bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of polymerization temperature on the original morphology of polyethylene prepared by γ‐ray‐induced polymerization
Authors: Arai Hidehiko , Wada Takeshi , Kuriyama Isamu 
Published: April 2003

AbstractPolyethylene was prepared by γ‐ray‐induced polymerization in the temperature range 0–180°C. The morphology and the physical properties of the polymer as polymerized were studied by electron microscopy, differential scanning calorimetry, and gel permeation chromatography. Aggregates of small lamellar crystals with irregularly growing faces were produced below 55°C. Aggregates of large spherical particles were formed above 60°C together with hemispherical particles which adhered to the substrate. A few lamellar crystals of triangular or amoeba‐like shapes were also found above 55°C. The polymers formed below 55°C showed a sharp single endothermic DSC peak and a bimodal molecular‐weight distribution, while the sample above 60°C had a double endotherm and a unimodal molecular‐weight distribution. These facts suggest that the mechanism of crystallization during polymerization below 55°C is different from that above 60°C. The melting point, however, decreased continuously with increasing polymerization temperature and was much lower than that of extended‐chain crystals. The results show that the polyethylene, as polymerized, is composed of folded‐chain crystals irrespective of the reaction temperature.
Rheological effects of structure formation in polymer melts
Authors: Andrianova G. P. 
Published: April 2003

AbstractThe viscosity of a number of molten polystyrenes and polypropylenes obtained in various ways from solutions is found to be very strongly dependent on the history of dissolution of the polymer (the concentration of the solution and the “goodness” of the solvent), and on the presence of certain organic oligomeric compounds in very small amounts. The viscosity of the melt may be orders of magnitude less than that of the original samples. The present discussion of these effects is based on the concept of structure formation in amorphous polymers. The structure formed on the solution appears to be very stable with respect to heating and prolonged standing at elevated temperature, although it (and hence the viscosity) strongly depends on the initial concentration of the solution and the nature of the solvent. The role played by additives, present in amounts of small fractions of a percent, is accounted for by the fact that the melt retains the microheterogeneity of the medium. The material moves without its micromosaic structure being disturbed, and the role of the additives is reduced to surface (with respect to structural elements) phenomena.
Study of the low‐frequency motions in poly(ethylene terephthalate) (PET) by neutron inelastic scattering
Authors: Berghmans H. , Groeninckx G. , Hautecler S. 
Published: April 2003

AbstractBy neutron inelastic scattering, a complex low‐frequency spectrum is obtained for PET. This is attributed to the complicated structure of the monomer unit, a large number of intramolecular modes being possible. Most of them were identified using infrared and Raman data. Some indication of the presence of intermolecular modes below 200 cm−1 was found in the dependence of resolution and intensity on temperature in this frequency domain. The existence of these intermolecular modes was further supported by the spectra obtained from oriented or annealed crystalline samples.
Molecular weight distribution and mechanical behavior of PBI fibers
Authors: Wiff D. R. , Gehatia Matatiahu , Wereta Anthony 
Published: April 2003

AbstractTwo different polybenzimidazole (PBI) samples have been investigated in order to correlate the differences in molecular weight distribution (MWD) with changes in the elastic modulus and strength of undrawn and drawn fibers. It has been found that within the weight‐average molecular weight range (7,000 ≤Mw≤ 13,000) there was no obvious correlation withMwandMn. However, one sample had a narrow unimodal molecular weight distribution and the other a wide bimodal molecular weight distribution. The small percentage of high molecular weight present in the latter sample gave its fibers better mechanical properties. X‐ray diffraction studies showed that the orientation in both drawn fiber samples was equal. This isolated the effects of the molecular weight distribution on mechanical properties.
Crystallization during polymerization of diazomethane. II. Studies of model compounds and chain extension of etched polyethylene single crystals by chemical reaction
Authors: Lee Chung Jen , Wunderlich Bernhard 
Published: April 2003

AbstractIn order to study the mechanism of crystallization during polymerization, a method to produce living oligomer crystal nuclei was developed. The living oligomers are diazoketones prepared from their carboxylic acids or acid chlorides. These diazoketones were proved to be reactive toward boron trifluoride etherate. The complex could be further chain‐extended through a living polymerization mechanism with diazomethane. The optimal conditions for the reactions were worked out using model compounds. These reactions were then applied to chain extension of etched polyethylene single crystals. The reactions were confirmed by a combination of time‐dependent differential thermal analysis, molecular weight determination, nuclear magnetic resonance and infrared analysis. The importance and potential application of such reactions for the study of nucleation and crystallization, and final properties of the resulting polymers are discussed.
Incompatibility in polymer solutions: Light scattering of two polymers in a single solvent
Authors: Vrij A. , Van Den Esker M. W. J. 
Published: April 2003

AbstractThe fluctuation theory of light scattering for moderately concentrated polymer solutions is extended in a phenomenological fashion to include angle‐dependent terms up to sin2 (θ/2). The treatment is based on an uncoupling of the center of mass and segment contributions to the free enthalpy. In particular, equations are derived for three‐component mixtures containing two polymer and one solvent component. These are applied near the region of incompatibility. The results are compared with Debye's theory of critical opalescence. It is found that the Debye l parameter should be of the order of magnitude of the radii of gyration of the polymer molecules. This is confirmed by some experiments.
Dielectric relaxation in concentrated solutions of poly(γ‐benzyl‐L‐glutamate)
Authors: Adachi Keiichiro , Hirose Yumiko , Ishida Yoichi 
Published: April 2003

AbstractMeasurements of dielectric constant and loss, broad‐line nuclear magnetic resonance, and differential thermal analysis of concentrated solutions of poly(γ‐benzyl‐L‐glutamate) (PBLG) were carried out to determine the effects of intermolecular interactions on the mobility of the side group and the solvent (dichloromethane or dioxane). Only one dielectric loss peak due to the cooperative motion of the side group and the solvent was found. The activation energy of this relaxation process varied from 3 to 47 kcal/mole with increasing concentration of PBLG from 20 to 100% by weight accompanied with steep increases at about 40 and 80%. This result is explained as due to entanglement of neighboring side groups. In NMR, narrowing of the line was observed near the temperature where the dielectric loss was observed. The glass transition was also observed by differential thermal analysis. From these results it was concluded that the relaxation observed in PBLG solution and in pure PBLG have the nature of primary or α relaxations.
Conformation of poly(dimethyl siloxane) and polystyrene in solution measured by polarized Raman scattering
Authors: Speak R. , Shepherd I. W. 
Published: April 2003

AbstractDepolarization ratios ρ have been measured over ranges of temperature T and molecular weight M for polystyrene (PS) dissolved in cyclohexane (1002 cm−1 Raman band) and for poly(dimethyl siloxane) (PDMS) dissolved in benzene (2907 cm−1 Raman band). The ranges in the case of PS are 15 < T < 65°C and 2 × 103 < M < 4 × 105 and in the case of PDMS are −3 < T < 60°C and M = 104. Measurements were also made of PDMS radii of gyration using conventional light scattering. The results are interpreted in terms of a theory connecting rotational isomeric populations with polymer extension. In the case of PDMS, an experimental value of the proportionality constant for trans isomers (D2 = −3.9 ± 0.9) is deduced. This is closer to the theoretical value than previous estimates but there is still some discrepancy. In the case of PS the isomeric changes resulting from extension are independent of M for M > 104. Deviations are observed for lower M.
Viscoelasticity of dilute chain‐molecule solutions: Evaluation of hydrodynamic interaction
Authors: Wang Francis W. 
Published: April 2003

AbstractThe viscoelastic properties of chain molecules varying in flexibility and length have been calculated by use of the bead‐spring model theory of Zimm. In the evaluation of the hydrodynamic interaction parameter, the number of springs in the bead‐spring model, N, has been selected from the range in which the properties predicted by the theory are insensitive to the value of N. The results for limiting viscosity number agree with those predicted by the Yamakawa–Fujii theory of the limiting viscosity number of wormlike chains. The theory also fits the experimental data of Johnson on a sample of polystyrene of molecular weight 860,000 in theta solvents at infinite dilution. The viscoelastic properties of some moderate molecular weight deoxyribonucleic acid solutions are predicted to deviate from the non‐free‐draining behavior toward the free‐draining behavior.
Nuclear spin relaxation in poly(diethylsiloxane)
Authors: Froix M. F. , Beatty C. L. , Pochan J. M. , Hinman D. D. 
Published: April 2003

AbstractEarlier work showed that heating causes poly(diethylsiloxane) to undergo a first‐order transition from a semicrystalline solid to a more mobile viscous—crystalline material. The latter is composed of two phases and analogies between polymer and liquid crystal morphology and behavior have been made. The viscous—crystalline phase in PDES appears to be unique since the literature is devoid of other documented examples. In this study, spin—lattice and spin—spin relaxation times were measured over a wide temperature range. They show a glass transition at 138°K, a crystal—crystal transition at 206°K, and a transition around 250°K which results from translational motion of the polymer chains with respect to each other. This motion is observed in the amorphous phase at a lower temperature than in the crystalline phase. Translational motion in the crystalline phase is observed on melting of the crystallites. The spin—spin data permitted monitoring of the molecular motions in each phase and the data suggest that these phases exert some influence on the molecular motions of each other. The viscous—crystalline phase in PDES may represent a unique model for studying and understanding “precrystalline” behavior and structure in amorphous solids.
Dielectric relaxation studies in poly(hexamethylenesebacate) (HMS), poly(2‐methyl‐2‐ethyl propylenesebacate) (MEPS), poly(2,5‐dimethylbutylene sebacate) (DBS), and block copolymers of HMS and MEPS
Authors: Pochan John M. , Hinman Darlyn F. 
Published: April 2003

AbstractThe α and β dielectric relaxations of poly(hexamethylenesebacate) (HMS), poly(2‐methyl‐2‐ethyl propylenesebacate) (MEPS), poly(1,4‐ dimethylbutylene sebacate) (DBS) and block copolymers of HMS and MEPS have been studied. The α relaxation is amenable to a W.L.F. analysis and is associated with the glass transition of the polymers. This relaxation moves to higher temperatures with increasing HMS content in HMS/MEPS block copolymers. All the polymers studied exhibit psuedo‐activation energies of ∼32 kcal/mole at the glass transition. It is concluded that because the superposition principle is operative in the block copolymers, the glass transition must be very similar in both polymers and morphology and degree of crystallinity do not greatly affect this transition. The β relaxation which has been associated with segmental relaxation of polymethylene segments in polymers is also shown to be a function of HMS/MEPS block copolymer composition and chemical structure. This relaxation takes place at lower temperatures with increased HMS content in the blocks and also shifts to lower temperatures with side chain substitution adjacent to the carbonyl group in the polymer. It is concluded that the β relaxation takes place in the amorphous and crystalline regions of the polymer.
Electro‐osmosis of water through a cellulose acetate membrane
Authors: Srivastava R. C. , Jain Abhay K. 
Published: April 2003

AbstractExperiments on electro‐osmosis of water through a cellulose acetate membrane have been reported and the data analyzed in the light of nonequilibrium thermodynamics. The linear phenomenological equations have been found to be valid. Study of the directional dependence of phenomenological coefficients has revealed the anisotropic character of the membrane. Efficiency of energy conversion for both electro‐osmosis and streaming potential has been calculated and the results have been analyzed in the light of thermodynamic theories.
The elongation and time dependence of the crystallinity of low‐density polyethylene
Authors: Peiffer D. , Hong S. D. , Stein R. S. 
Published: April 2003

AbstractIt has been presumed in studies of the orientation of low‐density polyethylene and its time dependence that the degree of crystallinity remained constant with elongation and did not vary with time following elongation. This paper represents a test of this hypothesis by several methods. The change in crystallinity accompanying stretching has been followed by a modification of an x‐ray method for uniaxial orientation proposed by Ruland in which diffraction peaks are resolved into crystalline and amorphous components and their respective areas are determined by two‐dimensional integration over both the Bragg angle and the azimuthal angle of diffraction. The weight‐fraction crystallinity is then determined from the ratio of the weighted crystalline area to the total area. There appears to be no significant variation in crystallinity up to 50% sample elongation for both slowly and rapidly stretched samples at room temperature. The dynamic crystallinity change accompanying small amplitude vibration has also been determined by the dynamic x‐ray diffraction technique and found to be negligible over a wide range of frequency. The degree of crystallinity has also been evaluated from the absolute infrared absorbance of crystallinity‐sensitive bands and has also been found to be independent of elongation at room temperature up to 80% elongation. Changes have also been observed by this method during relaxation at constant length following rapid extension and have also been found to be negligible. These results also indicate negligible changes in rotational isomer population. Consequently, we conclude that changes observed during relaxation and vibration arise from orientational changes rather than changes in the degree of crystallinity.
Dipole moments in oriented poly(ethylene terephthalate)
Authors: Hsu Bay‐Sung , Kwan Sik‐Hung , Wong Lai‐Wah 
Published: April 2003

AbstractDielectric experiments were performed in the β temperature region on poly(ethylene terephthalate) films of different draw ratios. The proportion of various conformations, crystallinity, and orientation were estimated from infrared, density, and birefringence measurements. The dielectric relaxation strength was determined from the Cole–Cole plot of the dielectric constants over a wide frequency range. An attempt was made to modify the Fröhlich equation, originally for isotropic systems, for application to systems of oriented dipoles. When the experimental data are analyzed through this modified equation, it is evident that the changes in the dielectric constants of PET with stretching could not be accounted for by improvement in the alignment of chain molecules alone. The relative abundance of the trans conformation, both crystalline and amorphous, and gauche conformation appears to be a factor which cannot be ignored. The calculation indicates that the dipole moment seems to be greater in the trans conformation than in the gauche conformation.
Heterogeneous nucleation of crystallization of high polymers from the melt. II. Aspects of transcrystallinity and nucleation density
Authors: Chatterjee A. M. , Price F. P. , Newman S. 
Published: April 2003

AbstractIn the initial stage of the development of transcrystallinity, nuclei appear sporadically on the substrate. The growth rate and melting temperature of the transcrystalline region are found to be the same as those of spherulites nucleated in the bulk of the polymer. Nucleation densities ns at the interface, and nb in bulk, for the crystallization of isotactic polypropylene, poly(ethylene oxide), and poly(butene‐1) in contact with various substrates, have been measured by counting the number of spherulites generated. Despite variations in the results from various causes, the quantities ns and ns/nb are useful parameters for characterizing the nucleating ability of various substrates.
Bromination of single crystals of trans‐1,4‐polybutadiene. Thermal behavior
Authors: Marchetti Antonio , Martuscelli Ezio 
Published: April 2003

AbstractIt is demonstrated by several methods (DSC, infrared spectroscopy, and small‐angle and wideangle x‐ray diffraction) that bromination of suspensions of single crystals of trans‐1,4‐polybutadiene is selective at the fold surface. As the thickness of the single crystals is increased, a larger number of double bonds per fold are brominated, i.e. a larger number of repeat units become accessible to bromine. This is consistent with an increase in the thickness of disordered surface layers with the crystallization temperature. A reduction of 40–60% in overall apparent enthalpies of transition and of melting and reduced ability of brominated single crystals to refold following annealing are also observed. Crystallization from the melt of trans‐1,4‐PBD with [ CH2CHBrCHBrCH2 ] units along the chain is interpreted by assuming that some of these units are incorporated in the crystal lattice as defects.
Abnormal viscosimetric behavior of homopolymers in mixed solvents and preferential solvation
Authors: Dondos A. , Benoit H. 
Published: April 2003

AbstractIt is shown that the applicability of the Stockmayer–Fixman–Burchard plot is much more limited in the case of solvent–precipitant mixtures than in the case of pure solvents. The observed deviations can be explained by taking into account the variation of preferential solvation as a function of the molecular weight of the polymer. More precisely the average density of the segments in the region occupied by the coiled molecule seems to be the parameter governing both changes in viscosity and in preferential solvation.
The existence of mosaic block structures in polymer single crystals
Authors: Harrison Ian R. , Runt James 
Published: April 2003

AbstractX‐ray line broadening measurements were used to determine the apparent “mosaic block” sizes of randomly oriented polyethylene and polyoxymethylene single crystals. Both dried‐down and uncollapsed crystals were examined. PE lamellae were grown at 80, 85, and 90°C by isothermal crystallization from a 0.1% solution in xylene. POM crystals were grown at 125°C by self seeding from an 0.05% solution of the polymer in o‐dichlorobenzene. A given preparation was split into two parts. One part was dried down in the usual manner, the other was exchanged to paraffin oil and the crystals never permitted to dry down. Previously reported studies used dried‐down crystals and gave crystallite sizes of approximately 300 Å. More recently, using electron microscopy, it has been postulated that PE single crystals are free of “mosaic block” over regions of several thousand angstroms. It is evident from this present study that crystallite sizes in uncollapsed lamellae are significantly larger than those observed for the same crystals dried down. In the case of uncollapsed lamellae, one can explain the observed crystallite sizes solely on the basis of chain obliquity rather than by invoking the “mosaic block” model. It has also been determined that there is an upper limit to the crystallite sizes that can be observed in PE and POM crystals using wide‐angle x‐ray techniques. This limit may account for discrepancies between x‐ray and electron diffraction.
Nuclear magnetic resonance studies on microstructure of ethylene copolymers. VII. Proton resonance spectra of hydrolyzed ethylene–vinyl acetate copolymers1
Authors: Wu Ting Kai 
Published: April 2003

AbstractComplete and partial alcoholyses of ethylene–vinyl acetate (E–VA) copolymers yield ethylene–vinyl alcohol (E–VOH) copolymers and ethylene–vinyl acetate–vinyl alcohol (E–VA–VOH) terpolymers, respectively. From the 220‐MHz proton NMR spectra of E–VOH copolymers the stereoregular and chemical sequence distributions of the comonomers can be readily determined. Partially hydrolyzed E–VA polymers were acetylated with perdeuterated acetic anhydride. The monomer distributions in the terpolymers were then quantitatively determined by examining the proton spectra of the derived products. It was found that alcoholysis of E–VA polymers occurs preferentially at VA units which have neighboring VA groups.
On the structure of glassy polymers. IV. Small‐angle x‐ray scattering from rigid polyvinyl chloride
Authors: Straff R. S. , Uhlmann D. R. 
Published: April 2003

AbstractThe small‐angle x‐ray scattering (SAXS) from quenched and annealed rigid polyvinyl chloride (PVC) has been measured using a Bonse–Hart system. After correcting for absorption, background, and beam divergence, the scattering has been placed on an absolute basis using a standard silica suspension as a reference. The scattering from annealed (6 days at 75°C) and unannealed PVC was identical within experimental error, varying with scattering angle in a manner similar to the SAXS from other amorphous polymers. The intensity decreases rapidly with increasing scattering angle over the ranges from 20 sec to 20 min. Beyond 20 min the intensity is fairly constant, decreasing only slightly with increasing angle. At the largest angles of measurement (in the range of 120 min), the measured intensity is close to the value calculated for thermal density fluctuations frozen‐in at the glass transition.The angular variation of intensity is well described by the scattering from heterogeneities of various sizes and concentrations superimposed on the scattering from thermal density fluctuations. These heterogeneities range in radius from 50 to 4500 Å and, assuming the crystalline excess density, the total concentration of heterogeneities is less than 0.5%. The mean‐square fluctuation in density, determined from the measured intensity invariant, is also consistent with such a distribution of heterogeneities.The present SAXS results on rigid PVC are inconsistent with the presence of nodular features as representative of the bulk polymer. Rather, it is suggested that they are associated with surface effects. It is further suggested that previously indicated volume fractions of crystallinity in rigid PVC (generally in the range of 5–12%) are incorrect, and that the model of a three‐dimensional network of crystallites used to explain the rheological behavior of this material should be re‐examined.
Direct observation of polyethylene molecules with electron microscopy
Authors: Furuta Motonobu 
Published: April 2003

AbstractIndividual polyethylene molecules have been imaged in the electron microscope. Preparative difficulties are overcome by the following procedures. (1) The polymer is dissolved in n‐hexadecane at 130°C; (2) the solution is deposited on a cooled substrate by spraying in an atmosphere of cold nitrogen; (3) the deposited polymer molecules were shadowed by platinum. Molecular weights obtained are in good agreement with those from light scattering.