bluuebunny/crossref_metadata_2025_split huggingface dataset:
Liquid–liquid transition in polymers and glass‐forming liquids
Authors: Murthy S. S. N. 
Published: April 2003

AbstractIt is shown that many simple glass‐forming liquids exhibit a phenomenon known in the area of polymer science as the liquid–liquid transition. The phenomenon manifests itself as a third‐order transition in the equilibrium liquid‐specific heat data around approximately 1.2 Tg and also as a bifurcation of the liquid relaxation into primary and secondry processes. It is stressed that the above phenomenon is due to a smooth changeover of the liquid from one dynamic regime to the other and hence is not due to any real phase transition. It is suggested that a liquid cluster kind of picture for the supercooled liquid regime, is capable of explaining the above phenomenon and is consistent with observation made on polymers and monomeric liquids. © 1993 John Wiley & Sons, Inc.
Interconversion between mechanical and dielectric relaxations for poly(cyclohexyl acrylate)
Authors: Díaz‐Calleja Ricardo , Riande Evaristo , Román Julio San 
Published: April 2003

AbstractStorage E′ and loss E″ relaxation moduli are reported as functions of frequency for poly(cyclohexyl acrylate) (PCA) at several temperatures. The possibility that these results, in conjunction with the dipolar correlation coefficient, can be used to predict the frequency dependence of the real ε and loss ε″ and the components of the complex dielectric permittivity ε* of PCA is studied. A relation between ε* and the complex relaxation modulus E* is obtained by assuming that the lag of the rotating dipoles in the electric field is caused by both dielectric and mechanical friction. The values of ε* obtained from mechanical results by means of this expression are very close to those obtained from other relations based on the assumption that the lag of the dipoles is caused exclusively by mechanical friction. © 1993 John Wiley & Sons, Inc.
Broadening of the glass transition in blends of poly(aryl ether ketones) and a poly(ether imide) as studied by thermally stimulated currents
Authors: Sauer Bryan B. , Hsiao Benjamin S. 
Published: April 2003

AbstractBlends of poly(aryl ether ketones) (PAEKs) and an amorphous poly(ether imide) (PEI) were used as model systems to study the broadening of the glass transition due to crystallization and the resulting depletion of PAEK from the amorphous phase. Two different PAEKs were studied, which are completely miscible with PEI in the amorphous state; poly(aryl ether ether ketone) (PEEK) and a slower crystallizing poly(aryl ether ketone ketone)(PEKK). Relatively rapid crystallization conditions were chosen in order to trap a significant fraction of PEI between the PAEK crystal lamellae or between bundles of lamellae. The broad glass transitions are apparently a result of the nonuniform nature of this process. The breadth of the glass transition was quantified by thermally stimulated currents (TSC) applied in the thermal sampling (TS) mode. The results compared favorably with DSC data. The magnitude of the apparent activation energy obtained by the TS method allows one to assign the relaxations as cooperative (glass transition‐like) or non‐cooperative and to define the limits of the glass transition with a higher degree of precision than other techniques. Cooperative relaxations can be resolved with this technique, even if they are only a small fraction of the overall relaxing species at a given temperature. In some cases the glass transition region was found to broaden to ca. 60°C after crystallization. © 1993 John Wiley & Sons, Inc.
Permeation and sorption in polynorbornenes with organosilicon substituents
Authors: Bondar V. I. , Kukharskii Yu. M. , Yampol'skii Yu. P. , Finkelshtein E. Sh. , Makovetskii K. L. 
Published: April 2003

AbstractGas sorption properties, permeability coefficients, and diffusion coefficients of a series of norbornene polymers are presented. Introduction of the Si(CH3)3 group into the polynorbornene (PNB) backbone chain results in significant increases in glass transition temperature, permeability, and diffusion coefficient for a number of gases (H2, O2, N2, CO2, CH4, C2H6). The transport properties and sorption isotherms for poly(5‐trimethylsilyl norbornene) (PTMSNB) are very similar to those for poly(vinyltrimethyl silane) (PVTMS), which contains the same side‐chain group but differs from PTMSNB by the structure of its main chain. For another silicon‐containing polymer poly[5‐(1,1,3,3‐tetramethyl‐1,3‐disilabutyl) norbornene] (PDSNB) having a bulkier side‐chain group, the glass‐transition temperature is decreased in comparison with that of PNB, presumably owing to self‐plasticization. Both silicon‐containing norbornene polymers (PTMSNB and PDSNB) have permeability coefficients for “rapid” gases like H2 or CO2 of about 102 Barrer. The high values of the Langmuir sorption capacity C′H for PTMSNB and PVTMS, as well as the high diffusivity and mobility of spin probes in these polymers, were attributed to a large free volume related to the bulky Si(CH3)3 groups attached directly to the main chain. © 1993 John Wiley & Sons, Inc.
Ar atom emission as a probe of craze formation and craze growth in polystyrene
Authors: Dickinson J. T. , Jensen L. C. , Langford S. C. , Dion R. P. 
Published: April 2003

AbstractA report of measurements of Ar emission during the loading of polystyrene and high impact polystyrene in vacuum is presented. Argon was introduced into the material prior to the experiment by storing the samples in an Ar atmosphere. The development of crazes during loading was monitored by videotaped visual observations and scattered light measurements. Increased Ar emission is observed at the onset of crazing, provided that the crazes intersect the surface. The strength of the Ar signal depends upon the extent of crazing; especially intense signals are observed from samples which display significant crazing prior to fracture. High‐impact polystyrene shows intense emissions at yield which soon decay due to the depletion of Ar from the near surface material. The emission intensity rises again prior to fracture, when surface crazes become connected to crazes in the bulk. Thus the emission of volatile species during deformation reflects the growth of crazes intersecting the surface, as well as changes in the “connectivity” of the craze network. © 1993 John Wiley & Sons, Inc.
Dipole moment and dielectric relaxation of poly(dimethylsilazane) oligomers
Authors: Salom Catalina , Riande Evaristo , Hernändez‐Fuentes Irmina , Dïaz‐Calleja Ricardo 
Published: April 2003

AbstractThe polarity of polysilazane chains is studied using as models hexamethyldisilazane (HMDSZ) and an oligomer of amine‐terminated poly(1,1‐dimethylsilazane) (PDMSZ). Solvent effects and the contribution of the atomic polarization to the dipole moment of both PDMSZ and HMDSZ are discussed. A qualitative interpretation of the dipole moment of the oligomer suggests that gauche states about the skeletal bonds may be disfavored with respect to the alternative trans states. The dielectric spectrum of PDMSZ presents a glass‐rubber relaxation followed by two weak secondary absorptions. The experimental results show that the relaxation strength Δε of PDMSZ is lower than that corresponding to poly(1,1‐dimethylsiloxane) (PDMS). The analysis of the glass‐rubber relaxation by using the coupling scheme suggests that strong intermolecular interactions occur in the chains that presumably arise from hydrogen bonding interactions between amine groups. © 1993 John Wiley & Sons, Inc.
Compatibility and crystallization in poly(ethylene oxide)‐poly(methyl methacrylate) semi‐interpenetrating polymer network
Authors: Ahn Sung‐Hee , An J. H. , Lee D. S. , Kim S. C. 
Published: April 2003

AbstractDifferential scanning calorimetry together with dynamic mechanical analysis were employed to investigate the crystallinity and the miscibility in poly(ethylene oxide)/crosslinked poly(methyl methacrylate) semi‐IPN (interpenetrating polymer networks). The crystallinity of poly(ethylene oxide) in the semi‐IPN is found to depend on the crosslink density of PMMA as well as the overall content of PEO. Of special interest is that an increase in the crosslink density tends to increase the crystallinity contrary to our expectation, indicating crystallization and phase separation may proceed simultaneously during IPN formation. The investigation of glass transition behaviors with dynamic mechanical analysis suggests phase separation (i.e., there exist two amorphous phases: one PEO‐rich phase, the other a PMMA‐rich phase). © 1993 John Wiley & Sons, Inc.
On the solution characterization of an all‐aromatic liquid‐crystalline copolyester
Authors: Cinquina P. , Cam D. , Tampellini E. , Chapoy L. L. 
Published: April 2003

AbstractSolution characterization of the thermotropic liquid–crystalline copolyester synthesized from terephthalic acid, phenyl hydroquinone, and (1‐phenylethyl) hydroquinone (2 : 1 : 1) has been performed. Viscometry, size exclusion chromatography, and light scattering have been carried out under the optimal conditions found for measurement: 85°C in a 50/50 mixture by weight of phenol/1,2,4‐trichlorobenzene. The absolute weight‐average molecular weight from light‐scattering measurements served for calibration of indirect methods of charac‐terization (e.g., the limiting viscosity number [η] is related to the molecular weight by [η] = 5.10 × 10−4 Mw0.72), and the molecular weight per unit chain length, \documentclass{article}\pagestyle{empty}\begin{document}$ \bar M_L * $\end{document}, from light scattering and size exclusion chromatography (SEC) is found to be 28 Å−1, consistent with theoretical expectations. The calculated persistence length q is 28 Å. Moreover, the meth‐odology of SEC characterization enables the kinetics of solid‐state postpolymerization of this liquid‐crystalline copolyester to be studied. © 1993 John Wiley & Sons, Inc.
Structure and compatibility of poly(vinyl alcohol)‐silk fibroin (PVA/SA) blend films
Authors: Tsukada Masuhiro , Freddi Giuliano , Crighton John S. 
Published: April 2003

AbstractThe structure and compatibility of poly(vinyl alcohol)‐silk fibroin (PVA/SF) blend films were analyzed by differential scanning calorimetry (DSC), thermomechanical (TMA) and thermogravimetric (TGA) analysis, x‐ray diffractometry, and scanning (SEM) and transmission (TEM) electron microscopy. DSC curves of PVA/SF blend films showed a major endothermic peak at 220°C, along with a peak at 280°C. These endotherms were assigned to the thermal decomposition of the ordered PVA elements and to the thermal degradation of silk fibroin, respectively. The PVA/SF blends behaved in a manner intermediate to the pure components, as suggested by both contraction expansion and sample weight retention properties recorded by TMA and TGA measurements. The IR absorption spectra of the blends were identified as purely a composite of the absorption bands characteristic of both PVA and SF pure polymers. The X‐ray diffraction patterns of PVA/SF blends showed overlapping spacing due to PVA and SF. A dispersed phase formed by spherical particles of 3–7 μm diameter was observed by SEM and TEM. All these findings suggest that PVA and SF are incompatible. © 1994 John Wiley & Sons, Inc.
Gel spinning of poly(vinyl alcohol) from dimethyl sulfoxide/water mixture
Authors: Cha Won‐Ill , Hyon Suong‐Hyu , Ikada Yoshito 
Published: April 2003

AbstractGel spinning of poly(vinyl alcohol) (PVA) was attempted from the PVA dope prepared from the mixture of dimethyl sulfoxide (DMSO) and water. The DMSO/H2O = 80/20 (w/w) mixture and methanol were found to be the best solvent for the spinning dope and the coagulant, respectively, to give PVA fiber with the highest drawability. PVA fiber with the highest strength and Young's modulus were obtained from the undrawn gel fibers when subjected to hot two‐stage drawing under conditions such as to produce maximum drawability. Furthermore, higher draw ratios of PVA fiber were attained at 6 wt % dope by lowering the coagulating temperature of methanol. In the present work, the highest tensile strength (2.8 GPa) and the highest Young's modulus (64 GPa) were realized, when the spinning dope was prepared from PVA with DP of 5,000 and the DMSO/H2O (80/20) mixed solvent to have the PVA concentration of 6 wt %, the coagulating temperature of methanol was −20°C, and the two‐stage drawing was carried out at 160 (first) and 200°C (second). The PVA fiber prepared under this gel spinning condition could be elongated to 45 times draw ratio. The very high drawability of PVA fibers obtained from the DMSO/H2O (80/20) mixture dope was ascribed to the ability of the DMSO/H2O mixture to promote gelation. © 1994 John Wiley & Sons, Inc.
The use of near infrared (NIR) spectroscopy to study specific interactions in polymer blends
Authors: Ghebremeskel Yacob , Fields Jeffrey , Garton Andrew 
Published: April 2003

AbstractThe purpose of this brief communication is to demonstrate how near infrared (NIR) spectroscopy can be used to study specific interactions is miscible polymer blends. We will first demonstrate, using model systems and blends of polycaprolactone (PCL) and phenoxy [poly(hydroxypropylether of bisphenol‐A)], that information obtained from the OH stretch overtone absorption in the NIR is consistent with the information obtained from the OH stretch fundamental in the mid‐IR region. We will then illustrate the advantages of NIR analysis of specific interaction with spectra obtained, over a range of temperatures, from thick (2 mm) films of blends of Nylon‐6 and the zinc salt of sulfonated polystyrene (ZnSPS). © 1994 John Wiley & Sons, Inc.
Design of anhydrous electrorheological (ER) suspensions based on I2‐doped poly(pyridinium salt)
Authors: Yu Wei‐Ching , Shaw Montgomery T. , Huang Xiao‐Yan , Harris Frank W. 
Published: April 2003

AbstractA rigid‐rod aromatic poly(pyridinium salt) was synthesized and doped with iodine (I2) for making anhydrous electrorheological (ER) fluids. The I2‐doped particles were further processed into ones having insulating skins. Dielectric properties and current densities of the suspensions containing these particles were studied to elucidate the roles of conductivity of the dispersed phase in the ER suspension. © 1994 John Wiley & Sons, Inc.
Crystallinity of fully aromatic thermotropic polyesters of 3,3'‐bis(phenyl)‐4,4'‐biphenol and 1,1'‐binaphthyl‐4,4'‐diol
Authors: Bhowmik Pradip K. , Beaucage Gregory , Bhattacharya Subrata K. , Lenz Robert W. 
Published: April 2003

AbstractThe degree of crystallinity of as‐made fully aromatic, thermotropic polyesters was determined for two different series of polymers, each of which contained a symmetric monomer having either pendant phenyl groups or fused aromatic rings by the WAXD technique. All of the homopolymers had a high degree of crystallinity in spite of bulky substituents attached to the mesogenic moiety. Surprisingly, the homopolymer of 2,6‐naphthalenedicarboxylic acid with each of the monomers had a higher degree of crystallinity and Tm than those of the homopolymer of terephthalic acid with each of the respective monomers. As expected, on copolymerization with 30 mol % of either 4‐hydroxybenzoic acid or 6‐hydroxy‐2‐naphthoic acid, all of the resulting copolymers had a much lower degree of crystallinity and Tm/Tf values compared to those of the respective homopolymers in each series. © 1994 John Wiley & Sons, Inc.
Molecular modeling of polymers. 10. Characterization of conformational transitions of poly(acrylic acid) and poly(methacrylic acid) using dyad structures
Authors: Ravi M. , Hopfinger A. J. 
Published: April 2003

AbstractThe conformational profiles of nearest side‐chain neighbors, methylene‐dyad structures, of poly(acrylic acid), PAA, and poly(methacrylic acid), PMA, were determined as a function of tacticity, extent of ionization, and presence of counterion. The dominant backbone conformer states are quite similar for both isotactic and syndiotactic diads in a common charge state. Thus, the overall dimensional properties of isotactic syndiotactic and atactic chains of PAA or PMA, based upon dyad interactions, are predicted to be alike for a given charge state. Significant deviations from precise t, g+, and g− states are found for the dyad minimum energy conformations. The rod‐to‐coil and coil‐to‐rod transitions observed in PAA and PMA, respectively, as a function of increasing counterion concentration can be explained, to a large extent, by the conformational profiles of the corresponding dyad model structures. © 1994 John Wiley & Sons, Inc.
Relaxation behavior, intramolecular interactions, and local motions on monosubstituted esters of poly(itaconic acid)
Authors: Díaz‐Calleja Ricardo , Saiz Enrique , Riande Evaristo , Gargallo Ligia , Radic Deodato 
Published: April 2003

AbstractThe mechanical relaxation spectrum of poly(monocyclohexylmethylene itaconate) (PMCMI) exhibits two well‐developed absorptions in the glassy state that in increasing temperature order are named γ and β absorptions. Owing to the restricted conformational versatility of the backbone, the polymer presents a weak glass‐rubber relaxation whose intensity is significantly lower than that of the γ absorption. Comparison of the mechanical spectrum of this polymer with that of poly(dicyclohexylmethylene itaconate) (PDCMI) allows the conclusion that the β relaxation is produced by motions in which the COOCH2C6H11 side groups are involved. The location of the mechanical γ peak suggests that this absorption is produced by flipping conformational transitions in the cyclohexyl residue. Three dielectric absorptions are observed in the glassy state of PMCMI which in increasing temperature order are called δ, γ, and β relaxations. Both the location and the activation energy of the dielectric and mechanical β absorptions suggest that both relaxations are caused by the same molecular motions. Dipolar interactions in the liquid and glassy state are calculated and the results compared with those experimentally evaluated. © 1994 John Wiley & Sons, Inc.
Double ferroelectric‐to‐paraelectric transition in 70/30 vinylidene fluoride‐trifluoro ethylene copolymer as revealed by dielectric spectroscopy
Authors: Ezquerra T. A. , Kremer F. , Baltá‐Calleja F. J. , Lopez Cabarcos E. 
Published: April 2003

AbstractThe variation of dielectric properties with temperature in the 1 kHz to 1 GHz frequency range for the 70/30 copolymer of vinylidene fluoride with trifluoroethylene has been associated to two processes: the β relaxation process associated with the glass transition of the amorphous phase and the ferroelectric‐to‐paraelectric crystal transition. The β process follows a Vogel‐Fülcher behavior exhibiting an anomaly in the vicinity of the crystal transition. Analysis of the ferroelectric‐to‐paraelectric Curie transition reveals the existence of a double relaxation maximum in the dielectric losses. Results have been interpreted in terms of the Havriliak‐Negami relaxation function. The variation of the relaxation strength and of the broadening parameter has been investigated as a function of temperature. The obtained results are discussed in terms of a two‐step phase transformation mechanism for the Curie transition: a first transition from the low temperature “all‐trans” ferroelectric phase to a more defective phase; a second transition from the latter phase to the final paraelectric structure. © 1994 John Wiley & Sons, Inc.
Interfacial bonding, energy dissipation, and adhesion
Authors: Gent A. N. , Lai S.‐M. 
Published: April 2003

AbstractThin sheets of several elastomers have been adhered together by CC or SS interfacial bonds and peeled apart at various rates and temperatures. For CC bonding, values of the work G required per unit area to separate the sheets could be superposed to form a master curve versus peel rate using Williams‐Landel‐Ferry (WLF) temperature shift factors. Threshold values Go at low rates and high temperatures ranged from virtually zero for nonbonded sheets up to the tear strength of the sheet itself, 50‐80 J/m2, for fully interlinked sheets, in proportion to the density of interfacial bonds. The strength thus appears to be the sum of two terms: Go and a viscoelastic loss function which itself is approximately proportional to Go. By comparing the dependence of G upon rate of peel with the dependence of dynamic shear modulus μ′ upon oscillation frequency, an effective length of the fracture zone was deduced. It was extremely small in all cases, only about 1 Å. With sulfur interlinks, values of G were larger at all peel rates and varied more with temperature than predicted by the WLF relation. This is attributed to a concomitant decrease in SS bond strength with temperature, and an increase in energy dissipation as the weaker sulfur bonds fail. © 1994 John Wiley & Sons, Inc.
Thermal and structural analysis and crystallization behavior of new poly(ether‐alkyl) oxadiazoles
Authors: Pace E. Di , Fichera A. M. , Laurienzo P. , Malinconico M. , Martuscelli E. , Perenze N. , Volpe M. G. 
Published: April 2003

AbstractA new series of poly(ether‐alkyl)oxadiazoles of general formula:

with m = 3, 4, and 5 has been obtained from the corresponding polyhydrazides through thermal cyclization reaction. The polymers were characterized by infrared spectroscopy, differential scanning calorimetry, wide‐angle x‐ray analysis, and optical microscopy. The polymers were crystalline, with a crystalline texture and structural parameters strongly dependent on the value of m. The Tm's and Tg's value decreased with increasing number of CH2. © 1994 John Wiley & Sons, Inc.
Study of PVB aggregation process by electron microscopy
Authors: Zhang Yanfei , Sun Hongjian , Shen Jiarui 
Published: April 2003

AbstractThe structure of aggregates formed from poly(vinyl butyral) (PVB) in tetrahydrofuran (THF) was studied by transmission electron microscopy (TEM). We have found that the primary associated particles are nearly spherical and, as the association advances, the particles lengthen. Eventually aggregates branch to form a three‐dimensional network. The bulk PVB was investigated by scanning electron microscopy (SEM). We have found that the bulk PVB grains are aggregates of the particles the shape and dimension of which are similar to those of the primary associated particles formed in PVB solution. © 1994 John Wiley & Sons. Inc.
Electron spin resonance study of γ‐irradiated poly(methacrylic acid)
Authors: Rao B. Sanjeeva , Hasan Mohd. Fasiul , Reddy N. Subbarami , Reddy Y. Sudarsana 
Published: April 2003

AbstractLow temperature relaxations in poly(methacrylic acid) (PMAA) have been studied by electron spin resonance (ESR) spectroscopy. The observed 8 line ESR spectra of irradiated PMAA in the temperature range 77‐300K (LNT‐RT) is attributed to the free radicals of the type ∼ CH2CHCH3. Assignment of ESR spectra to free radicals has been made on the basis of magnetic parameters employed to simulate ESR spectra at different temperatures. Further, ESR spectra below LNT have been simulated, using the set of parameters employed to simulate the experimental spectrum at LNT. Magnetic parameters of the ESR spectra at LNT and below LNT indicate γ‐ and δ‐relaxations of PMMA chains. © 1994 John Wiley & Sons, Inc.