D. T. 
Published: April 2003

AbstractMixtures of poly(methyl methacrylate) (PMMA) and plasticizer were made by γ‐irradiation of mixtures of methyl methacrylate with diethyl phthalate or with dioctyl phthalate. The glass transition temperature Tg was determined by differential scanning calorimetry. Plots of Tg versus volume fraction of PMMA were found to conform to the simple free volume theory of Kelley and Bueche, using physical property values either reported in the literature or else calculated by Bondi's procedures.
The effect of network chain‐length distribution, specifically bimodality, on strain‐induced crystallization
Authors: Sun C.‐C. , Mark J. E. 
Published: April 2003

AbstractPolyurethane elastomers were prepared from a series of poly(ethylene oxide) samples by end‐linking the chains into “model” trifunctional networks. The molecular weight Mc between crosslinks in such networks is simply the number‐average molecular weight Mn of the precursor polymer. End‐linking samples separately gave networks with unimodal distributions of network chain lengths, whereas end‐linking mixtures of two samples having very different values of Mn gave bimodal distributions with average values of Mc equal to the average value of Mn for the two samples. Stress‐strain isotherms in elongation were obtained for these networks, both unswollen and swollen to various extents. Strain‐induced crystallization was manifested in elastic properties that changed significantly with changes in temperature. Swelling has more complicated effects, since it causes deformation of the network chains as well as melting of some of the crystallites. Comparisons among stress‐strain isotherms at constant Mc indicate that bimodality facilitates strain‐induced crystallization.
Counterion and solvent effects on the dilute solution viscosity of polystyrene ionomers
Authors: Agarwal Pawan K. , Garner Richard T. , Graessley William W. 
Published: April 2003

AbstractWe present an analysis of data on the intrinsic viscosity [η] of sulfo‐polystyrene ionomers in several solvents for a variety of sulfonation levels and counterions. For solvents of low dielectric constant, 2 < ε < 18, [η] decreases from the base polymer value [η]0 with increasing substitution level. This behavior was attributed to intramolecular association of ionic dipoles. The ratio [η]/[η]0 was found to depend on a single reduced variable αAαSx, where x is the fractional substitution, αA depends only on the counterion, and αS ∝ ε−1 depends only on the solvent. For solvents of high dielectric constant, 36 < ε < 47, [η] increases approximately as x3, and counterion effects are small. This behavior was attributed to ionic dissociation, giving rise to a polyelectrolyte effect. Implications of the low ε results are discussed in relation to association‐induced gelation behavior and possible generalizations of the reduced variables approach.
Hole transport of trans‐1,2‐biscarbazolylcyclobutane‐doped poly(bisphenol A carbonate) film
Authors: Tsutsumi Naoto , Yamamoto Masahide , Nishijima Yasunori 
Published: April 2003

AbstractThe hole transport of trans‐1,2‐biscarbazolylcyclobutane (CB) doped poly(bisphenol A carbonate) (PC) film has been investigated in the CB concentration range of 3.8 × 10−4 mol cm−3 (12 wt%) to 1.6 × 10−3 mol cm−3 (51 wt%). The hole mobility increased drastically with increasing CB concentration. The hole mobility was analyzed by a random hopping model. The localization radius ρ0 of the CB/PC system was 1.9 Å, which is larger than that obtained for the N‐isopropyl‐carbazole‐doped PC system. This suggests that the larger localization radius of the CB/PC system is related to the larger spatial extent of the CB molecule. The highest hole mobility of 2.9 × 10−6 cm2 V−1 s−1 was obtained when the CB concentration was 1.6 × 10−3 mol cm−3 (51 wt%) at E = 1.6 × 105 V cm−1 and T = 298 K. This mobility is about 10 times higher than that of poly(N‐vinylcarbazole) (PVCz). The activation energy of hole mobility for the CB/PC system decreased with increasing CB concentration and was 0.31 eV at 51 wt% of CB, which is lower than the 0.45 eV for PVCz. The low activation energy for the CB/PC system is ascribed to the absence of an excimer‐forming site that works as a multiple‐trapping site for hole carriers.
Angular dependence of 1H‐ and 2H‐NMR spectra of H2O and D2O absorbed in cellulose acetate film
Authors: Matsumura Kazunori , Hayamizu Kikuko , Nakane Takashi , Yanagishita Hiroshi , Yamamoto Osamu 
Published: April 2003

Abstract1H‐ and 2H‐NMR spectra of H2O and D2O absorbed in cellulose acetate films were observed while changing the angle between the plane of the film and the magnetic field. 1H‐NMR spectra show dipolar splittings that vary depending on the angle. The splitting has a maximum when the surface of the film is perpendicular to the magnetic field. From the angular dependence of the dipolar splitting, it is recognized that the proton‐proton dipolar axis of water molecules tends to orient perpendicularly to the surface of the film. 2H‐NMR spectra that show quadrupolar splittings also indicate that the quadrupolar axis tends to orient perpendicularly to the film. The so‐called bound water and free water in the film can exchange rapidly on the NMR time scale, so that the line width and the splitting of the NMR spectra become smaller as the amount of water in the film increases. From the temperature dependence of line widths, the apparent reorientational activation energy of water molecules in the film is estimated to be 25 kJ/mol from 1H‐NMR and 31 kJ/mol from 2H‐NMR.
Influence of chemical structure on nonelastic mechanical properties in polystyryl‐pyridine resins
Authors: Caux X. , Coulon G. , Escaig B. 
Published: April 2003

AbstractWe propose a micromechanical characterization of the chemical structure (i.e., the state of cure) of polystyryl‐pyridine (PSP) resin. The nonelastic work‐hardening rate K is measured in the preyield stage during compression tests at constant strain rate. The nonelastic deformation is analyzed from a metallurgical point of view; the parameter K varies as the inverse of the nucleation rate for dislocations and thus is a measure of the ability of the material to deform plastically. The comparison with high‐resolution solid‐state carbon‐13 NMR experiments shows that, at room temperature, the ability of PSP resin to deform plastically depends mainly on the degree of crosslinking, whatever the length of prepolymer molecule; however, at high temperatures (T = 200°C) it is affected by the length of prepolymer molecule during curing, whatever the degree of crosslinking. Plastic deformation of PSP resin is easier at 200°C than at room temperature. The longer the duration of curing, the better the mechanical properties at high temperatures; PSP resin readily deforms plastically and has a sufficiently high elastic modulus.
Mössbauer spectroscopy of Fe2+‐complexed poly(N‐propylpyrrole‐sulfonate)
Authors: Auric P. , Bidan G. 
Published: April 2003

AbstractThe polymer obtained by chemical oxidation of N‐propylpyrrole‐sulfonate (PPS) with Fe(ClO4)3 is studied through elemental analysis and Mössbauer spectroscopy. From elemental analysis data this polymer appears to be composed of a polypyrrolic backbone with side chains of alkylsulfonate pendant groups. These sulfonate groups are mainly in the form of iron salts that act as a dopant of the poly(PPS). Mössbauer spectra of iron‐complexed poly(PPS) has been analyzed as functions of temperature, water content, and applied magnetic field in order to characterize the iron environment. Nearly 95% of the iron ions are ferrous ions in different environments. The spectra of a dried sample or a fully hydrated one, which are recorded at a given temperature, were fitted by using identical isomer‐shift values but two different distributions or quadrupole doublets (the Q.S. evolution with temperature was the same). The Debye temperature of the two samples has the same value, but the recoil‐free fraction falls to zero somewhere above 340 K for a dried sample and near 290 K for the fully hydrated material. These results suggest that the additional water molecules that act as a solvate layer mainly change the lattice properties and that the Fe2+ ions are probably linked to the SO‐terminated side chains of the backbone. These high‐spin Fe2+ ions are in the fast relaxation limit at 4 K without external field and have anisotropic magnetic properties under high applied fields. No clusters or dimers have been detected.
FTIR studies of PMR‐15 polyimides
Authors: Garcia Dana , Serafini Tito T. 
Published: April 2003

AbstractFourier‐transform infrared spectroscopy (FTIR) shows that during the curing of PMR‐15 polyimide, formation of an anhydride intermediate occurs prior to the formation of polyamic acid, suggesting that its origin is the diester diacid starting material, as has recently been proposed by Johnston and coworkers. These results disagree with some previous literature reports that have attributed formation of the anhydride to a degradation pathway of polyamic acid and confirm the validity of a recently published paper by Johnston and coworkers.