bluuebunny/crossref_metadata_2025_split huggingface dataset:
The microstructure of poly(vinyl chloride) as revealed by x‐ray and light scattering
Authors: Wenig W. 
Published: April 2003

AbstractSmall‐angle x‐ray scattering (SAXS) and wide‐angle x‐ray scattering (WAXS) as well as small‐angle light‐scattering (SALS) techniques have been applied to investigate the microstructure of a number of commercial poly(vinyl chloride) (PVC) samples. From the wide‐angle x‐ray scattering, crystallinity and crystal size parameters have been determined. The crystallinity of the samples investigated range from 5% to 10%. Superstructure parameters such as crystallite thickness, distribution functions of crystallite and amorphous thicknesses, and size of ordered regions have been obtained by an analysis of the SAXS curves using the cluster model. The crystallinity agrees well with the WAXS crystallinities indicating that most of the crystals are lamellar shaped, though some rodlike entities are present in the sample as is shown by the small‐angle light scattering. From the SAXS analysis, the microstructure is described as clusters of lamella stacks which are identical with the subprimary particles. Their size is determined to be 220–240 Å. Emulsion type PVC also contains lamellar‐shaped crystals. The superstructure, however, of this type of PVC is different from that of mass or suspension‐polymerized material. The SAXS curve does not reveal any correlation between the crystals.
Simultaneous nonlinear diffusion of a solvent and organic penetrant in a polymer
Authors: Frisch H. L. 
Published: April 2003

AbstractWe obtain the exact solution of a fairly large class of somewhat simplified problems involving the simultaneous nonlinear Fickian diffusion of a poor solvent and a dilute organic penetrant, such as a plasticizer, in a semi‐infinite polymer slab immersed in the solvent bath. Such problems can also provide useful estimates during certain time regimes of release of drugs from implants, and pesticides and pheromones from certain slow or controlled‐release polymeric devices, insofar as these are affected by an environmental solvent bath. We assess the effect of various simplifications made (e.g., neglect of the penetrant concentration dependence in the diffusion coefficient, cross diffusion of solvent and penetrant, and a variety of boundary conditions) by solving exactly some additional specialized cases.
Interpretation of spin relaxation in polyisobutylene in terms of specific motions
Authors: Jones Alan Anthony , Lubianez Ronald P. , Hanson Mark A. , Shostak Shelley L. 
Published: April 2003

AbstractPorton and carbon spin‐lattice relaxation times T1 and nuclear Overhauser enhancements are interpreted in terms of motions likely in linear polyisobutylene. Most of the interpretation is based on relaxation data in the literature, but some additional 1H and 13C pulse Fourier transform experiments were conducted to resolve a disagreement in the literature concerning cross relaxation between the two types of protons present in polyisobutylene. Spin relaxation in solution and the bulk is accounted for by three specific motions considered as independent sources of motional modulation of the dipole–dipole interaction. The first motion is overall isotropic rotatory diffusion which has a known dependence on molecular weight, intrinsic viscosity, and solvent viscosity for polymers in solution, and a known dependence on molecular weight and viscosity for bulk polymers. The effects of overall tumbling account for a decrease of T1 for the methylene and methyl carbons with increasing molecular weight in solution and increase of T1 of methylene carbons with molecular weight in bulk. The second motion considered is backbone rearrangements caused by the three‐bond jump. This motion dominates relaxation of the methylene carbons either in solution or in the bulk allowing for the determination of the associated correlation time. The correlation time characterizing the occurrence of the three‐bond jump in a 5% (wt/vol) solution in CCI4 at 45°C is 58 psec, and in the bulk at 45°C it is 11 nsec. The last motion included in the model is methyl‐group rotation about the threefold symmetry axis. The methyl‐group rotational correlation time is 0.20 nsec in a 5% (wt/vol) solution in CCI4 at 45°C and 0.33 nsec in the bulk at 45°C. The concentration dependence of the backbone motion contrasts strongly with the corresponding dependence of methyl‐group rotation.
Dielectric study of side‐group rotation of methyl methacrylate in copolymers
Authors: Mashimo Satoru , Yagihara Shin , Iwasa Yasuo 
Published: April 2003

AbstractThe dielectric absorption due to the side‐group rotation of the methyl methacrylate (MMA) unit in MMA‐styrene and MMA‐p‐chlorostyrene (pCS) copolymers was measured. The relaxation time for MMA‐pCS copolymers with low MMA contents could be interpreted quantitatively in terms of the Kramers rate‐constant theory at the low‐friction limit. On the other hand, the frictional effect on the relaxation time could not be ignored for any copolymers except for the MMA‐pCS copolymers with low MMA contents. The relaxation time for pure poly(methyl methacrylate) could be interpreted by the Kramers theory at the high‐friction limit.
High‐speed aqueous gel‐permeation chromatography
Authors: Hashimoto Tsutomu , Sasaki Hiroo , Aiura Makoto , Kato Yoshio 
Published: April 2003

AbstractHigh‐speed gel‐permeation chromatography (GPC) of water‐soluble polymers has been investigated by using TSK‐GEL, type‐PW columns packed with small porous particles. Being semirigid, the column packing could be operated under high pressure and, therefore, it was possible to achieve high‐speed GPC. A resolution higher than that of ordinary GPC in organic solvent system was attained when the measurement of one sample was completed within 40 min with a 6‐ft column set. Samples with a wide range of molecular weights, from oligomers to polymers having a molecular weight greater than 106, could be fractionated. Dextran, polyethylene glycol, polyacrylamide, poly(vinyl alcohol), and poly(vinyl pyrrolidone) were separated according to molecular size with no evidence of adsorption. Investigation of other water soluble polymers is now in progress.
Kinetics of epoxidation of poly(trans‐1,4‐butadiene) crystals in suspension
Authors: Wichacheewa P. , Woodward A. E. 
Published: April 2003

AbstractThe kinetics of the epoxidation reaction between metachloroperbenzoic acid (MCPBA) and poly‐(trans‐1,4‐butadiene), (PTBD), crystals in toluene suspension was investigated in the 6–21°C range using infrared spectroscopy. Crystals of PTBD with M̄n = 36,000 grown from heptane and from toluene solutions and crystals of PTBD with M̄n = 5500 grown from heptane were studied. For toluene‐grown crystals the total number of double bonds available for reaction increases with reaction temperature. For all preparations studied the epoxidation reaction is initially second‐order—first‐order with respect to [MCPBA] and first‐order with respect to the concentration of the available double bonds. The second‐order rate constant is found to be dependent on temperature, on molecular weight, and also on the crystal preparation conditions. The bromination of PTBD crystals was studied in CCl4 suspension at 0°C; this reaction was found to be complete within 1 hr with the fraction of double bonds brominated consistent with the epoxidation results. The IR spectra for dried mats of brominated and of epoxidized PTBD crystals were obtained: Changes in the amorphous band at 1335 cm−1 due to reaction of double bonds at crystal surfaces were observed. The results of this investigation are discussed in terms of the amorphous content of the PTBD lamellas.
Epitaxial crystallization of polyoxymethylene during cationic polymerization of trioxane
Authors: Takahashi Toshisada , Okazaki Hideo 
Published: April 2003

AbstractEpitaxial crystallization of polyoxymethylene (POM) during cationic polymerization of trioxane in ethane dichloride was studied. Nascent POM crystals grew epitaxially on the surface of drawn, high‐molecular‐weight POM and on the (001) surface of KCl single crystals. Half‐hexagonal crystals several thousand angstroms in thickness were formed on these substrates. No discrete diffraction maximum could be observed in small‐angle x‐ray scattering patterns, but diffuse streaks were present on both the equator and the meridian of the pattern. These diffuse streaks are due to inhomogeneities in the nascent crystals. It is proposed that the crystals contain voids due to occlusion of reactive chain ends in the crystal. The optical diffraction pattern from a model made up of rectangles agreed qualitatively with the actual x‐ray pattern.
Longitudinal acoustic mode in polymers. IV. LAM‐3 of the general perturbed rod and applications to paraffins and polymers
Authors: Krimm S. , Hsu S. L. 
Published: April 2003

AbstractThe dependence of the LAM‐3 frequency on the various parameters of a perturbed composite elastic rod has been calculated. Together with the previously calculated nonlinear variation of LAM‐1 with these parameters, it can be expected that experimental measurements of both of these bands will permit a more detailed analysis of properties of long‐chain molecules. The predictions of the theory are in complete agreement with experimental results on n‐paraffins. For data on polyethylene and poly(ethylene oxide) reasonable solutions can be found, although the experimental information on polymers is not yet accurate enough or sufficiently devoid of assumptions to permit definitive conclusions to be reached.
Molecular orientation in poly(vinyl chloride) studied by Raman spectroscopy and birefringence measurements
Authors: Robinson M. E. R. , Bower D. I. , Maddams W. F. 
Published: April 2003

AbstractThe ratios of the intensities of Raman scattering in the CCI stretching region for eight combinations of sample orientation and directions of polarization of incident and scattered light have been measured for 15 samples of poly(vinyl chloride) (PVC) containing 0, 5, 10, 15 or 20 pph dioctyl sebacate (DOS) plasticizer which had been drawn uniaxially at 22, 70, 75, 80, or 90°C to draw ratios in the range 1–4.5. The birefringences of the samples were also measured. The Raman data were analyzed to give 〈P2(cosθ)〉cryst and 〈P4(cosθ)〉cryst, the values of the second‐ and fourth‐order Legendre polynomials in cosθ averaged over the distribution of orientations of the crystallites, where θ is the angle between the c axis of a typical crystallite and the draw direction. Comparison of 〈P2(cosθ)〉cryst with the birefrigence showed that the crystallites are more highly oriented than the noncrystalline material in samples containing the higher amounts of plasticizer drawn at the higher temperatures. A value of 13.0 × 10−3 was deduced for the birefringence of fully oriented PVC. The values of 〈P4(cosθ)〉cryst for a given 〈P2(cosθ)〉cryst were found to be higher than predicted by calculations based on two simple models, the pseudoaffine rigid‐rod rotation model and the affine rubber elasticity model.
Ultrahigh draw ratios in polyethylene: Molecular weight effects
Authors: Warner S. B. 
Published: April 2003

AbstractRemoval of the ultrahigh molecular weight fraction in high‐density polyethylene by hydrodynamic crystallization and analysis of the subsequent drawing behavior leads to the conclusion that the small portion of extremely long chains present in polymers with a log‐normal molecular weight distribution is not necessary for the achievement of high draw ratios, that is, in excess of 30×. Furthermore, a certain minimum weight, and therefore chain length, is required for the attainment of high draw ratios. For example, paraffins with a molecular weight of 23,000 draw only up to about 5×. A logical extension of these concepts to other polymer systems is presented.
Transient and steady‐state permeation in poly(ethylene terephthlate) above and below the glass transition
Authors: Koros W. J. , Paul D. R. 
Published: April 2003

AbstractTransient and steady‐state permeation data are reported for CO2 in semicrystalline poly(ethylene terephthalate) for temperatures ranging from 25 to 115°C over the pressure range from 1 to 20 atm. The pressure dependency of the time lag and permeability disappears completely above the glass transition of the polymer, and Fick's law with a concentration‐independent diffusion coefficient applies. In the glassy state, a concentration‐dependent diffusion coefficient is necessary to describe the data. The form of this concentration dependence is described well by the partial immobilization transport model that attributes a different mobility to each of the two populations of sorbed gas which exist in local equilibrium with each other in glassy polymers. The importance of reporting the pressure used in transport experiments involving glassy polymers is emphasized by comparing the difference in the activation energy of the apparent diffusivity calculated from the measured time lag at 1 and 20 atm. Also, the magnitude of the observed slope discontinuity at Tg in Arrhenius plots of these apparent diffusities is shown to be a function of the upstream pressure used in the experiment. The independently measured time lags are compared with the predicated values calculated from various transport models and found to be described best by the partial immobilization model.
Vibrational spectra and normal coordinate analysis of isotactic poly(alkyl ethylene)s II. Modification I of poly(propyl ethylene) and its deuterated derivatives
Authors: Holland‐Moritz K. , Sausen E. , Djudovic P. , Coleman M. M. , Painter P. C. 
Published: April 2003

AbstractThe vibrational analysis of modification I of poly(propyl ethylene), poly(propyl ethylene)‐(2,2;d2), and poly(propyl ethylene)‐(1,2,2;d3) has been performed using the valence force field derived for poly(ethyl ethylene) and the actual molecular geometry. The band assignments are based on infrared polarization and Raman data.
Heat capacity of poly(vinylidene fluoride) and polytetrafluoroethylene between 5 and 200°K
Authors: Choy C. L. , Leung W. Y. , Chen F. C. 
Published: April 2003

AbstractHeat capacities of poly(vinylidene fluoride) (PVF2) and polytetrafluoroethylene (PTFE) have been measured between 5 and 100°K with an accuracy of (1–5)% by adiabatic calorimetry. Calculations based on contributions from known optical lines and the Tarasov continuum model are in good agreement with experimental results down to 30°K for PVF2 and 10°K for PTFE, and yield characteristic temperatures θ1 and θ3 which are consistent with previous values determined from high‐temperature (100—350°K) data. At lower temperature the measured heat capacity is significantly higher [(30–100)%] than the model prediction, and can be satisfactorily accounted for by the introduction of localized vibrators at a concentration of about 1% as compared to acoustical oscillators and at a characteristic temperature of about 20°K. Using established data on polyethylene for comparison, the principle of additivity for heat capacities is found to be valid down to at least 20°K, convering the region (<60°K) where interchain vibrations contribute significantly to the heat capacity. Possible reasons for this unexpected behavior are discussed.
Vapor‐induced depolarization currents in electrets
Authors: Cantaloube B. , Dreyfus G. , Lewiner J. 
Published: April 2003

AbstractThe charge decay of polymer electrets in the presence of solvent vapor is analyzed. In order to account for this phenomenon, several hypotheses are considered and tested experimentally. It is shown that the penetration of the solvent is responsible for the observed charge decay, and that it is the rate limiting factor. Moreover, the phenomenon is not due to the screening of the injected charges, but to the motion of these charges, which are liberated by the penetration of the solvent. Finally, the possible applications of this phenomenon in investigations on both the microscopic and macroscopic scale are outlined.
Least‐squares refinement of molecular structure of polyoxymethylene
Authors: Takahashi Yasuhiro , Tadokoro Hiroyuki 
Published: April 2003

AbstractLeast‐squares refinement of the molecular structure of polyoxymethylene was carried out by using intensity data measured with an automatic four‐circle diffractometer. The discrepancy factor was improved to 4.1% by using the anisotropic temperature factor. Physically significant values were obtained for the bond length, bond angles, and internal rotation angle: CO = 1.429 ± 0.008 Å, ∠COC = 112.9 ± 0.6°, ∠OCO = 110.4 ± 0.8°, and τ(CO) = 77.0 ± 0.3°. Samples for x‐ray diffraction measurements were prepared by solid state polymerization of a tetroxocane single crystal.
Simulation of the brownian motion of macromolecular chains. II. Chain dynamics
Authors: Gény F. , Monnerie L. 
Published: April 2003

AbstractA simulation of the Brownian motion of polyethers and polyethylene is reported. The chains under consideration are confined to a tetrahedral lattice and subjected to conformational energy conditions. The dynamic behavior of the whole chain is studied. The diffusion of individual chain atoms reflects the chemical nature of the chain, and the diffusion of the center of mass, in connection with experimental results, affords a time scale for the simulation. The relaxation of bond orientation, which is connected with fluorescence depolarization, is found to be consistent with the theory of Valeur and co‐workers. The relaxation of the total dipole is interpreted in terms of conformational features of the motions and correlations between neighboring dipoles. Finally, relations between chemical structure and dynamic behavior are established. Three classes of polyether chains are to be distinguished: the rigid chain poly(methylene oxide), the highly flexible poly(ethylene oxide) and an intermediate class typified by polyethylene.
Evidence of distinct water species in cellulosic environments from broad‐line NMR
Authors: Fleming William W. , Fornes R. E. , Memory J. D. 
Published: April 2003

AbstractBroad‐line NMR measurements were made on water in cellulosic samples. The spectra for oriented rayon at 65% relative humidity and room temperature consisted of a visually apparent doublet (SD) and a narrow singlet (SN) which was shifted upfield about 7 ppm from the center of the doublet. The doublet separation varied as A(3 cos2θ—1), where θ is the angle between the fiber axis and the magnetic field; the maximum doublet separation was 350 mG at both 15.1 and 56.4 MHz, indicating the doublet is dipolar in origin. The peak‐to‐peak linewidth of the narrow singlet was orientation and field dependent. The upfield shift of the narrow singlet from the doublet center was field dependent. Spectra for vacuum‐treated rayon consisted of only the narrow singlet, which was orientation dependent. The doublet separation decreases with increasing moisture content and is essentially zero for oriented rayon samples at 100% relative humidity; the resulting spectra due to the collapsed doublet and SN singlet was an asymmetric line. Temperature‐dependent measurements were made on oriented rayon at 65% relative humidity with the fiber axis parallel to the magnetic field; when the temperature was increased from about 0° the peak‐to‐peak linewidth of the doublet halves and the doublet separation decreased. As the temperature was increased from about 30 to about 65°C, a previously unobserved singlet (SE) became visible. The relative amplitudes of the three lines varied with temperature as follows: The SE singlet increased, the SD doublet decreased, and the amplitude of the SN singlet remained constant. Measurements using oriented cotton samples and randomly packed rayon samples indicated that the NMR line shape of the water spectra depends upon the physical properties of the macromolecular substrate. The doublet component of the spectra is attributed to a water species (SD) which is highly bonded to the macromolecular substrate. The SE singlet is attributed to an energetic water species (SE) which is rapidly tumbling in the macromolecular environment. The SN singlet is not due to free water.
Stress‐induced crystallization of poly(ethylene terephthalate)
Authors: Misra A. , Stein R. S. 
Published: April 2003

AbstractQuenched amorphous films of poly(ethylene terephthalate) (PET) are stretched at temperatures less thanTg; changes in density, wide‐angle x‐ray diffraction, and small‐angle light scattering are observed. The density increase upon stretching is attributed to an increase in crystallinity accompanied by an increase in the intensity of somewhat diffuse wide‐angle x‐ray diffraction and of bothVVandHVsmall‐angle light scattering patterns. The formation of oriented rodlike superstructure may be discerned from small‐angle light scattering. Annealing of these samples increases the crystallinity as measured from density and leads to an increase in the perfection of crystalline and supercrystalline structure as measured by wide‐angle x‐ray diffraction and small‐angle light scattering. The rodlike morphology changes to form spherulitelike aggregates as observed by small‐angle light scattering and light micrographs. A model is proposed to explain the observations. Studies are extended to stretching films of PET above theirTgand observing changes in birefringence, density, wide‐angle x‐ray diffraction and small‐angle light scattering as a function of elongation and stretching temperature. The formation of defomed spherulitelike superstructure may be discèrned from light micrographs. Results are compared with those obtained upon stretching films belowTg.
Reactivity and gelation. I. Intrinsic reactivity
Authors: Durand Dominique , Bruneau Claude‐Marcel 
Published: April 2003

AbstractThe method of Case is used with the Flory‐Stockmayer gelation criterion to derive a critical transition equation for polycondensation of multifunctional reactants bearing coreactive functional groups of two species A and B, where the B groups may be of unequal intrinsic reactivity. Systems of the types R(A)2/R′(B)4 and R(A)2/R′(B)4/R′′(B)2 are considered with the B groups divided into two classes characterized by a reactivity ratio in the range 0.1 to 10. If the reactivities are sufficiently different the polymerization can be regarded as a multistage process. Intramolecular reactions are not considered.
Reactivity and gelation. II. Substitution effect
Authors: Durand Dominique , Bruneau Claude‐M. 
Published: April 2003

AbstractThe development in Paper I is extended to multifunctional condensations where the functional groups exhibit unequal reactivities induced by substitution effects in the course of the polymerization. A system R(A)2/R′(B)3 is examined to determine how the gel point varies with the strength and positive or negative sense of the substitution effect. As in Paper I, intramolecular interactions are not considered.
Orientation of the remaining amorphous chains during crystallization: Isotactic polystyrene
Authors: Krigbaum W. R. , Taga Tooru 
Published: April 2003

AbstractThe orientation of statistical chain segments in the amorphous regions of a semicrystalline polymer can be characterized quantitatively by x‐ray diffraction. A calculated background (which is orientation independent) must be subtracted, which requires that the intensity profile of the amorphous halo be measured on an absolute scale. Application is illustrated to samples of isotactic polystyrene which were isothermally crystallized at fixed elongation. These samples differ from those of the previous study due to the unintentional introduction of a small amount of crystallinity (0.25% to 1%) which serves as tie points in the drawing operation, giving a stronger amorphous orientation. Preferred orientation of the amorphous chain segments is rapidly depleted during the first few percent of crystallization. The crystallite orientation distribution is quite sharp, and broadens only slowly with crystallization. These results imply that, for the crystallization conditions employed, the crystallite orientation must be determined by nuclei which are formed at the earliest stages of the crystallization process.