bluuebunny/crossref_metadata_2025_split huggingface dataset:
A new class of aromatic poly‐ether‐aroyl‐oxadiazoles. II. Studies on the cyclization reaction, infrared, structural, and morphological characterization
Authors: Calandrelli L. , Di Pace E. , Laurienzo P. , Malinconico M. , Martuscelli E. , Volpe M. G. 
Published: April 2003

AbstractPoly‐ether‐aroyl‐oxadiazoles (PEODZ) of general formula: chemical structure image are reported.Thermal cyclization of the starting polyhydrazides, infrared, thermal, and structural characterization are discussed as function of the number of methylene spacers in the range 2–12.It is found that the position of melting is strongly dependent upon the number ofCH2, and that moldable polyoxadiazoles are obtained at × values > 7. The spherulitic nature of PEODZ is clearly revealed by thermal‐optical microscopy which, together with isothermal crystallizations at the differential scanning calorimeter, gives a close insight into the crystalline organization of such polymers. © 1994 John Wiley & Sons, Inc.
FTIR analysis of hydrogen bonding in amorphous linear aromatic polyurethanes. I. Influence of temperature
Authors: Wang Fu Cai , Feve Michel , Lam Thanh My , Pascault Jean‐Pierre 
Published: April 2003

AbstractFourier‐transform infrared spectral studies of an amorphous linear aromatic polyurethane at various temperatures were performed. Hydrogen bonding was studied in the NH stretching (3347 cm−1) and the bending (1535 cm−1) regions, using the band decomposition technique. The variations with temperature are used to calculate the ratio of the absorptivity coefficients for the H‐bonded to the “free” NH vibrations. This ratio is found to be independent of temperature. The enthalpy and the entropy of hydrogen bond dissociation are also obtained as 9.6 kJ mol−1 and 44.8 J mol−1 K−1, respectively. Two CC in‐plane vibrational bands of the aromatic rings at 1614 and 1598 cm−1 were studied at different temperatures. The integrated absorbance for both bands decreases clearly and regularly with increasing temperature, and both bands shift to lower wavenumbers. This strongly suggests a specific interaction for the aromatic rings, probably NH … π hydrogen bonds, which will be discussed in detail in the second part of this series. © 1994 John Wiley & Sons, Inc.
The influence of short‐chain branching on the creep behavior of oriented polyethylene, and its effect on the efficiency of crosslinking by electron irradiation
Authors: Rasburn J. , Klein P. G. , Ward I. M. 
Published: April 2003

AbstractStudies have been made of the creep behavior of oriented (15:1) polyethylenes containing 0.4 and 1.3 butyl branches per 1000 C atoms. Increasing the branch concentration reduces significantly the creep strain and the equilibrium strain rate. The data have been fitted to an established model comprising two thermally activated processes in parallel, relating to the amorphous network at low stress, and the crystal phase at high stress. Analysis based on this model indicates the similarity between branching, entanglements, and crosslinks on the creep response. The creep behavior of electron‐beam‐irradiated materials shows that increasing the branch concentration makes the polyethylene more susceptible to mainchain scission, indicated by increased creep flow rates at higher stress, consistent with previous rubber elasticity studies. Irradiation in an acetylene atmosphere with low (< 1 Mrad) doses is shown to reduce the creep rates at all accessible stresses, and this attributed to an increase in crosslinking compared with scission. © 1994 John Wiley & Sons, Inc.
Syneresis and crystallinity in plasticized rubbery networks and composites
Authors: Pacanovsky J. , Kelley F. N. , Von Meerwall E. 
Published: April 2003

AbstractWe prepared polycaprolactone networks plasticized (60 wt%) with triacetin, with and without filler particles to model high‐energy solid rocket propellants. Under strain and at lower temperatures these materials partially crystallize but also undesirably exude plasticizer (syneresis). We measured both properties isothermally (30°C) on the basis of molecular mobility: crystallinity with rapid‐passage cw proton nuclear magnetic resonance (NMR), and syneresis with pulsed‐gradient spin‐echo NMR diffusion techniques, as a function of strain and time. In the gumstocks crystallinity and syneresis increase monotonically with strain and asymptotically with time. In a given specimen syneresis lags behind crystallinity but they approach the same value, suggesting that syneresis originates in expulsion of plasticizer from crystallizing regions. In the composites, crystallinity results resemble those in gum, but our diffusion data suggest that most syneresis is internal, with plasticizer accumulating in strain‐debonded void regions near filler particles. © 1994 John Wiley & Sons, Inc.
Single‐Molecule single crystals of isotactic polystyrene
Authors: Bu Haishan , Chen Erqiang , Xu Shengyong , Guo Kexin , Wunderlich Bernhard 
Published: April 2003

AbstractSingle‐molecule single crystals were grown from amorphous droplets of fractionated isotactic polystyrene. The crystals were analyzed by electron microscopy and electron diffraction. The molecular mass distribution could be matched with a statistical analysis of single‐molecule particles (amorphous and crystals). Proof was brought that single molecules of isotactic polystyrene do not reach equilibrium dimensions on crystallization, rather assume the lamellar morphology with chain‐folded macroconformation, also known from crystallization of polymolecular crystals. © 1994 John Wiley & Sons, Inc.This article is a US Government work and, as such, is in the public domain in the United States of America. US Government contract No. DE‐AC05‐840R‐21400.
Adsorption‐desorption behavior of phenols on novel polymers containing the pyrrolidinone moiety
Authors: Atobe Ichiro , Takata Toshikazu , Endo Takeshi 
Published: April 2003

AbstractCrosslinked polymers having a pyrrolidinone moiety (CPS, CPES, and CVP) were synthesized by radical copolymerization of 4‐(2‐oxo‐1‐pyrrolidinyl)methylstyrene, 4‐[2‐(2‐oxo‐1‐pyrrolidinyl)ethoxy]methylstyrene, or 2‐vinylpyrrolidinone with divinylbenzene in the presence of AIBN as a radical initiator. The adsorption‐desorption behavior of phenols on these polymers was investigated. The polymers with spacers between the polymer main chain and pyrrolidinone moiety appeared to have a superior adsorption capability to those without such spacers. The amount of phenol adsorbed on the polymers in a solvent decreased in the following order: water > chloroform > methanol. In methanol, the interaction between the polymers and phenol was suggested to come only from charge‐transfer stacking (C–T stacking), whereas in chloroform the interaction was caused mainly by both hydrogen bonding and C–T stacking. The interaction in water was attributed not only to both hydrogen bonding and C–T stacking, but also to a hydrophobic interaction. Characterization of polymers (CVP) containing adsorbed phenol was carried out by thermogravimetric analysis (TGA). The TGA curves indicated a two step weight‐decrease, namely the first step in the temperature ranging from ca. 100‐200°C was attributed to the desorption of phenol while the second step in the temperature ranging from ca. 350‐500°C was based on thermal decomposition of the polymers. The desorption of phenol adsorbed on the polymers in water indicated an inverse tendency to the adsorption; that is, the amount of phenol desorbed from the polymers without a spacer was more than those from the polymers with spacers. © 1994 John Wiley & Sons, Inc.
Plasma‐enhanced deposition of diamond‐like carbon films on high temperature tolerant polymers
Authors: Freeman Mathieu J. , Harding David R. 
Published: April 2003

AbstractThe feasibility of depositing carbon films with a diamond‐like structure on high temperature polymers, using established plasma‐enhanced chemical vapor deposition techniques, is explored. Potential uses for such a film will depend upon the adhesion of the film to the substrate, the properties of the deposited film, and the effect of the deposition process on the bulk properties of the polymer substrate.Amorphous carbon (diamond‐like carbon) coatings with thicknesses ranging from 2 to 18 μm were deposited on polyimide substrates at temperatures below 420°C. Extended exposure to the plasma processing conditions caused no visible damage but halved the room‐temperature tensile strength of the polymer films. Diamond‐like carbon, graphitic carbon, and a precursor to the diamond‐like carbon structure, attributed to an aromatic carbon ring structure, were observed. The optical transparency of the coated polymer film was attenuated uniformly across the spectral range, 2.5‐22 μm. Static oxidation and limited thermal cycling of the coated polymer produced no widespread delamination of the coating from the substrate: neither the deposited film nor the coated regions of the polymer showed any effect when oxidized at 370°C, for 450 h. © 1994 John Wiley & Sons, Inc.
Thermal conductivity of poly(ether ether ketone) and its short‐fiber composites
Authors: Choy C. L. , Kwok K. W. , Leung W. P. , Lau Felix P. 
Published: April 2003

AbstractThe effects of crystallinity, orientation, and short‐fiber filler on the thermal diffusivity D and thermal conductivity K of poly (ether ether ketone) (PEEK) have been studied. Below the glass transition, D increases by less than 10% as the crystallinity increases from 0 to 0.3. For amorphous PEEK, there is an abrupt drop in D at the glass transition (Tg ⋍ 420 K). The drop is less prominent for the 30% crystalline sample and occurs at 20 K higher. At a draw ratio of 2.5, the axial thermal conductivity is 2.3 times higher while the transverse thermal conductivity is 30% lower than that of the unoriented material. For an injection‐molded bar of carbon fiber reinforced PEEK, the variation of D with position along the width or thickness direction is found to correlate well with the fiber orientation. By regarding the injection‐molded bar as a multidirectional laminate comprising a large number of unidirectional plies, the thermal conductivities along the longitudinal and transverse direction are calculated and found to agree closely with the experimental data. © 1994 John Wiley & Sons, Inc.
An improved model for mass transfer during the formation of polymeric membranes by the immersion‐precipitation process
Authors: Cheng Liao‐Ping , Soh Young S. , Dwan An‐Hwa , Gryte Carl C. 
Published: April 2003

AbstractAn analysis is presented, which describes the isothermal ternary diffusion process encountered in the formation of a cellulose acetate polymeric membrane by a direct immersion‐precipitation of polymeric solutions in a nonsolvent bath. A material coordinate was employed to derive the mass transfer equations for the membrane solution and the convective mass transfer in the coagulation bath was taken into account by solving the hydrodynamic boundary layer equations. Diffusion coefficients were measured and used to deduce ternary phenomenological coefficients. The computed results are found to agree with the experimental precipitation time and membrane morphologies observed in scanning electron photomicrographs. © 1994 John Wiley & Sons, Inc.
Light‐Scattering evidence of a “critical” concentration for polymer coil shrinking in dilute solution
Authors: Wu Chi 
Published: April 2003

AbstractThe variation of polymer chain dimension with concentration in both dilute and extremely dilute solutions was monitored by measuring the diffusivity of narrowly distributed poly‐styrene standards in toluene at room temperature through a carefully designed dynamic light scattering experiment. As polystyrene concentration decreases, the measured translational diffusion coefficient levels off after a certain concentration, i.e., in terms of experimental results, there exists a “critical” concentration for polystyrene coil shrinking in dilute toluene solution. The existence of this critical concentration has been predicted by introducing the concept of screening length into the statistical thermodynamic calculation. In this paper, we report, for the first time, its laser light‐scattering evidence. © 1994 John Wiley & Sons, Inc.
Doi‐Edwards theory evaluation in double‐step strain flows
Authors: Venerus D. C. , Kahvand H. 
Published: April 2003

AbstractIt is widely accepted that for reversing double‐step strain deformations, predictions based on the Doi‐Edwards (DE) molecular theory without the independent alignment approximation (IAA) are superior to predictions obtained with the IAA, or equivalently, the Kaye‐Bernstein‐Kearsley‐Zapas (K‐BKZ) theory. This summation, however, is based on data obtained over limited ranges of strain and time: the time both between the step strains (t1) and following the second step strain (t–t1). In this study, a thorough evaluation of the DE theory is carried out using a comprehensive double‐step strain flow data set. The results of this study indicate that the DE theory is an improvement over the K‐BKZ theory in flows with strain reversal but only for cases when the criteria t1, t–t1 ≫ τk is satisfied. The constant τk, defined as the time beyond which the stress relaxation modulus is factorable: G(γ, t) = h(γ)G(t), is believed to represent the end of the chain retraction process in the DE theory. It appears that the dynamics of chain retraction have an important influence on double‐step strain behavior and, therefore, should be accounted for in molecular‐based theories devised to have general validity in this important deformation history. © 1994 John Wiley & Sons, Inc.
PVT properties of dodecane/polystyrene systems
Authors: Kim Dukjoon , Caruthers James M. , Peppas Nikolaos A. 
Published: April 2003

AbstractThe PVT properties of crosslinked polystyrene samples containing various amounts of dodecane were measured. The Tait equation was used to describe the PVT behavior of each system in both the glassy and rubbery regions. The glass transition temperature was determined from the abrupt change of the thermal expansion coefficient. Increase in the dodecane content in the samples resulted in a significant decrease of the difference between the expansion coefficients in the glassy and rubbery regions. Addition of dodecane lowered the glass transition temperature linearly. However, the dependence of the glass transition temperature on pressure was not affected by the presence of dodecane in the polymer samples. Above the glass transition temperature, the volume of the swollen polymer, Vm, could be determined by simple addition of the volumes of the pure components at the appropriate temperature and pressure; the volume change of mixing, δVm, was independent of temperature and pressure. Below the glass transition temperature, volume additivity of the two components was also applicable after appropriate adjustment of the glass transition temperature of the polymer to that of the dodecane/polymer samples. © 1994 John Wiley & Sons, Inc.
Dielectric relaxations in poly(thiocarbonates)
Authors: Calleja R. Díaz , Gargallo L. , Radić D. 
Published: April 2003

AbstractThe dielectric absorptions observed on six poly(thiocarbonates) (PTC) containing different substituents in the interphenylic carbon atom are subjected to a study. The α relaxation process associated with the glass transition temperature, which appears at the highest temperature studied, is overlapped with a strong conductive component. Between 80 and 100°C dielectric activity (β) is observed, which is related to structural relaxation phenomena. Polymers with double substitution on the interphenylic carbon atom show a γ relaxation with an activation energy of ca. 11 kcal mol−1 while those where the carbon atom is linked to a cyclohexyl group show higher activation energies and their respective characteristics. A cryogenic absorption around −120°C, for at least three polymers with an activation energy of about 5 kcal mol−1, is detected. © 1994 John Wiley & Sons, Inc.
Aspects of polymer surface characterization by inverse gas chromatography
Authors: Mukhopadhyay Prithu , Schreiber H. P. 
Published: April 2003

AbstractThe inverse gas chromatographic method has been used to evaluate dispersive surface energies and acid/base interaction values for a styrene/maleic anhydride copolymer over a substantial temperature range. Surface energy calculations require knowledge of the dimensions of adsorbed molecules; conventional values of these for linear alkanes result in reliable surface energy data at near‐ambient temperatures. Above about 60°C, however, more reliable surface energy data are obtained when the dimensions of the adsorbed species are corrected by density/temperature variations of the vapors. The copolymer studied was shown to be amphoteric, but with an appreciable prevalence of basic surface sites. © 1994 John Wiley & Sons, Inc.
Effect of styrene‐4‐vinyl pyridine diblock copolymer on morphological, thermal, and mechanical properties of poly(2,6‐dimethyl‐1,4‐phenylene ether)/polyethylene ionomer blends
Authors: Jo Won Ho , Jo Byoung Cheon , Cho Jae Cheol 
Published: April 2003

AbstractThe compatibilizing effects of a styrene‐4‐vinyl pyridine diblock copolymer on the properties of immiscible poly(2,6‐dimethyl‐1,4‐phenylene ether) (PPE)/polyethylene ionomer (Surlyn) blends are investigated by examining the phase morphology and the thermal and mechanical properties. The block copolymer is synthesized by sequential anionic polymerization at −78°C and melt‐mixed with PPE and Surlyn at 290°C. When a small amount of block copolymer is present, the domain size of the dispersed phase becomes smaller. The tensile strength and elongation at break increase with addition of the block copolymer for PPE‐rich matrix blends, whereas the tensile strength increases but the elongation at break decreases for Surlyn‐rich matrix blends. These effects are interpreted in terms of the interfacial activity and the reinforcing effect of the block copolymer. From the experimental results, it is concluded that the block copolymer plays a role as an effective compatibilizer for PPE/Surlyn blends. © 1994 John Wiley & Sons, Inc.
Poly[(methylene oxide) oligo(ethylene oxide)] vs. poly(ethylene oxide) as hosts for neodymium compounds
Authors: Twomey Conor J. , Chen Shaw H. , Blanton Thomas N. , Schmid Ansgar , Marshall Kenneth L. 
Published: April 2003

AbstractIn view of the residual crystallinity in PEO found to limit the solubility of some Nd3+‐compounds, amorphous PEO (aPEO) was synthesized for exploration as an alternative host. Complexation, solubility limit, morphology, and response to moisture absorption in the doped systems were investigated using FTIR, DSC, TGA, and WAXD techniques. Representing a perturbation to the structural regularity present in PEO, aPEO was found to present lower solubilities for dopants (Nd(act)3 and Nd(acac)3, both characterized by a weak Nd3+–ether oxygen interaction. On the other hand, no difference in solubility was observed for dopant Nd(NO3)3, characterized by a strong Nd3+–ether oxygen interaction. Laser interferometry was employed to assess film homogeneity of the Nd(NO3)3‐doped systems across a 20‐mm diameter, and the measured peak‐to‐valley distortion values were observed to be encouraging for practical applications. © 1994 John Wiley & Sons, Inc.
Towards understanding the increase in strength of thermotropic polyesters with heat treatment
Authors: Warner S. B. , Lee J. 
Published: April 2003

AbstractThermotropic copolyester fibers of oxynaphthoate and oxybenzoate have been subjected to conditions that promote solid‐state polymerization as well as annealing. The annealing process causes the crystals to perfect with a simultaneous increase in heat of fusion and melting temperature. Solid‐state polymerization, a reaction rate‐controlled process, causes the polymer viscosity average molecular weight to increase by chain extension from about 14,000 g/mole to more than 87,000 g/mole with a simultaneous impressive increase in tenacity from about 10 g/d (1.2 GPa) to almost 30 g/d (3.7 GPa). To understand the changes in mechanical properties, we have modeled the fiber structure as short rod‐like molecules poorly bonded to a continuous matrix of parallel molecules. Lengthening of the reinforcing molecules facilitates better transfer of load from matrix to molecules, resulting in higher tenacity fibers. © 1994 John Wiley & Sons, Inc.
Thermal characterization of tetrafluoroethylene‐perfluoroalkylvinylether copolymers: Melting behavior and low‐temperature transitions
Authors: Pucciariello Rachele 
Published: April 2003

AbstractDifferential scanning calorimetry has been used to study the melting and the low‐temperature transitions of tetrafluoroethylene‐perfluoroalkylvinylether copolymers (PFA). Melting is similar to that of PTFE in that it is subject to superheating, moreover the melt‐crystallized samples show temperatures and heats of fusion lower than the native ones. At temperatures lower than room temperature, crystal‐crystal transitions are observed for copolymers containing 2 mol % of perfluoromethyl‐, perfluoroethyl‐, and perfluoro‐n‐propylvinylether. In the case of perfluoromethylvinylether as a comonomer, low‐temperature transitions are present only up to a content of 4 mol %. The effect on melting and low‐temperature transitions of both the comonomer content and of the type of side groups has been investigated. The temperatures and heats of transitions show the expected dependence as a function of the comonomer concentration and have been found to be independent on the chemical nature of the side group. © 1994 John Wiley & Sons, Inc.
Surface stress‐dependent adhesion to fluorinated polymers
Authors: Rye R. R. 
Published: April 2003

AbstractIrradiation of thin commercial sheets of poly(tetrafluoroethylene) (PTFE) or a fluorinated ethylene‐propylene copolymer (FEP) yield essentially the same results with mass spectroscopy or x‐ray photoelectron spectroscopy (XPS). For both gas phase and surface (ca. 30 Å) products of irradiation, the same product distributions and exposure dependencies are observed. In addition, XPS of chemically etched (with sodium naphthalenide) PTFE and FEP shows the same extent of surface defluorination. In contrast to the more surface‐sensitive XPS, Rutherford backscattering spectroscopy of etched PTFE shows that the defluorination extends to depths of ca. 3000 Å, while with etched FEP defluorination extends to only a few hundred Angstroms. Scanning electron microscopy shows the FEP surface to be smooth and featureless both before and after chemical etching, while etched PTFE is characterized by a crazed surface with a high density of unidirectional cracks oriented perpendicular to long macroscopic scratches existing in the virgin surface. Adhesion of Cu to this etched PTFE has previously been shown to be sufficiently strong that failure is a result of near‐cohesive failure in the PTFE and not adhesive failure. Conversely, weak adhesion of Cu to etched FEP or to other smooth forms of fluorinated polymers, including polished PTFE, is observed. This correlation of strong adhesion with surface roughness and not with surface chemical changes is consistent with previous suggestions that a major component of adhesion to fluorinated polymers is mechanical interlocking. The differences between FEP and PTFE are discussed in terms of a model involving surface stresses expected from their different methods of manufacture: extrusion from the melt in the case of FEP and skiving from pressed cylinders in the case of PTFE. © 1994 John Wiley & Sons, Inc.