bluuebunny/crossref_metadata_2025_split huggingface dataset:
C‐13 NMR analysis of polystyrene from low‐molecular‐weight model compounds
Authors: Sato Hisaya , Tanaka Yasuyuki , Hatada Koichi 
Published: April 2003

AbstractMethylene and phenyl C1 carbon signals of polystyrene are assigned on the basis of the signal assignments of styrene oligomers. Polystyrenes prepared with benzoyl peroxide, n‐butyllithium, and trifluoroboron etherate catalysts have random distributions with probabilities of racemic dyads of 0.54, 0.56, and 0.45, respectively.
An inverse gas‐chromatographic study of the interaction of water with some cellulose derivatives
Authors: Aspler J. S. , Gray D. G. 
Published: April 2003

AbstractThe sorption isotherms for water on cellulose triacetate, cellulose acetate (degree of substitution 2.45), cellulose monoacetate (degree of substitution 0.89), and ethyl cellulose were measured by finite‐concentration inverse gas chromatography. The isotherms for cellulose monoacetate were also measured with a vacuum microbalance. Polymer–solvent interaction parameters and partial molar heats of sorption at zero concentration of water were estimated from the extrapolated data, but kinetic effects and isotherm curvature lowered the precision of these results. The water sorption isotherms were examined according to the Zimm cluster theory, and the results were compared to those for cellulose and (hydroxypropyl)cellulose.
Chain orientation in polystyrene/poly(2,6‐dimethyl‐1,4‐phenylene oxide) blends
Authors: Wang L. H. , Porter Roger S. 
Published: April 2003

AbstractThe differential orientation of polymer chains has been measured in polystyrene (PS)/poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) compatible blends. Density measurements are reported as a function of binary blend composition at 23°C. Drawing was performed by solid‐state coextrusion. PS/PPO blend compositions of 90/10 and 75/25 were drawn within sandwiches of polyethylene at 145°C and isotactic polypropylene at 155°C, i.e. at ca. 25°C above the glass transition temperatures of the two blends. The change in Fourier‐transform infrared dichroisms on drawing these blends was measured at 906 and 1190 cm−1, corresponding to predominantly PS and PPO, respectively. The orientation of PS and PPO was observed as a function of draw ratio λ in the range 1–5; orientations increased with λ for both PS and PPO in both blends but to different degrees. Both polymers decreased in orientation with increasing PPO content. Annealing with fixed ends showed that the PPO chains disorient more slowly than those of PS. All binary systems were found to be amorphous and compatible.
A 13C NMR study of mesomorphic solutions of poly(p‐phenylene terephthalamide)
Authors: Close L. G. , Fornes R. E. , Gilbert R. D. 
Published: April 2003

AbstractSolutions of poly(p‐phenylene terephthalamide) in fuming sulfuric acid were characterized by 13C NMR spectroscopy and solution viscosity measurements over the 2–28% w/w concentration range. The spectra showed the presence of two distinct amide carbonyl resonances at low concentration, tentatively assigned to cis and trans conformations. As the concentration increased, additional carbonyl lines were observed along with significant broadening. Peak area measurements showed that only the polymer molecules in the isotropic environments contributed to the 13C NMR spectra and a considerable amount of the polymer remained in the isotropic phase at concentrations previously considered to consist of polymer in highly anisotropic regions. Spin‐lattice relaxation times were measured at six concentrations using the inversion recovery method. The aromatic carbons relaxed at a much faster rate (ca. 0.10 s) than the carbonyls (ca. 0.45 s), but the relaxation rates for both carbons were essentially constant over the concentration range, indicating that the observed isotropic phase is not affected by changes in the macroscopic solution behavior so as to alter spin‐lattice relaxation mechanisms.
Determination of long‐chain branching in model polystyrene samples by the GPC‐sedimentation method
Authors: Tung L. H. , Gatzke A. L. 
Published: April 2003

AbstractThe GPC–sedimentation velocity method proposed earlier for the determination of long‐chain branches was examined quantitatively by using model star‐shaped and comb‐shaped polystyrene samples of known degree of branching. The results showed that separation by sedimentation velocity was more sensitive to branching variations than separation by GPC. The results showed also that at low and moderate levels of branching the GPC–sedimentation velocity method reflected accurately the amounts of branching in the model samples. At high levels of branching, the method underestimated the amount of branching. The discrepancy, however, appears to have been caused by the inadequacy of the theories used in the interpretation of the raw data and not by any inherent problem in the method itself. The relative sensitivities of the GPC‐sedimentation, GPC‐viscosity, and GPC–light scattering methods are discussed.
Thermotropic homopolyesters. III. Preparation and properties of polymers based on 4′‐hydroxyphenyl‐4‐hydroxycinnamate
Authors: Krigbaum W. R. , Ishikawa T. , Watanabe J. , Toriumi H. , Kubota K. , Preston J. 
Published: April 2003

AbstractLow‐molecular‐weight 4′‐acetoxyphenyl‐4‐acetoxyoinnamate, as well as several polyesters synthesized from this monomer and aliphatic dibasic acids, exhibit thermotropic nematic phases. DSC heating curves for all of the polymers exhibit multiple transitions. The amount of crystallinity of these polymers at room temperature is small and the degree of order along the chain axis in the crystalline phase is poor. For the lower homologues the nematic phase exists over a broad temperature range of approximately 100°C. The polyester from chiral (+)‐3‐methyl adipate forms a thermotropic cholesteric phase. Both the diacetoxy monomer and azelate polymers of low molecular weight adopt the homeotropic texture on glass slides, but with increasing molecular weight the planar texture becomes preferred. Investigation of the effects of electric fields in the conduction regime upon the nematic phase of the diacetoxy monomer revealed that Williams domains are formed only with difficulty. In most cases, a stationary pattern appeared instead. At higher voltage the dynamic scattering mode (DSM) was obtained, and above this a field‐induced transition to the isotropic phase. The azelate polyesters exhibited Williams domains and the DSM in the conduction regime. The formation time for Williams domains was fairly short for polymers having ηinh < 0.44 dL/g, but increased to 80 min when ηinh = 0.68 dL/g. The DSM was only observed for polymers having ηinh < 0.61 dL/g. For these polymers the critical frequency separating the conduction and dielectric regimes exhibits a stronger temperature dependence than that of low‐molecular‐weight nematogens. A new instability pattern is reported for the azelate polyesters in the dielectric regime.
Pressure dependence of the viscosity of dilute polystyrene solutions in toluene
Authors: Claesson Stig , McAtee James L. , Ali Sabz 
Published: April 2003

AbstractThe effect of pressure on the viscosity of dilute solutions of anionically polymerized polystyrene (M̄w = 209,000; Mw/Mn = 1.12) in toluene has been studied at different temperatures and concentrations using a falling‐body viscometer. Measurements were performed in the concentration range from 0.0025 to 0.02 g/mL and at temperatures from 25 to 45°C under pressure up to 1057 bars. The viscosity coefficient η increases exponentially with pressure at a given temperature and concentration, while the apparent volume of activation V‡ decreases with increasing temperature. The hypothesis that the pressure dependence of η is given by the pressure dependence of the activation energy holds true under the prevailing thermodynamic conditions. Log η increases linearly with increasing concentration at a given pressure. Intrinsic viscosity increases with increasing pressure, whereas the Huggins constant decreases.
Light‐scattering photography of polymers near the glass transition
Authors: Carroll P. J. , Patterson G. D. , Cullerton S. A. 
Published: April 2003

AbstractLaser light scattered from a block of polystyrene is observed to have a pattern of bright and dark regions called speckle. We observe that the speckle pattern has a lifetime consistent with that of the average relaxation lifetime 〈τ〉 of the intensity fluctuations of the medium as determined by photon correlation spectroscopy. In order to study the pattern of the scattered light, a series of photographs was taken at a variety of exposure times. For each series, the value of the average relaxation lifetime is defined by the temperature and pressure of the polystyrene sample. When the value of 〈τ〉 is short relative to the exposure time, the photograph displays only a random pattern of exposed grains. This is due to the large number of fluctuations that have occurred during the exposure time with random phases relative to one another. As the average relaxation time is increased at a constant exposure time, the speckle pattern appears when the value of 〈τ〉 becomes comparable to the exposure time. The phenomenon of laser speckle allows the time scale of the slowly relaxing fluctuations near the glass transition to be visualized. A digitized series of such pictures could be analyzed to obtain the average relaxation time for the fluctuations, just as in normal photon correlation spectroscopy where the intensity of one coherence area is measured as a function of time.
Photon correlation spectroscopy of polymers in the glassy state
Authors: Patterson G. D. , Carroll P. J. 
Published: April 2003

AbstractPhoton correlation spectroscopy has proven to be a very useful technique for studying slowly relaxing density and optical anisotropy fluctuations in bulk polymers near the glass transition. When some of the fluctuations achieve relaxation times much longer than the typical averaging time for the intensity autocorrelation function (104 s), the result must be treated in the partially heterodyned limit. Also, when the sample is near the glass transition but not at equilibrium the correlation function is not stationary in time because the system is relaxing as a whole toward the equilibrium state. The above effects are discussed theoretically and demonstrated experimentally in polystyrene as a function of temperature and pressure. Light scattering with coherent excitation also fluctuates in space as well as in time (as shown in the accompanying paper). The consequences of this effect are discussed. When most of the intensity is associated with fluctuations whose relaxation times are very long in polystyrene, there is still a broad relaxation function evident. This is characteristic of a secondary relaxation process.
An analysis of the reflective component of small‐angle X‐ray scattering patterns from crazed polystyrene
Authors: Westbrook P. A. , Fellers J. F. , Cakmak M. , Lin J. S. , Hendricks R. W. 
Published: April 2003

AbstractAn investigation of the reflective component of small‐angle x‐ray scattering patterns of polystyrene crazes is performed. It is shown that the strong streak parallel to the tensile axis consists predominantly of reflected radiation, while the remaining pattern is composed entirely of diffracted radiation. X‐ray reflection off unparallel regions of crazes is discussed and the nature of the reflection is also considered in terms of collimation quality. An analysis methodology based on craze tip angular distribution is proposed.
The use of model networks with reptating chains to study extraction efficiencies
Authors: Mark J. E. , Zhang Z.‐M. 
Published: April 2003

AbstractIt is possible to prepare “model” elastomeric networks having known values of the molecular weight Mc between crosslinks by endlinking functionally terminated polymer chains having number‐average molecular weights Mn equal to the desired values of Mc. If chains having chemically inert groups at both ends are intentionally included during the preparation of such a system, they will remain unattached, merely reptating through the subsequently formed network structure. This technique was used to prepare a series of tetrafunctional polydimethylsiloxane (PDMS) networks having essentially the same degree of crosslinking (10−3Mc = 11.3 g mol−1) and constant amount of diluent in the form of unattached PDMS chains having molecular weights of 10−3Md = 26.4, 18.6, 15.8, 9.8, 6.7, 1.2, and 0.70 g mol−1. Because of the very high mobility of PDMS, it was also possible to introduce essentially the same amount of the same diluents into already formed PDMS networks having the same Mc. Extractions carried out using tetrahydrofuran at room temperature showed that the diluent (“sol fraction”) introduced by swelling the network is more easily removed than that present during the endlinking, possibly because of less convoluted arrangements within the network structure. Chains with the largest values of Md which were present during the endlinking were found to be very difficult to remove entirely. It is therefore extremely important to carry out exhaustive extractions to obtain reliable values of network sol fractions, particularly when such data are to be used to estimate extents of reaction in the preparation of end‐linked elastomers.
A fluorescence polarization study of the effect of matrix molecular weight on the relaxation of a labeled molecule in a stretched polymer melt
Authors: Tassin J. F. , Monnerie L. 
Published: April 2003

AbstractFluorescence polarization has been used to measure the orientation during stretching of a polystyrene chain embedded in a matrix of narrow‐dispersion polystyrene chains of a different molecular weight and labeled by an anthracene group covalently bound at the middle of a chain. Strong coupling between the relaxation of the labeled chain and the matrix chains is evidenced, the orientation of the labeled chain being partially governed by the molecular weight of the matrix. This behavior is interpreted qualitatively on the basis of a molecular model showing that the relaxation of a polymer chain is strongly affected by the entanglements acting on the chain, the number of which is also related to the motion of the surroundings. Good agreement is found between experimental data and the behavior predicted by the model.
Polymer–polymer interaction parameters of polystyrene and polybutadiene from studies in solutions of toluene or tetrahydrofuran
Authors: Narasimhan Venkataraman , Huang Robert Y. M. , Burns Charles M. 
Published: April 2003

AbstractEquations used for the determination of polymer–polymer interaction parameters for narrow molecular weight distribution polymers which have undergone phase separation in solutions are discussed. Binodals with tie lines and plait points are presented for ternary systems polystyrene‐polybutadiene‐toluene and polystyrene‐polybutadiene‐tetrahydrofuran. Typical interaction parameters determined from the experimental data for the polystyrene‐polybutadiene systems are presented.
Cage effects in recombination of allyl radicals in irradiated polyethylene. II. Cumulative reaction rates and decay kinetic processes
Authors: Hwang Lian‐Pin 
Published: April 2003

AbstractHwang and Cheng have studied the recombination reaction of allyl radicals in irradiated polyethylene by including the effects of (i) diffusion of macroradicals by jumps of finite size in the crystalline phase and (ii) a caging reaction with a finite rate in the disordered region. In this work their results are used to analyze cumulative reaction rate data on the decay of allyl radicals in extended‐chain and Marlex film polyethylene. The kinetic parameters obtained show the effects of reaction temperature, irradiation dose, and morphological differences.
ESR study of the diacetylene polymer 4BCMU
Authors: Freitas J. A. , Greenbaum S. G. 
Published: April 2003

AbstractElectron Spin Resonance (ESR) measurements of the polydiacetylene 4BCMU in the solid‐state indicate the presence of a thermally activated paramagnetic center with g ≈ 2.002 and first‐derivative peak‐to‐peak linewidth of ≈ 17G. An abrupt and irreversible decrease in ESR signal intensity is observed at ca. 400 K, and appears to be associated with the solid‐state planar‐nonplanar conformational transformation manifested by an irreversible color change from metallic brown to red.
The effect of temperature on the infrared spectra of poly(ethylene terephthalate)
Authors: Lin Shaow‐Burn , Koenig Jack L. 
Published: April 2003

AbstractReversible and irreversible spectral changes are observed on heating of solvent‐cast films of poly(ethylene terephthalate) (PET) between 30 and 230°C. The irreversible changes are due to the gauche‐trans isomerization of the ethylene glycol segments and the corresponding changes in the symmetry and resonance characteristics of the aromatic rings. On the other hand, there are thermally reversible spectral changes. These reversible effects are primarily observed for the modes of the aromatic ring and the trans ethylene glycol segment. These reversible spectral changes include intensity variations and frequency shifts and are found to be linearly dependent on the measurement temperature. These reversible changes arise from changes in intermolecular and intramolecular forces as the temperature changes.
Nonlinear viscoelasticity of entangled polymer chains. II. Comparison of the slip‐link model with stress measurements at constant rate of elongation on narrow‐distribution polystyrenes
Authors: Tassin J. F. , Thirion P. , Monnerie L. 
Published: April 2003

AbstractStress measurements have been performed at constant‐strain‐rate stretching of narrow distribution polystyrenes with various molecular weights elongated up to 300% at about 30°C above the glass transition temperature. The experimental stress‐strain curves are compared with those calculated on the basis of a new treatment of Doi's molecular model (Part I). Satisfactory agreement is obtained, leading to a rather precise estimate of the equilibration time. The latter has a theoretical dependence on the square of molecular weight.
A flow visualization technique for the determination of velocity profiles in dies with circular cross sections
Authors: Crater Davis H. , Cuculo John A. 
Published: April 2003

AbstractA unique retainer/transparent quartz die assembly was designed and fabricated to fit on a melt extruder. It permitted visualization of polymer flow behavior during melt spinning. Tracer particles were mixed with polymer chips prior to extrusion. A laser beam was directed through a lens system and used to illuminate the tracer particles in the melt only in a thin, vertical cross section of the transparent quartz die. Streak photography was used to determine the cross‐sectional velocity distribution of the melt as it passed through the die.
Matrix polymerization on polycationic backbones: A continuous method for following the polymerization kinetics
Authors: Blumstein A. , Milas M. , Ozcayir Y. , Bellantoni E. 
Published: April 2003

AbstractA novel method of following polymerization kinetics in dilute solutions of ionic monomers is described. The method, based on conductimetry, is very well adapted to follow polymerization of ionic species in very dilute solutions, in micellar solutions, or at interfaces, i.e., in all systems in which the polymerization process involves a shift in ionic equilibria. The method is applied to matrix polymerization of p‐styrene sulfonate–(2,2,2)4‐ionene complex and yields results in full agreement with the standard spectroscopic method frequently used in such systems. The conversion curves obtained by conductimetry are satisfactorily explained by Manning's ion condensation model and are in agreement with a previously proposed mechanism, based on ion condensation theory, for matrix polymerization of ionized monomers on polyelectrolytes.
A visualization study of poly(ethylene terephthalate) flow using potential chain‐ordering die geometries
Authors: Crater Davis H. , Cuculo John A. 
Published: April 2003

AbstractStreak‐photographic and stress birefringence techniques were used to analyze the flow of poly(ethylene terephthalate) through potential chain‐ordering die geometries. The streak photographs were used to determine velocity distributions and streamlines in various convergent dies. The different contours were seen to have a significant effect on the polymer streamlines and velocity distributions. The measured velocities were used to develop empirical equations, specific for each geometry, which relate velocity to position within the die and to throughput rate. Flow birefringence was used to determine the extent of molecular ordering. The optimum chain‐ordering die geometry was determined to be one which included a rapid initial decrease in cross‐sectional area. Birefringence was also used to monitor polymer flow instability. An unusual mechanism for instability was observed at intermediate throughput rates.
Effect of copolymerization and heat treatment on the structure and x‐ray diffraction of polyacrylonitrile
Authors: Gupta A. K. , Singhal R. P. 
Published: April 2003

AbstractWide‐angle x‐ray diffraction studies are reported on polyacrylonitrile (PAN) (homopolymer powder and fiber samples) and its random copolymers with methyl methacrylate (MMA) and methacrylonitrile (MAN). A new method of determination of degree of order which involves resolution of the individual maxima in the diffraction pattern is described and compared with the methods used in the literature. Comparison of the results on untreated fibers with those on untreated homopolymer powder samples, and the effect of heat treatment, suggest the molecular rod conformation of the PAN molecules in the amorphous phase. Heat treatment or the orientation induces a parallel alignment of the molecular rods in the amorphous phase, similar to the cyrstalline structure of PAN. Copolymerization with both the comonomers MMA and MAN produces qualitatively similar effect on the structure of PAN, which depends on the comonomer content. Below a critical comonomer content c* (c* = 12 mol % for MMA and 25 mol % for MAN comonomer), the crystalline lattice remains that characteristic of PAN, whereas above the critical comonomer content some modification in the crystalline lattice is apparent.
Fourier‐transform infrared study of conformational changes in plasticized poly(vinyl chloride)
Authors: Theodorou M. , Jasse B. 
Published: April 2003

AbstractFourier‐transform infrared spectroscopy has been used for the detection of conformational changes induced by plasticization in atactic poly(vinyl chloride) (PVC). The amount of short trans syndiotactic sequences decrease upon plasticization. This change depends on the amount and kind of plasticizer. Difference spectra emphasize changes in the distribution of gauche defects in the chains as a function of temperature in plasticized PVC films.
Thermodynamic properties of a small droplet of water around an ion in a compressible matrix
Authors: Dreyfus Bernard 
Published: April 2003

AbstractA model is presented for the adsorption of water by ions in a deformable matrix. Only two opposing “effects” are included. The first is the mechanical resistance of the matrix to deformation which is treated within the framework of linear elasticity extended to the case of large deformations. The other effect is of electrical origin which is shown to be much more important than the purely entropic osmotic pressure. In the model only one immobile ion located at the center of a spherical droplet of water is considered. It is shown that the result does not significantly depend upon the dielectric constant of water, provided it is much larger than that of the matrix. The thermodynamic relations reveal that in fact most of the properties of the system depend mostly on the dielectric and elastic coefficients of the matrix. This simplified model should be considered as a guide for the understanding of the behavior of such systems rather than as a precise description of real materials. Some quantitative comparisons are made with a few experimental results.