bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dispersion polymerization of styrene in ethanol: Monomer partitioning behavior and locus of polymerization
Authors: Lu Y. Y. , El‐Aasser M. S. , Vanderhoff J. W. 
Published: April 2003

AbstractA thermodynamic model has been proposed for the simulation of monomer partitioning behavior in the dispersion polymerization of styrene in ethanol. The monomer concentration in the polymer particles is very low (20 vol% at 5% conversion) and decreases further as the polymerization proceeds. It is independent of stabilizer concentration but is strongly dependent on initial monomer concentration. The partitio
n coefficient ([Mp]/[Mc]) of styrene increases from 0.8 to 1.1 with incresing conversion. There are two polymerization loci in dispersion polymerization, namely the continuous and polymer phases. Competition between solution and heterogeneous polymerization has been observed in this system. The rate of dispersion polymerization is dependent on initial monomer concentration but is independent of initiator concentration at higher conversions. The molecular weight of the polymers produced by this process increases with increasing conversion and decreases with increasing initiator concentration.
Ionic products in ground polymer. IV. Anions in poly(vinylidene fluoride)
Authors: Sakaguchi Masato , Kinpara Hiromu , Hori Yasuro , Shimada Shigetaka , Kashiwabara Hisatsugu 
Published: April 2003

AbstractWhen poly(vinylidene fluoride) (PVDF) was ground with tetracyanoethylene (TCNE) powder in a vibration glass ball mill in vacuum in the dark at 77 K, the TCNE anion radical (TCNE‐) was detected in the mixture by ESR spectroscopy. The TCNE.‐ is formed by the abstraction of electrons by TCNE from the anion that is produced by a heterogeneous bond scission of carbon‐carbon bonds in the polymer main chain. The assignment of TCNE.‐ was carried out by the ESR spectral simulation on the basis of an anisotropic effective hyperfine tensor that includes a forbidden transition term. At least 85% of the bond scission of the PVDF main chain is induced by a heterogeneous process to produce ionic products. The yield of these mechanions seems to increase with the polarity of carbon‐carbon bond owing to a substituent group bonded to the carbon in the polymer main chain.
Miniemulsion copolymerization of vinyl acetate and butyl acrylate. II. Mathematical model for the monomer transport
Authors: Delgado Joaquin , El‐Aasser Mohamed S. , Silebi Cesar A. , Vanderhoff John W. , Guillot Jean 
Published: April 2003

AbstractA mathematical model is presented to describe the monomer transport between monomer droplets, aqueous phase, and polymer particles during the course of an emulsion polymerization. The model was used to investigate the role of the cosurfactant (hexadecane) in the miniemulsion copolymerization of 50:50 molar ratio vinyl acetate‐butyl acrylate monomer mixture, as well as the effect of the different components and process variables on the rate of copolymerization, monomer distribution between phases, and composition of the copolymer.
A technique for measuring the crosslink densities in both phases of a vulcanizate blend
Authors: Honiball D. , Mcgill W. J. 
Published: April 2003

AbstractThe magnitude of the depression of the freezing point of a solvent in a swollen vulcanizate is dependent on the crosslink density. It is shown that use of such measurements, coupled with the conventional swelling technique, allows the crosslink density in both phases of a vulcanized blend to be determined.
Mechanical anisotropy in rolled nylon 66
Authors: Choy C. L. , Leung W. P. , Ong E. L. , Wang Yimin 
Published: April 2003

AbstractThe nine independent stiffness constants Cpq for rolled nylon 66 at thickness reduction ratios λt = 2.4, 4.9, 7.6 have been measured from −40 to 50°C by an ultrasonic method at 10 MHz. Analysis of x‐ray pole figures indicates that at high λt the material has a uniplanar‐axial texture, with hydrogen‐bonded (010) planes parallel to the roll plane and the molecular chains along the roll direction. The mechanical behavior is determined not only by the alignment of molecular chains and hydrogen bonds but also by the microfibrillar morphology. On the basis of this idea the magnitudes of the tensile moduli along the three principal axes can be understood in terms of the Takayanagi model. The effects of water absorption have also been investigated.
The dielectric properties of liquid‐crystal random copolyesters of 4‐hydroxybenzoic acid and 2‐hydroxy 6‐naphthoic acid
Authors: Alhaj‐Mohammed M. H. , Davies G. R. , Jawad S. Abdul , Ward I. M. 
Published: April 2003

AbstractDielectric measurments made from 1 Hz to 10 kHz and from ‐80 to 150°C on random copolyesters of 4‐hydroxybenzoic acid (HBA) and 2‐hydroxy 6‐naphthoic acid (HNA) reveal three relaxation processes at low frequencies rather than the two seen at audio frequencies. The higher temperature α process is similar to a glass transition, with a high activation energy ∼ 170 kcal/mol, but the two lower temperature processes are identified as local mode processes associated with the HNA and HBA moieties, respectively. It is shown that the observed value of the permittivity above the glass transition is lower than that which would be expected for ester groups rotating freely about the local chain axis, and it is suggested that this may be due to several factors including immobilization of dipoles in the crystalline regions, correlated motion of dipoles, and librational rather than rotational motion.
Cooperative chain relaxation in miscible polymer blends
Authors: Saito Hiromu , Takahashi Mamoru , Inoue Takashi 
Published: April 2003

AbstractOrientation relaxation of dissimilar chains in the molten miscible blends, poly(methyl methacrylate)/poly(vinylidene fluoride) and poly(methyl methacrylate)/poly(vinylidene fluoride‐co‐trifluoroethylene), were investigated by measuring (1) the change of infrared dichroic ratio with time after the uniaxial stretching of film specimens, (2) the shear stress relaxation spectrum, and (3) birefringence relaxation in shear. The dissimilar polymers showed an identical time variation of the normalized Hermans orientation function. The blend showed a relaxation spectrum with a single characteristic relaxation time τc, depending on the blend composition. The birefringence relaxed monotonically, remaining positive. These results suggest that the dissimilar polymers do not relax independently but cooperatively. This behavior may be induced by a constraint due to the specific interactions between the dissimilar polymers, e.g., weak hydrogen bonding. For the cooperative chain relaxation, a third power relationship was found; τc/τe vprop; (M/Me),3 where τe and Me are the relaxation time and molecular weight of entanglement strand, respectively, and M is the number average molecular weight in the blend.
On the rheology of cold drawing. I. Elastic materials
Authors: Coleman Bernard D. , Newman Daniel C. 
Published: April 2003

AbstractIn this, the first paper in a series on neck formation and steady‐state drawing of polymeric fibers and films under uniaxial tension, the emphasis is laid on those aspects of the mechanics of cold drawing that are not sensitive to viscoelastic effects and, therefore, can be treated by use of constitutive assumptions appropriate to elastic materials. It is here shown that a unidimensional theory which has been employed to model the mechanics of slender bars in tension6 can be derived as an approximation for three‐dimensional bars and, in a sense which can be made precise, is valid to within an error of the order of the fourth power of the thickness. A particular constitutive equation for incompressible, three‐dimensional, elastic materials is explored in detail and is found to yield, for such slender bars as thin fibers and wide (but thin) strips of film, equations of equilibrium whose solutions are in good qualitative accordance with the necks and drawing configurations observed in practice.
Aging phenomena in isotactic polypropylene drawn at different temperatures
Authors: de Candia F. , Russo R. , Tidjani A. , Vittoria V. , Peterlin A. 
Published: April 2003

AbstractFibers of isotactic polypropylene drawn at different temperatures show aging phenomena after drawing. In particular a modulus stiffening is observed at room temperature where the modulus increases with the aging time. In the same time scale the birefringence is constant, while drastic effects on the transport properties are observed. The aging phenomenon can be explained in terms of two mechanisms: a secondary crystallization and/or a densification of the amorphous component.
Molecular modeling of polymers. IV. Estimation of glass transition temperatures
Authors: Hopfinger A. J. , Koehler M. G. , Pearlstein R. A. , Tripathy S. K. 
Published: April 2003

AbstractA method is described which allows molecular modeling to be combined with a group additive property model to estimate glass transition temperatures of linear polymers. Tg is assumed to be a function of conformational entropy and mass moments of the polymer. These two molecular properties are estimated in terms of the torsion angle units composing the polymer using conformational energy calculations. A “universal” Tg equation is derived using 30 structurally diverse polymers and multidimensional linear regression analysis. “Designer” Tg equations are also derived specifically for acrylate and methacrylate polymers. The work described here demonstrates how molecular modeling can be combined with group additivity theory to yield open‐ended models that are not restricted by lack of requisite group additive parameters and take advantage of three‐dimensional molecular information.
Cation binding properties of photodimerizable polymers bearing benzodiglyme units
Authors: Shirai Masamitsu , Ishida Haruyuki , Tanaka Makoto 
Published: April 2003

AbstractThe polymers which have glyme units as alkali cation binding sites and photodimerizable cinnamoyl units were prepared by the radical polymerization of corresponding monomers. The alkali cation binding ability and selectivity of the polymers, which were studied by a method of picrate salts extraction, were strongly dependent on the length of glyme chains. When irradiated with ultraviolet light, the cinnamoyl groups caused dimerization in dilute solutions. Although the photodimerization of the polymers with relatively short glyme chains enhanced their cation binding ability, the photodimerization of the polymers bearing long glyme chains reduced their cation binding ability. The use of alkali metal cations as templates emphasized the effect of photodimerization on the cation binding properties. The effect of alkali metal cations on the quantum yields of the photodimerization of the polymers showed that two or more benzodiglyme units took part in the binding of one cation. The polymers bearing benzodiglymes, crown ethers, and cinnamoyl moieties were also prepared by the radical copolymerization of the corresponding monomers. It was found that the crown ether units of the copolymers predominantly participated in the cation binding. The photodimerization of the copolymers with suitable alkali metal cations as templates strongly enhanced their cation binding ability.
FT‐IR studies of solvent and temperature effects on poly(diglycidal ether of bisphenol A) (epoxy)
Authors: Janarthanan V. , Thyagarajan G. 
Published: April 2003

AbstractThe infrared spectra of poly(diglycidal ether of bisphenol A) (epoxy) were studied in solutions of chloroform, benzene, and carbon tetrachloride separately to investigate the solvent effect through the behavior of the hydroxyl stretching band. The effect of temperature on the epoxy resin was also studied in this region. The results indicate that there is a varying degree of the weakening of the hydrogen bonding of the hydroxyl group in the epoxy, depending on the solvent. There is evidence also for the formation of hydrogen bonding between chloroform and the hydroxyl group of the epoxy and to a lesser extent between epoxy and benzene.
Angular dependence of 1H‐ and 2H‐NMR spectra of water and methanol absorbed in cellulose triacetate film
Authors: Matsumura Kazunori , Hayamizu Kikuko , Nakane Takashi , Yanagishita Hiroshi , Yamamoto Osamu 
Published: April 2003

Abstract1H‐ and 2H‐NMR spectra of water (H2O and D2O) and methanol (CH3OD and CD3OH) absorbed in cellulose triacetate films have been observed as a function of the angle θ between the film surface and the magnetic field. 1H‐NMR signals of H2O and CH3OD are doublets and triplets due to dipole interactions, respectively. 2H‐NMR signals of D2O, CD3OH, and CH3OD are doublets due to quadrupole splittings. The magnitudes of these splittings change depending on θ. The analysis of the angle‐dependent patterns indicates that the motionally averaged axes of the dipole and the quadrupole moments orient in the direction perpendicular to the film surface. The alignment of water and/or methanol molecules originates from the film morphology, which is anisotropic in the perpendicular direction. From the angle dependence of the chemical shift, the volume diamagnetic susceptibility of the film is estimated to be 0.44 ppm.
Brownian motion of chains and crosslinks in a permanently linked network: The dynamic form factor
Authors: Vilgis T. A. , Boué F. 
Published: April 2003

AbstractWe consider the Brownian motion of crosslinks and chains in a well‐linked network far above the gel point. In a simple mean field approach we model the effect of permanent crosslink constraints by a harmonic potential. The two parameters in this model, the radius of gyration of the mesh and the monomeric friction coefficient, can be determined for most systems. Neglecting entanglements it turns out that the crosslinks and chains are localized within the range of the radius of gyration of a rubber strand between two crosslinks. This is in agreement with the classical phantom model of James and Guth. A crude extension to entanglements shows the restriction of the localization range of the crosslinks. The calculated incoherent scattering can be discussed in the context of experiments recently carried out by Oeser, Ewen, et al., and the coherent scattering is to be compared with current measurements by Oeser, Farago, et al.
Parallel superposition of small‐ and large‐amplitude oscillations upon steady shear flow of polymer fluids
Authors: Isayev A. I. , Wong C. M. 
Published: April 2003

AbstractThe parallel superposition of small‐ and large‐amplitude oscillations upon steady shear flow of elastic fluids has been considered. Theoretical results, obtained by numerical methods, are based upon the Leonov viscoelastic constitutive equation. Steady‐state components, amplitude, and phase angle of oscillatory components of the shear stress, the first and second normal‐stress differences as a function of shear rate, deformation amplitude, and frequency have been calculated. These oscillatory components include the first harmonic of the shear stresses and the first and second harmonic of the normal stresses. In the case of small‐amplitude superposition, the effect of the steady shear flow upon frequency‐dependent storage and loss moduli has been determined and compared with experimental data available in the literature for polymeric solutions and melts. In the case of large‐amplitude superposition, the effect of oscillations upon the steady shear flow characteristics has been determined and compared with our experimental data for a polymeric melt. The experimental results for shear stress components have been found to be in good agreement with theoretical predictions, although there are some deviations for storage modulus at high shear rates. The deviations seem to be dependent on material. Moreover, the theory is unable to describe experimental data available for the first harmonic of normal stresses.
Effect of short‐chain branching on the morphology of LLDPE‐oriented thin films
Authors: Brady Jean M. , Thomas Edwin L. 
Published: April 2003

AbstractHigh‐density polyethylene and randomly branched linear low‐density polyethylene of varying branch length and content were used to produce oriented thin films. Sample morphology was investigated using transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and dynamic mechanical thermal analysis (DMA). Gelation studies suggested that the film preparation technique may have involved gel‐drawing. DSC characterization of samples with approximately equal average branch content revealed very different melting behavior, suggesting differences in crystal size distributions. This was attributed to variations in the distribution of branches within samples. For similar branching distributions, the average melting temperature (and, similarly, crystal size) generally decreased as branch content increased. This was corroborated by TEM, with which crystal thickness was found to decrease as branch content increased. TEM further revealed that the lateral alignment of mosaic blocks and the resultant lamellar character of the thin films was obscured as branch content increased, a result of reduced crystal size, crystallinity, and possibly increased interphase content. DMA of compression‐molded material revealed the presence of a beta peak in branched samples only. Moreover, the alpha transition temperature shifted to lower temperatures as branch content increased.
Surface‐enhanced Raman scattering from bilayers of polystyrene, diglycidyl ether of bisphenol‐A, poly(4‐vinyl pyridine), and poly(4‐styrene sulfonate)
Authors: Venkatachalam R. S. , Boerio F. J. , Roth P. G. , Tsai W. H. 
Published: April 2003

AbstractSurface‐enhanced Raman scattering (SERS) has been observed from thin films of polystyrene (PS), diglycidyl ether of bisphenol‐A (DGEBA), and poly(4‐vinyl pyridine) (PVP) deposited on silver island films Degradation of the polymers occurred rapidly during laser irradiation and was accompanied by the appearance of strong bands near 1375 and 1575 cm‐1. These bands were attributed to the formation of graphite‐like species by the silver‐catalyzed thermal oxidation of the polymers induced by localized laser heating of the substrate. When the thin films of PS, DGEBA, or PVP were overcoated with much thicker films of a second polymer such as polystyrene sulfonate (PSS), the degradation was greatly reduced, and excellent SERS spectra of the PS, DGEBA, and PVP films were obtained. Overlayers reduced degradation within the first films deposited on silver island films by restricting the availability of oxygen at the interface to its solubility in the overlayer polymer or by altering the adsorption of oxygen onto the substrate. SERS was observed for the PS, DGEBA, and PVP films and the PSS overlayers when the films were deposited from relatively dilute solutions. When the PS, DGEBA, and PVP films were deposited from more concentrated solutions, SERS was not observed from the PSS overlayers. It was suggested that most of the SERS was due to a short‐range, charge‐transfer mechanism associated with sites of atomic scale roughness and that SERS was observed from the overlayer when the first film failed to occupy all of the sites.
Crystal growth of polyethylene from dilute solution: Growth kinetics of {110} twins and diffusion‐limited growth of single crystals
Authors: Toda Akihiko , Kiho Hiroshi 
Published: April 2003

AbstractWe have studied the growth kinetics of {110} twins and single crystals of polyethylene in dilute solution of tetrachlorethylene. In terms of {110} twins, we succeeded in obtaining twins without {100} sectors, using a relatively high molecular weight fraction Mw > 104. It is confirmed that the growth is enhanced at the reentrant corner of the twins, and the enhanced growth face inclines to the {110} face because of consecutive generation of steps at the corner. These facts are strong evidence for nucleation‐controlled growth of single crystals. The growth rates and obliquity are measured at various supercoolings and concentrations. From consideration of kinetics of steps on the growth face, the following rates and velocity are independently determined from the experimental data: nucleation rate on a flat face, velocity of step propagation, and generation rate of steps at the reentrant corner. The supercooling dependence strongly supports regime II growth. The results on concentration dependence show that the velocity of steps is proportional to concentration over the whole range examined, and the nucleation rate is independent of it in the usual range and becomes proportional to it in the lower range. This concentration dependence of nucleation rate is attributed to the density of adsorbed polymer on the growth face. From this evidence, it is suggested that the rate of travel of steps is limited by volume diffusion of solute polymer, whereas the growth face is saturated with adsorbed polymer at ordinary concentrations. This contradictory situation could be explained by the hypotheses that the saturation density is rather low and that surface diffusion of adsorbed polymer is much slower than volume diffusion of solute polymer. The lower limit of the rate of folding is also determined for the first time from the velocity of step propagation. As regards the single crystals, it is found that the habit maintains a lozenge shape with sharpened points, even at very high supercooling (δT < 50°C) if the concentration is very dilute. Diffusion‐limited growth is verified for the first time at the higher supercoolings, where the growth rate is almost independent of supercooling. The growth rate becomes almost equivalent to the velocity of steps determined in the experiments with twins, and this fact will support the accuracy of the evaluation of the step velocity. The order of magnitude of the growth rate obtained agrees with the value which is calculated from the balance between the flux of solute polymer to the growth face and the rate of growth of single crystals.
Crystallization studies of poly(ε‐caprolactone). II. Lamellar thickening and melting
Authors: Phillips P. J. , Rensch G. J. 
Published: April 2003

AbstractCrystals of poly(ε‐caprolactone) thicken at a measurable rate at the crystallization temperature. Melting points have been converted into lamellar thicknesses for three molecular weights and the lamellar thickening behavior analyzed using the Sanchez‐Eby approach of a relaxation time for thickening. Isothermal thickening curves are S shaped and can be superposed through horizontal shifts for a given molecular weight. Data for different molecular weights can be superposed using a horizontal shift combined with a small vertical shift. Shift factors have been treated using an Arrhenius approach to give an activation energy for thickening of 100 kcal/mol. Analysis using the Sanchez‐Eby approach leads to the conclusion that the active unit in thickening is approximately one stem length.
Interactions in SMA‐SAN blends
Authors: Kim J. H. , Barlow J. W. , Paul D. R. 
Published: April 2003

AbstractStyrene/maleic anhydride (SMA) and styrene/acrylonitrile (SAN) copolymers have previously been shown to form miscible blends when the MA and AN contents do not differ too greatly. It is shown here that this is the result of a weak exothermic interaction between the MA and AN units by measuring the heats of mixing for appropriate liquid analogs of the various monomer units. The region of copolymer compositions for miscibility of SMA‐SAN blends is predicted from the Sanchez‐Lacombe mixture theory using net interaction parameters calculated from the analog calorimetry results via a simple binary interaction model for copolymers. Lower critical solution temperature behavior was observed for blends of copolymers having compositions near the edge of the miscibility region. Various glass transition, volumetric, and FTIR results are discussed in terms of the interactions observed.