bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dynamic mechanical relaxations of polyterephthalates based on trimethylene glycols
Authors: Carlos González César , Pereña José Manuel , Bello Antonio 
Published: April 2003

AbstractThe dynamic mechanical relaxations of poly(trimethylene glycol terephthalate) (PTMT), poly(ditrimethylene glycol terephthalate) (PDTMT) and two copolymers obtained from them have been studied between − 150 and 200°C with a dynamic viscoelastometer. The four polymers show three relaxations that are designated α, β, and γ in order of decreasing temperature. The α relaxation is considered to be the glass transition of the polymers. The β relaxation is wider and weaker than the α, as normally occurs in the polyester series. The γ relaxation takes place at temperatures below − 100°C and is usually overlapped by the β relaxation. The influence of thermal and mechanical histories on the nature, location, and intensity of the three relaxations is studied and discussed.
A dielectric study of poly(ethylene‐co‐vinyl acetate)‐poly(vinyl chloride) blends. III. Direct current conductivity and electrode polarization
Authors: Rellick G. S. , Runt J. 
Published: April 2003

AbstractThe large direct current (d.c.) conductance observed at low frequencies and high temperatures in conjunction with a simple electrical circuit model was used to calculate specific conductivities in PVC and mixtures of PVC with a poly(ethylene‐vinyl acetate) copolymer. Activation energies for d.c. conduction and dipole relaxation in PVC and the blends were found to be in reasonable correspondence. The effects of different electrode materials on the d.c. conductance as well as on electrode polarization are discussed.
High‐energy ion implantation of polymers: Poly(vinylidene fluoride)
Authors: Said M. A. , Balik C. M. , Carlson J. D. 
Published: April 2003

AbstractPoly(vinylidene fluoride) films were implanted with high‐energy (up to 6 MeV) He, C, O, and Ni ions and characterized using DSC, FTIR, and solubility measurements. None of the ions were energetic enough to penetrate the polymer film completely. The effects of ion energy, fluence, and ion type were studied individually. The implantation process lowered the crystallinity, induced crosslinking, and produced carbonyl groups on the polymer. The ion energy (in the range 0.4–4.5 MeV for He ions) had the most drastic effect, the radiation damage was found to increase with decreasing energy. The sample implanted with 0.4 MeV He ions lost 81% of its initial crystallinity and was only 24% soluble, even though the incident ions have a range of only 2.7 μm in this case. The other samples retained most of their initial crystallinity but still were substantially cross‐linked. The results can be qualitatively explained by assuming that hydrogen free radicals, produced during implantation, can diffuse throughout the sample and react, resulting in crystallinity and solubility losses beyond the ion deceleration region.
Effect of heating and aging on microstructure of polyester‐polyamide copolymer
Authors: Lefelar J. A. 
Published: April 2003

AbstractPolyester‐polyamide (PET/PA) copolymers offer a wide range of possible applications where both dimensional stability and good impact resistance can be achieved from their synergism. In order to ensure these properties for long‐term use, however, problems of phase separation, volume change, and chemical reequilibration on heating or aging must be identified and overcome. Wide‐angle x‐ray diffraction (WAXD), small‐angle x‐ray scattering (SAXS), and thermal analysis were employed to follow the microstructure of a 70:30 PET/PA copolymer with several different processing histories as a function of heat history and both short‐term and long‐term aging. Heating the copolymer, as received, above the melting temperature of PET caused phase mixing. The effect of heating on crystallinity depended on starting crystallinity. Holding the copolymer at 50°C, just below the glass transition temperature of PET, caused phase separation in samples which had been annealed for 30 min at 150°C. On long‐term aging samples gave evidence of phase mixing. The results indicate highly nonequilibrium structure in the material, regardless of the original processing.
Synthesis and properties of poly(1,2–8,9‐trans‐quinacridono)
Authors: Ruan J. Z. , Litt M. H. 
Published: April 2003

AbstractThe aromatic ladder polymer, poly(1,2–8,9‐trans‐quinacridono) (PQ) has been synthesized. The intermediate polymer was also characterized. Electron paramagnetic resonance (EPR) and conductivity measurements were made on PQ. PQ packs in nematic liquid crystal form. Iodine intercalates and destroys the order during doping, while raising its conductivity by five orders of magnitude.
Polymerization in submonolayers of styrene monomer adsorbed from its vapor phase
Authors: Behbahani Houshang F. , Inoue H. 
Published: April 2003

AbstractThe surface coverage of porous glass (PD = 500 Å) by styrene adsorbed from its vapor (0.1–6 torr) was studied in a vacuum electrobalance. The adsorption isotherm of the monomer was analyzed by the BET method, and a full monolayer coverage was found to form at a relative pressure of 0.11, weighing 6 mg per gram of glass. Polymerization in submonolayers of adsorbed styrene was initiated by thermal decomposition of predeposited BPO and found to continue until all initiator decomposed, sample cooled, or vapor removed, hence allowing a controlled film thickness. The films were extracted in THF and analyzed by computerized GPC. Molecular weights were in the range 18000–69000. These were related to the rates of polymerization by the usual statistical correlations.
Compatibility of Poly(vinyl chloride) with Polyalkyleneoxides. I. Poly(methylene oxide) and Poly(ethylene oxide)
Authors: Margaritis A. G. , Kalfoglou N. K. 
Published: April 2003

AbstractThe compatibility of poly(vinyl chloride) (PVC) with linear polyethers is examined over the entire composition range. This study examines blends with poly(methylene oxide) (PMO) and poly(ethylene oxide) (PEO) of medium (MMW) and high (HMW) molecular weight. The techniques used are dynamic mechanical analysis, DSC, and optical microscopy (phase contrast and polarizing). The results indicate that all polyethers show limited miscibility in the melt at high PVC contents. Proper analysis of the Tm data using the Kwei‐Frisch and Hoffman‐Weeks procedures allows the determination of the thermodynamic interaction parameter, which is found to be close to zero for all pairs of blends.
Group contribution analysis of the damping behavior of homopolymers, statistical copolymers, and interpenetrating polymer networks based on acrylic, vinyl, and styrenic mers
Authors: Chang M. C. O. , Thomas D. A. , Sperling L. H. 
Published: April 2003

AbstractThe integral of loss modulus versus temperature plots in the vicinity of the glass transition temperature (loss area, LA) was characterized for various homopolymers, statistical copolymers, and interpenetrating polymer networks (IPNs), based on acrylics, vinyls, and styrenic mers. The quantity LA was found to be a molecular characteristic, governed by the structure of the individual mers. The LA of both IPNs and statistical copolymers obeys an additive relation of the component polymers. A group contribution analysis for LA was developed in which each moiety contributes a specific value to LA. A table derived via this group‐contribution analysis permits the prediction of LA values. The results show that backbone motions and the moieties attached directly to the backbone contribute the most to the damping peak, and that long side chains act as diluents.
The role of colloid formation, imidization, and aggregation in the structure of BTDA‐ODA polyimide films modified with gold
Authors: Madeleine D. G. , Ward T. C. , Taylor L. T. 
Published: April 2003

AbstractHigh‐temperature polyimide films with metallic gold surfaces can be fabricated by the incorporation of a soluble metal salt into a solution of polyamic acid. Thermal treatment of these solutions produces the polyimide, decomposes the metal salt to metallic gold, and promotes the formation and growth of the metallized surface. What appeared to be a continuous metallic surface was actually composed of large gold aggregates. It is suspected that the formation of colloidal gold during the initial thermal treatment provides precursors to the large metal aggregates. Thermal treatment has been shown to influence the size and distribution of the aggregates. The shape of the aggregates suggests that diffusion‐limited aggregation may be responsible for the unique shape of some of the gold aggregates.
Fundamental aspects of stress, deformation, and phase transitions in crystallizable polymers: Experiments with poly(ethylene terephthalate) in uniaxial stress fields
Authors: Desai Prashant , Abhiraman A. S. 
Published: April 2003

AbstractInteractions between rheology and fluid→solid transformations through crystallization are demonstrated through an experimental study of crystallization of polyethylene terephthalate in uniaxial stress fields. Effect of the strength of the stress field on the kinetics of crystallization is shown to diminish greatly beyond the initiation of crystallization. Consequences of crystallization in anisotropic stress fields in the generation of mechanical properties are also described. This experimental study points clearly to the deficiencies in current theoretical formulations of kinetics of crystallization.
Structure development of fibers from liquid‐crystalline PET/60PHB copolyester
Authors: Chen G. Y. , Cuculo J. A. , Tucker P. A. 
Published: April 2003

AbstractEffect of extrusion conditions, particularly temperature, on the structure development of fibers from poly(ethylene terephthalate) modified with 60 mol% p‐hydroxybenzoic acid was investigated. Light microscopy revealed that the structure of the liquid‐crystalline fiber was highly dependent on the extrusion temperature: low‐temperature‐spun fibers exhibited a structure with domains or clusters of crystallites randomly oriented, whereas the fibers spun at high temperatures had a well‐developed fibrillar texture. Anisotropy of the fibers, as evidenced by dichroism and by the variation of brightness or darkness of the fibers between crossed polars, was significantly higher for those spun at relatively high temperatures. Scanning electron microscopy revealed that the fibers spun at relatively low temperatures had poorly oriented, nonuniform morphology. Those produced at relatively high temperatures, on the other hand, consisted of well‐developed fibrils. X‐ray diffraction patterns showed that the molecular orientation increased with increasing extrusion temperature. A model for the development of fiber structure from thermotropic liquid‐crystalline polymers is proposed.
Electrical properties of MOS and MIS diodes using an electrochemically prepared poly(N‐methylpyrrole)
Authors: Tsunoda S. , Koezuka H. , Kurata T. , Yanaura S. , Ando T. 
Published: April 2003

AbstractOrganic semiconductor devices using electrochemically prepared poly(N‐methylpyrrole) (PNP) were characterized by capacitance‐voltage (C‐V) measurements. A device with aluminum evaporated on the PNP behaved as a MOS (metal‐oxide semiconductor) diode in vacuum. Assuming the oxide layer between the metal and the PNP to be pure Al2O3, the MOS parameters were calculated. The values obtained for depletion width W = 166 Å and acceptor density NA = 1018 cm−3 in the PNP were reasonable by comparison with the previously reported values obtained by Schottky analysis. An indium/poly(p‐phenylene)‐1,3,4‐oxadiazole (POD)/PNP diode was prepared, and C‐V measurements were carried out in air. The diode behaved like an MIS (metal‐insulator semiconductor) device, but the characteristics showed large variation with frequency. We have proposed a schematic model for this mechanism on the basis of the results obtained by dielectric measurements of POD and the temperature dependence of the MIS characteristics.
Fiber spinning from the nematic melt. V. Flow instabilities in the 75:25 copolyester of p‐hydroxybenzoic acid and 2‐hydroxy‐6‐naphthoic acid
Authors: Krigbaum W. R. , Liu C. K. , Yang D.‐K. 
Published: April 2003

AbstractWe have investigated the rheological properties of the Celanese copolyester with the composition 75 mol% p‐hydroxybenzoic acid and 25 mol% 2‐hydroxy‐6‐naphthoic acid (designated as 75HBA/25HNA). Three different samples having inherent viscosities 3.0, 6.0, and 9.2 dL/g were studied. A flow instability is observed at low shear stress which produces an irregularity in the fiber diameter. The surface irregularity becomes less pronounced above a minimum shear stress, indicating that the flow instability originates in the capillary. For these nematic melts, the minimum shear stress marking the onset of more regular flow is found to decrease with increasing temperature and with decreasing inherent viscosity of the copolyester. The die swell ratio of extrudates decreases with increasing shear stress. Fibers were spun from the samples having ηinh = 9.2 and 3.0 dL/g. The initial modulus and tenacity to break for 75HBA/25HNA fibers spun at sufficiently high shear stress to produce smooth filaments are significantly lower than the values we previously reported for fibers of the 58HBA/42HNA copolyester. Moreover, the optimum properties are obtained at relatively low spin‐draw ratios. The 75HBA/25HNA polyester also exhibits a yield stress which decreases with increasing temperature. This observation indicates the presence of crystallities at the test temperatures. We believe that the higher content of HBA in the present copolymer gives rise to crystallization of HBA blocks in the thread line and that defects are introduced at higher spin‐draw ratios which cause the mechanical properties to become worse.
Analysis of the thermodynamic compatibility of interpenetrating networks during their synthesis
Authors: Cuadrado T. R. , Borrajo J. , Williams R. J. J. 
Published: April 2003

AbstractA thermodynamic analysis of interpenetrating polymer networks (IPNs), at any extent of reaction during their synthesis, is presented for both simultaneous and sequential procedures. A model IPN is assumed to be built up by the independent stepwise homopolymerization of two monomers: a tetrafunctional one, A4, and a trifunctional one, A3. No reaction of copolymerization or grafting is allowed between the two types of polymers. For the case of semi‐IPNs, A3 is replaced by A2, i.e., a bifunctional monomer leading to a linear polymer. The free energy of mixing is described by a Flory‐Huggins lattice model, whereas the elastic contribution is calculated by assuming affine deformation of an ideal elastic network. Results show that a sequential polymerization gives a more incompatible system (i.e., it enters the metastable region at lower conversions) than a simultaneous polymerization starting from the same monomers. In every case, a semi‐IPN is shown to be more compatible than an IPN owing to the fact that the average size of the bifunctional monomer increases less with conversion than the size of the trifunctional monomer. When a sequential polymerization begins from a swollen gel at equilibrium, any increase in the extent of reaction of the solvent monomer will lead to its segregation from the swollen gel. The critical Flory‐Huggins interaction parameter provides a simple way to ascertain the possibility of phase separation during a simultaneous polymerization.
Thermodynamics of miscible polymer blends using a concentration‐dependent χ parameter
Authors: Riedl Bernard , Prud'Homme Robert E. 
Published: April 2003

AbstractThe Flory equation‐of‐state theory, as expressed by Patterson and co‐workers, has been applied to two miscible polymer blends: poly(vinyl chloride)/poly(ε‐caprolactone) and poly(methyl methacrylate)/poly(vinylidene chloride). For both blends, the variation of the polymer‐polymer interaction parameter, χ, as a function of composition, is mostly small and can be accounted for by the Flory theory. However, for poly(vinyl chloride)/poly(ε‐caprolactone) blends, at high poly(ε‐caprolactone content), the large variation of χ as a function of concentration can be explained by a variation of the surface‐to‐volume ratio of the polymers in the mixture with blend composition. The variations of the surface‐to‐volume ratios determined in this study agree with those reported in the literature using small‐angle x‐ray scattering.
Effects of molecular structure and thermal annealing on gas transport in two tetramethyl bisphenol‐A polymers
Authors: Moe M. B. , Koros W. J. , Paul D. R. 
Published: April 2003

AbstractThe effects of molecular structure and thermal history on the gas transport properties of tetramethyl bisphenol‐A polycarbonate (TMPC) and tetramethyl bisphenol‐A polysulfone (TMPSF) are reported. The presence of the bulky methyl side groups on the aromatic rings of TMPC and TMPSF inhibits both chain packing and molecular motions in these polymers as compared with standard polycarbonate and polysulfone. The methyl substitution results in significant increases in permeability with little or no loss of selectivity, making these materials promising candidates for membrane‐based gas separations applications. Thermal annealing produces a densification of the materials, resulting in decreased permeabilities. Selectivities remained roughly the same or increased slightly upon annealing at temperatures slightly below the glass transition temperature. Thus, thermal annealing may be useful for “fine‐tuning” a membrane's properties for applications where improved selectivity is desirable, even at the expense of decreased permeability.
Molecular segregation and nucleation of poly(ethylene oxide) crystallized from the melt. III. Morphological study
Authors: Cheng Stephen Z. D. , Bu H. S. , Wunderlich Bernhard 
Published: April 2003

AbstractSolvent extraction followed by DSC, optical microscopy, and transmission electron microscopy show morphological evidence of molecular segregation for binary mixtures of poly(ethylene oxide)s (PEO). Two segregation types, namely microscopic and macroscopic segregation, have been found. A special etching method for PEO has been developed, and the crystalline textures of bulk samples crystallized at different temperatures for different molecular‐mass mixtures are reported. A linkage between optical and electron microscopy is suggested. The morphology of PEO binary mixtures is crystallization‐temperature and molecular‐mass dependent.
Morphological explanation of the extraordinary fracture toughness of linear low density polyethylenes
Authors: Mirabella Francis M. , Westphal Stanley P. , Fernando Priya L. , Ford Emory A. , Williams J. G. 
Published: April 2003

AbstractThe fracture toughness of commercial linear low‐density polyethylenes (LLDPE) has been found to be extraordinarily high relative to commercial low‐density (LDPE) and high‐density (HDPE) polyethylenes in previously reported investigations. The present investigation shows that this extraordinary fracture toughness cannot be explained by differences in molecular structure variables, such as molecular weight, long‐chain and short‐chain branching, fractional crystallinity, and comonomer content. Instead, the presence of a second soft phase, which was extractable with a weak solvent, in a hard semicrystalline matrix was discovered by morphological investigations of LLDPE resins. This second phase arises from the extreme compositional heterogeneity of the copolymers which comprise these LLDPE resins. No evidence for a similar morphological entity was found in LDPE and HDPE resins. This finding provides persuasive evidence that this very‐low‐crystallinity second phase performs a function similar to that of the rubberlike second phase in other high impact resins and, thus, leads to the observed extraordinary fracture toughness of LLDPE resins. Evidence for the nature and existence of this second phase is given from temperature‐rising elution fractionation and scanning electron microscopy investigations.
Effect of ionizing radiation on the dynamic mechanical properties of an epoxy and a graphite fiber/epoxy composite
Authors: Wilson T. W. , Fornes R. E. , Gilbert R. D. , Memory J. D. 
Published: April 2003

AbstractTGDDM/DDS epoxy and T300/NARMCO 5208 composite specimens were exposed to 0.5 MeV electrons to dose levels up to 10,000 Mrad, and the effects of radiation on the mechanical properties were characterized using dynamic mechanical analysis (DMA). In nominally cured specimens there remain unreacted epoxide groups because the epoxy system vitrifies during the cure, preventing additional reaction. DMA shows that ionizing radiation continues the reactions of epoxide groups. Also, the ultimate glass transition is shown to decrease monotonically with radiation dose. The room temperature elastic modulus of the epoxy increases slightly with radiation, but at temperatures exceeding 100°C there is a slight decrease with radiation. There is a dynamic loss phenomena associated with the composites, not seen in the epoxy, that is thought to be due to the interphase region between the fiber and the matrix.
Polymer complexes stabilized through hydrogen bonds: A semiquantitative theoretical model
Authors: Iliopoulos Ilias , Audebert Roland 
Published: April 2003

AbstractMany studies have been devoted to the formation and behavior of polymer complexes. Unfortunately, the complexity of such systems do not allow a rigorous theoretical approach presently. In this paper we develop a semiquantitative theoretical model for cooperative association between macromolecules. The model is especially adapted for reversible polymer complexes stabilized through weak interactions, e.g., through hydrogen bonds. Theoretical predictions are compared with potentiometric and viscometric experimental results of poly(acrylic acid)/polybase system and a good agreement is established. The influence of parameters such as degree of neutralization of the polyacid, concentration, and molecular weight of polymers is also conveniently predicted.
The cocrystallization of polymers: Polyethylene and its copolymers
Authors: Alamo R. G. , Glaser R. H. , Mandelkern L. 
Published: April 2003

AbstractIn a continuation of our study of the molecular constitution requirements for the cocrystallization of chemically similar polymeric species, we have directed attention to both homopolymer‐copolymer mixtures and copolymer mixtures of polyethylene. Molecular weight and composition fractions were used exclusively. Molecular weights of the components were matched so that attention is given to the influence of chain structure. Differential scanning calorimetry and selective extraction techniques were used to assess whether cocrystallization occurs. Linear polyethylene, and random copolymers which contained up to 2 mol% of either ethyl or acetate branches, cocrystallize upon rapid crystallization from the melt. When the branching content becomes greater than about 3 mol%, cocrystallization does not occur. Copolymers containing about 1–2 mol% are found to cocrystallize with one another. However, copolymers containing higher counit contents do not cocrystallize with one another or with samples containing a smaller amount of counit. These results can be explained on the basis of the concentration of eligible sequences that are available for crystallization.