bluuebunny/crossref_metadata_2025_split huggingface dataset:
Phase separation phenomena in solutions of poly(2,6‐dimethyl‐1,4‐phenylene oxide). IV. Thermodynamic parameters for solutions in a series of homologous solvents: Toluene to hexylbenzene
Authors: Koenhen D. M. , Bakker A. , Broens L. , Van den Berg J. W. A. , Smolders C. A. 
Published: April 2003

AbstractMelting‐point curves for solutions of poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) in a series of homologous solvents (toluene to n‐hexylbenzene) have been obtained from visual and differential scanning calorimetry measurements. The measured melting points were used to calculate thermodynamic interaction parameters. It was found that consistent values were obtained with the Flory–Hoffman melting‐point depression equation, if the assumption was made that solvent molecules are incorporated in the crystal lattice. To this end, an adapted dependence of the enthalpy of melting per polymer unit on the cocrystallizing solvent was used. The values of the thermodynamic interaction parameters in the series of solvents and their dependence on polymer weight fraction are explained qualitatively with simplified versions of equation‐of‐state theory and solubility parameter theory.
Comments on “some evidence against the existence of the liquid‐liquid transition. IV. The temperature dependence of shear viscosity”
Authors: Boyer Raymond F. 
Published: April 2003

AbstractA formal definition of TLL as a function of M̄n for polystyrene was prepared with literature TLL values from torsional braid analysis (TBA), differential scanning calorimetry (DSC), and zero‐shear melt viscosity η0. Data from six authors using anionically prepared PS and blends thereof were involved. The resultant linear least‐squares regression line, TLL(°C) = 148.5 − 11.487 × 104M̄ [standard error in TLL (calculated) 4.056 K, correlation coefficient R2 = 0.9534] is considered valid from M̄n = 2000 to the entanglement molecular weight Mc = 35,000. The “best” TLL values reported by Orbon and Plazek from double Arrhenius plots are well below this line for M̄v = 47,000, 16,400, 3400, and above it for M̄v = 1100. These best TLL values are artifacts arising from no or insufficient data points above or below TLL and/or too many data points near Tg. The associated high enthalpies of activation which they report confirm this diagnosis. The fact that these artificial TLL values tend to disappear when checked by the three‐parameter Vogel equation, logη = logA + B exp[(T − T∞)−1], has no relevance to the controversy concerning the existence and meaning of TLL. The claim by Orbon and Plazek that TLL values obtained by TBA, DSC, and melt viscosity are all artifacts of the individual methods by which they were obtained is inconsistent with the excellent master plot which they generate. Alternative plotting devices which reveal TLL > Tg from η0 vs. T−1 data, as developed by van Krevelen and Hoftyzer and by Utracki and Simha (not previously considered by either party), are reviewed. A statistical examination of the nature of the Vogel–Fulcher–Tammann–Hesse equation, based on synthetic data, is presented. Evidence for TLL in atactic polypropylene is offered based on published data by Plazek and Plazek. TLL is considered to possess both relaxational and quasiequilibrium attributes, just as Tg does.
Thermoplastic elastomers: Structural and morphological aspects of ether–esteramide copolymers
Authors: Cernia Enrico , D'ilario Lucio 
Published: April 2003

AbstractPolyesteramide 6NT6–polytetramethylene ether glycol (PTMEG) copolymers, precipitated from dilute solution, have been studied by small‐angle x‐ray scattering (SAXS) and wide‐angle x‐ray scattering (WAXS) with variation of the PTMEG content. A comparison of the structural characteristics of these materials has been made with those of the 6NT6 homopolymer. Chain folding is assumed as the crystallization mechanism for the low‐PTMEG‐content copolymers, with possible inclusion of polyether segments within the 6NT6 crystal lattice. WAXS data support the view of a weakening of the 6NT6 crystalline packing in the equatorial planes as the reason for broadening of the diffraction peaks, for changes in their relative intensities, and for the increase in the equatorial interplanar distances in the high‐PTMEG‐content samples. The annealing behavior has also been investigated.
Thermal behavior of the poly(2‐methoxy)‐Cyanurate of 1,1′‐bis(4‐hydroxy phenyl)‐Cyclohexane
Authors: Parsania P. H. , Patel K. C. , Patel R. D. 
Published: April 2003

AbstractThermal behavior of unfractionated poly(2‐methoxy)‐Cyanurate, PMCBC‐ film has been reported. The degradation of the polymer involved two steps. The glass transition temperature, Tg, from DSC and DMA studies is ∼ 200°C. TMA study shows that the glass‐rubber transition region is in the range of 157 to 199°C. The thermal stability of PMCBC has been found to be superior to commercially available polymers.
Drawing of poly(p‐phenylene sulfide) by solid‐state coextrusion
Authors: Ito Masayoshi , Porter Roger S. 
Published: April 2003

AbstractThe effects of drawing temperature on the physical and mechanical properties of poly(p‐phenylene sulfide) have been studied. A melt‐quenched film was drawn by solid‐state coextrusion both below (75°C) and above (95 and 110°C) the glass transition temperature Tg (85°C) of PPS. The maximum extrusion draw ratio (EDRmax) increased from 3.4 to 5.6 with increasing extrusion temperature Te from 75 to 110°C. It was found that extrusion drawing just above the Tg of PPS (95°C) produced more stress‐induced crystals. A high efficiency of draw in the amorphous region was achieved by extrusion at Te‐75°C. The tensile modulus at EDRmax decreased from 5.1 to 3.5 GPa with increasing Te from 75 to 110°C. The low efficiency of draw for the samples extruded at 110°C is explained in terms of disentanglement and chain slippage during drawing due to a less effective network.
Studies of solution dynamics of poly(N‐vinyl pyrrolidone) and its iodine adduct
Authors: Cheng H. N. , Smith T. E. , Vitus D. M. 
Published: April 2003

AbstractCarbon‐13 NMR spin‐lattice relaxation timesT1of poly(N‐vinyl pyrrolidone) (PVP) and PVP‐iodine have been studied in several solvents and at different temperatures. Three kinds of motion can be identified from theT1data: segmental motion, ring rotation, and ring puckering. The effective correlation time for segmental motion is calculated to be 1 × 10−9s, in good agreement with published proton NMR data. Another solvent, 1,1,2,2‐tetrachloroethane, behaves like D2O, the segmental correlation time being 3 × 10−9s. In benzene, however, the linewidths are very broad and tend to narrow with increasing temperature, but theT1s are not very different from those of PVP in D2O. The results suggest association of pyrrolidone rings in benzene that reduces chain dimensions and also restricts chain mobility. As for PVP‐iodine in water, again broad resonances are observed which sharpen considerably at higher temperatures. The result agrees with previous suggestions of specific interactions between the pyrrolidone group and iodine.
Low‐frequency Raman‐active modes and temperature dependences in oligo‐oxyethylene
Authors: Viras K. , King T. A. , Booth C. 
Published: April 2003

AbstractRaman spectra have been recorded for monodisperse and polydisperse samples of oligooxyethylene at several temperatures in the range 310–77 K. Four scattering peaks are found with frequency dependent on temperature. One at 92–80 cm−1 is unaffected by changes in chain length and is assigned to a lattice mode. The others are chain‐length dependent and are assigned either to the longitudinal acoustical modes (LAM‐1 and LAM‐3)or, less certainly, to a transverse acoustical mode.
Crystallization of bisphenol‐A polycarbonate induced by organic salts: Chemical modification of the polymer. III. Reaction mechanism
Authors: Bailly Ch. , Daumerie M. , Legras R. , Mercier J. P. 
Published: April 2003

AbstractIn the presence of a sodium arylcarboxylate or arylphenoxide, bisphenol‐A polycarbonate (PC) undergoes complex chemical modifications at high temperatures. The reaction mechanism is similar to the one previously established for model systems. Initially, the salt reacts with the carbonate groups of the polymer. This lowers the number‐average molecular weight and produces ionic chain ends of the phenoxide type. A fast transesterification reaction is then induced by a continuous exchange between the phenoxide and the carbonate groups, affecting the molecular distribution until an equilibrium is attained. In the presence of CO2, the phenoxide‐terminated PC undergoes further chemical modifications (formation of phenyl salicylate and phenyl phenoxybenzoate groups) leading to progressive crosslinking of the polymer.
Study of molecular mobility in ultraoriented polypropylene by the spin‐probe technique
Authors: Choy C. L. , Leung W. P. , Ma T. L. 
Published: April 2003

AbstractThe rotational mobility of nitroxide radicals in polypropylene samples with draw ratios varying from 1 to 18 has been studied between 30 and 110°C by the ESR technique. The drop in the rotational frequency with increasing orientation correlates very well with the behavior of various other measures of molecular mobility such as organic vapor sorption, proton spin–spin relaxation times from NMR, and dynamic mechanical loss factor. This implies that each of these parameters is a good indicator of the amount of free volume in the amorphous regions. Annealing at high temperature relaxes the amorphous chain segments, thereby increasing the spin‐probe rotational frequency in the drawn samples to values even higher than that in the quenched isotropic material.
Correction of the mark–houwink–sakurada equation in the low‐molecular‐weight range
Authors: Dondos A. , Skordilis V. 
Published: April 2003

AbstractA relation is proposed which gives the error in determination of molecular weights of polymer samples using the extrapolation of the Mark–Houwink–Sakurada equation into the low‐molecular‐weight region. The error is directly related to the exponent α of the Mark–Houwink–Sakurada equation and the relation is the same for a number of polymer + solvent systems.
Dilute‐solution properties of trans‐1,4‐polyisoprene
Authors: Chaturvedi P. N. , Patel C. K. 
Published: April 2003

AbstractTrans‐1,4‐polyisoprene was fractionated by both fractional precipitation and preparative gel permeation chromatography to obtain possibly sharp fractions of narrow molecular weight distribution. Selected fractions were characterized by light scattering, viscosity, and gel permeation chromatography. Necessary corrections for molecular heterogeneity were applied. Some of the characteristic relations between [η] and Mw are [η] = 1.81 × 10−4 M in benzene at 30°C, [η] = 1.38 × 10−4 M in n‐hexane at 30°C, which are found to be in good agreement with literature data when corrected for molecular heterogeneity.
Craze fibril structure and coalescence by low‐angle electron diffraction
Authors: Yang Arnold C.‐M. , Kramer Edward J. 
Published: April 2003

AbstractBrown has shown that low‐angle electron diffraction (LAED) may be used to determine fibril diameters D and spacings D0 of crazes in thin polymer films. He found, however, that the D and D0 determined for air crazes in polystyrene (PS) thin films were larger by about a factor of 3 than those in PS bulk crazes determined by using small‐angle x‐ray scattering (SAXS). We have repeated Brown's LAED experiments and find that the discrepancy may be caused by an aging effect. Our fresh crazes have D and D0 values from LAED that are comparable to those of bulk PS crazes determined by SAXS. As the craze ages, however, fibrils retract and coalesce in wide regions of the craze, leading eventually to an observable “skin.” Aged crazes thus have much larger D and D0 values than do fresh crazes. The large molecular mobility of the PS molecules in the fibrils necessary for this aging to occur at room temperature has important implications for fibril failure.
X‐ray scattering from the long spacing of completely crystalline oligoethylene glycol di‐n‐alkyl ethers
Authors: Swales Timothy G. E. , Domszy Roman C. , Beddoes Roy L. , Price Colin , Booth Colin 
Published: April 2003

AbstractCompletely crystalline samples of oligoethylene glycol di‐n‐alkyl ethers, H(CH2)nO‐(CH2CH2O)m(CH2)nH, where m is 9 or 15 and n is in the range 12‐18, were orientated in capillaries by slow crystallization in a temperature gradient. X‐ray scattering from the long spacings of the oriented samples, rotated continuously through 360°, was concentrated on the equator of a Debye–Scherrer photograph and many orders of reflection could be seen (e.g., up to order 30). The intensities of these reflections were analyzed by use of a model electron density distribution through the layer structure. Thus it was shown that the central oxyethylene block, in helical conformation, is oriented normal to the layer end plane, while the end alkyl bolcks, in planar zigzag conformation, are tilted relative to the layer end plane at an angle in the range 70°–64°.
Electrical properties of polyacetylene/polybutadiene blends
Authors: Sichel E. K. , Rubner M. F. 
Published: April 2003

AbstractMicrostructural Composites of polyacetylene/polybutadiene blends were prepared by polymerizing polyacetylene in a matrix of polybutadiene. The polyacetylene in the blends can be doped with iodine to produce electrically conducting composites. Thus a new material is formed which retains many of the electrical properties of doped polyacetylene but whose mechanical properties are different from those of either polyacetylene or polybutadiene.
Quantum yield for poly(methyl methacrylate) chain scission by 214–229 nm wavelength light
Authors: Shultz A. R. , Frank P. , Griffing B. F. , Young A. L. 
Published: April 2003

AbstractThe quantum yield for poly(methyl methacrylate)chain scission by ultraviolet light in the 214–229 nm wavelength region was found to be ϕd = 0.03 scissions per absorbed photon. Samples were 1.65‐μm films spun cast on silicon wafers and irradiated under flowing nitrogen by a cadmium vapor lamp. Gel permeation chromatography was used for molecular weight determination. Heating (postbaking) the irradiated films at 150°C for one hour under reduced‐pressure flowing nitrogen increased the observed scissions per absorbed photon to 0.04. Glass transition temperatures by DSC are well‐represented by Tg (K) = 393.3 − 2.0 × 105/Mn for the postbaked samples (139,000 > Mn > 6500).
Polyethylene fiber formation in tubular flow. II. Discussion of precursor formation and nucleation time analysis
Authors: Mchugh A. J. , Rietveld J. 
Published: April 2003

AbstractThis is a continuation of the preceeding paper, Part I, and presents a discussion of the nature of the precursor structure formation process observed in the flow‐induced crystallization experiments described in I. A discussion of stress‐induced crystallization theory as applied to these experiments is also given and a first‐order analysis of crystal nucleation rates is presented. Conclusions regarding the nature of flow‐induced crystallization and our current ability to quantitatively model the overall process are also presented.
Rheo‐optical fourier‐transform infrared spectroscopy of polymers. 9. Stretching‐induced II(α)‐I(β) crystal phase transformation in poly(vinylidene fluoride)
Authors: Siesler H. W. 
Published: April 2003

AbstractSimultaneous Fourier‐transform infrared (FTIR) spectroscopic and stress‐strain measurements have been used to study the II(α)‐I(β) crystal phase transformation in poly(vinylidene fluoride) under tensile stress at variable temperature. From the experimental data it can be derived that in the investigated temperature interval from 348 to 423 K the drawing process is inhomogeneous and occurs via formation of a neck. The II(α)‐I(β) phase transformation is restricted to temperatures below 423 K and its onset is generally related to the formation of the neck.
Translational diffusion of polystyrene in cyclohexane at infinite dilution from 283 to 348 K
Authors: Barooah A. , Chen S. H. 
Published: April 2003

AbstractThe translational diffusion coefficients are reported for polystyrenes with molecular weights 2000, 4000, and 9000 in cyclohexane at infinite dilution from 283.2 to 348.2 K. The results suggest that the hydrodynamic radii stay constant to within ±3% and that the real chain for molecular weight 9000 at 308.2 K is well represented by a Gaussian or Monte Carlo model involving the idea of statistical steps. Furthermore, the success of Hildebrand's free‐volume empiricism has led to a correlation between Dμ0/T and M which represents the observed diffusivities to within ±2%.
Evaluation of theories for diffusion in polymer–solvent systems
Authors: Vrentas J. S. , Duda J. L. , Hou A.‐C. 
Published: April 2003

AbstractA method is proposed for examining differences in the predictive capabilities of three versions of the free‐volume theory of polymer—solvent diffusion using only a small amount of diffusivity data. The utility of the method is illustrated using a limited diffusivity data set for the methanol‐poly(vinyl acetate) system.
An x‐ray diffraction study of nonlinear polyethylene. II. Small‐angle scattering observations near the melting point
Authors: Vonk C. G. , Koga Y. 
Published: April 2003

AbstractA method is presented for obtaining from the zeroth‐order peak in small‐angle x‐ray scattering (SAXS) patterns the weight average of the thickness C of crystalline lamellae in polymers close to the melting point. The method fails if a first‐order peak can be discerned to be superimposed on the zeroth‐order peak. The method was applied, together with the one described in Part I of this series for obtaining the number average of C, to three polyethylene samples of different side‐group content which were heated to temperatures close to the melting point. While heating always causes an increasing number of lamellae to melt, a linear sample also shows pronounced thickening of the remaining lamellae. This effect, however, decreases with increasing side‐group content, and is virtually absent in a vinyl acetate copolymer containing 53 side groups per 1000 C atoms. A qualitative explanation for the role of the side groups in limiting the crystal thickening processes is put forward. By comparing results obtained after isothermal annealing and during isothermal crystallization from the melt it is concluded that at temperatures close to the melting point the polymers approach a final state which no longer depends on the thermal history of the sample.
Light‐scattering characterization of poly(ethylene terephthalate)
Authors: Naoki Motosuke , Park Il‐Hyun , Wunder Stephanie L. , Chu Benjamin 
Published: April 2003

AbstractBy using a closed‐circuit filtration system, we have succeeded in clarifying poly(ethylene terephthalate) (PET) dissolved in hexafluoroisopropanol (HFIP). Such static properties as the radius of gyration Rg, the weight‐average molecular weight Mw, and the second virial coefficient A2 and such dynamic properties as the translational diffusion coefficient D, or its equivalent hydrodynamic radius Rh, and the second (diffusion) virial coefficient kd were determined for several PET samples of different molecular weights by using light‐scattering intensity and linewidth measurements. An empirical relation between Do (or Rh) and Mw was established: Rh = (1.77±0.15)X10−2 M with Rh and Mw expressed in units of nanometers and grams per mole, respectively. The empirical exponent αD(ca. 0.58±0.01) is in good agreement with the less precisely determined intrinsic viscosity/molecular weight exponent αη (ca. 0.71±0.02). Several intensity correlation functions were measured very precisely using long accumulation times. A Laplace inversion was performed using the singular‐value decomposition technique. The approximate molecular weight distribution (MWD) determined by light‐scattering spectroscopy was in reasonable agreement with a completely independent determination of MWD using gel permeation chromatography (GPC). It was interesting to note, though not surprising, that GPC showed emphasis on lower‐molecular‐weight fractions, while light‐scattering emphasized higher‐molecular‐weight fractions. The agreement further strengthens some complementary aspects of the two techniques.
Left–right and dynamic correlation
Authors: Molawi Kian , Cohen Aron J. , Handy Nicholas C. 
Published: April 2003

AbstractWithin density functional theory, it is natural to separate the correlation energy into two parts: left–right correlation and dynamic correlation. Left–right correlation arises from the exchange part of functionals, and dynamic correlation arises from the correlation part of functionals. We examine the nature of these correlation energies as molecules are distorted. We observe that such a natural separation is not possible using the methods of quantum chemistry. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002
An illness–death stochastic model in the analysis of longitudinal dementia data
Authors: Harezlak Jaroslaw , Gao Sujuan , Hui Siu L. 
Published: April 2003

AbstractA significant source of missing data in longitudinal epidemiological studies on elderly individuals is death. Subjects in large scale community‐based longitudinal dementia studies are usually evaluated for disease status in study waves, not under continuous surveillance as in traditional cohort studies. Therefore, for the deceased subjects, disease status prior to death cannot be ascertained. Statistical methods assuming deceased subjects to be missing at random may not be realistic in dementia studies and may lead to biased results. We propose a stochastic model approach to simultaneously estimate disease incidence and mortality rates. We set up a Markov chain model consisting of three states, non‐diseased, diseased and dead, and estimate the transition hazard parameters using the maximum likelihood approach. Simulation results are presented indicating adequate performance of the proposed approach. Copyright © 2003 John Wiley & Sons, Ltd.
Generating test data from state‐based specifications
Authors: Offutt Jeff , Liu Shaoying , Abdurazik Aynur , Ammann Paul 
Published: April 2003

AbstractAlthough the majority of software testing in industry is conducted at the system level, most formal research has focused on the unit level. As a result, most system‐level testing techniques are only described informally. This paper presents formal testing criteria for system level testing that are based on formal specifications of the software. Software testing can only be formalized and quantified when a solid basis for test generation can be defined. Formal specifications represent a significant opportunity for testing because they precisely describe what functions the software is supposed to provide in a form that can be automatically manipulated.This paper presents general criteria for generating test inputs from state‐based specifications. The criteria include techniques for generating tests at several levels of abstraction for specifications (transition predicates, transitions, pairs of transitions and sequences of transitions). These techniques provide coverage criteria that are based on the specifications and are made up of several parts, including test prefixes that contain inputs necessary to put the software into the appropriate state for the test values. The test generation process includes several steps for transforming specifications to tests. These criteria have been applied to a case study to compare their ability to detect seeded faults. Copyright © 2003 John Wiley & Sons, Ltd.