bluuebunny/crossref_metadata_2025_split huggingface dataset:
Irradiation of crystalline polyethylene
Authors: Salovey Ronald 
Published: April 2003

AbstractMeasurements of crosslinking, unsaturation, and hydrogen evolution following electron bombardment are similar for bulk polyethylene and fast‐filtered single crystals. Slow‐filtered single crystals evidence a unique irradiation behavior. It is suggested that irradiation‐induced crosslinking is preferentially between the layers of polyethylene single crystals if the lamellae are in close contact. Following slow filtration the lamellae are separated while fast filtration of single crystal preparations brings the lamellae into contact. Moreover, it is possible that the bulk polymer is composed of folded molecules in compacted lamellae.
Synthesis of graft copolymers by a transesterification method
Authors: Kolesnikov H. S. , Khan'‐Min Tsen 
Published: April 2003

AbstractIt is shown for the first time that mutual transesterification between carbochain polyesters (polymethyl methacrylate) and heterochain polyesters may be used for synthesizing graft copolymers. The graft copolymers obtained from polymethyl methacrylate and crystalline polyesters are crystalline have high softening temperatures. The grafting of amorphous polyesters yields amorphous graft copolymers. An increase in the number of graft side chains is accompanied by a decrease in intrinsic viscosity of the copolymer and by a rise in value of the Huggins constant. The decrease in the intrinsic viscosity is not the result of a degradation process, since polymethyl methacrylate may be regenerated by methanolysis of the graft copolymers. The intrinsic viscosity of the regenerated polymethyl methacrylate is equal to that of the initial polymer. Graft copolymers from polymethyl methacrylate and heterochain polyesters possess a lower tensile strength and higher ultimate elongation than polymethyl methacrylate. It was also established that on heating mixtures of methyl methacrylate and ω‐hydroxyacids in the presence of a catalyst graft copolymers form by simultaneous polymerization, polycondensation, and mutual transesterification reactions. Some correlations in this process and the properties of the resultant graft copolymers have been studied.
Interfacial polycondensation. XII. Variables affecting stirred polycondensation reactions
Authors: Morgan Paul W. , Kwolek Stephanie L. 
Published: April 2003

AbstractPreceding papers have described the preparation of many polymers in high molecular weight by interfacial polycondensation under a wide variety of conditions. This paper reports an extended study of the optimum conditions for the stirred preparation of poly (hexamethylene sebacamide) and poly(sebacyl piperazine). The first is a polymer which precipitates from the reaction mixture while the latter may be retained in solution in the organic solvent. For each polymer‐solvent system there are selected conditions which produce a maximum in the viscosity number of the product. The peaks arise from varying the reactant concentrations and the ratio of the water to organic solvent. Their position is influenced by such factors as the polymer‐solvent interaction, the quality of the stirring, the presence of detergents, and the solubility characteristics of the diamine. The optimum conditions results from a balance of these various factors. Maximum molecular weight is achieved when equivalents of the two reactants are brought together in a narrow reaction zone near the interface and within the limited time in which the growing polymer is mobile. The high points in molecular weight often coincide with the highest yield of polymer. For 6‐10 polyamide it was shown further that the number of acid and amine chain ends per unit weight of polymer are nearly equivalent and at a minimum. At the same time the moleculare weight‐viscosity relation deviates least from that derived for polyamide made by melt polycondensation. Reaction rates are preferable high but successful polycondensations will result with slower reactions as long as there are no strongly competing side reactions and the growing polymer is kept mobile. The hydrolysis rates of short chain aliphatic diacid chlorides was found to be very high and yet this did not prevent the preparation of polyamides with hexamethylenediamine with ηinh above 0.5. Monofunctional impurities in the intermediates and solvents may limit molecular weight. Such materials were purposely tested with polyamides, polyesters, and polyurethanes. Their effectiveness depends not only on their relative reactivity and concentration but also on their distribution between the phases. Interfacial polycondensation is conveniently done in two phase liquid systems of which one phase is water. The use of other liquids as a replacement for water was demonstrated.
Polybenzborimidazolines
Authors: Mulvaney J. E. , Bloomfield Jordan J. , Marvel C. S. 
Published: April 2003

AbstractThree new benzborimidazoline polymers have been prepared by condensation of aromatic diboronic acid derivatives and 3,3′‐diaminobenzidine. All of the polymers were soluble and had inherent viscosities in the range 0.1–0.35. The polymers prepared from benzene diboronic esters showed good thermal stability up to 500–600°C. A polymer prepared from ferrocene diboronic acid or ester began to decompose extensively between 300 and 400°C.
Kinetics of the thermal oxidation of butadiene–acrylonitrile copolymer
Authors: Beachell Harold C. , Spitsbergen James C. 
Published: April 2003

AbstractThe thermal oxidative degradation of an inhibited butadiene–acrylonitrile copolymer has been studied kinetically by means of infrared spectroscopy and color formation in the temperature range 100–200°C. In this type of degradation hydroxyl‐ and carbonylcontaining groups are formed from the decomposition of hydroperoxide or hydroperoxide radicals. The carbonyl groups are ketonic, resulting from a vinyl ketone initially formed by oxidative attack on the tertiary hydrogen and from a competing attack on α‐hydrogen. The interaction of the product of the latter competing reaction forms an intermediate, the decomposition of which requires an activation energy of 18 kcal./mole and yields a carbonyl and hydroxyl group. The radicals and hydroperoxides may also react to give either scission or aggregation. The oxidative products from these reactions give many types of oxygenated groups and radicals.
Effect of solvents on the molecular weight of polyacrylonitrile obtained by anionic catalysis
Authors: Zilkha Albert , Katz Y. 
Published: April 2003

AbstractThe effect of solvents on the molecular weight of polyacrylonitrile obtained by anionic polymerization with butyllithium was investigated. The molecular weight was found to decrease with increase in the dielectric constant of the solvents or their solvating power in the following order: petroleum ether « dimethylaniline > diethyl ether > tetrahydrofuran > dimethylformamide. The termination step of the polymerization is by chain transfer to monomer. The rate of propagation increases with increase in the dielectric constant, and the decrease in molecular weight seems to be due to a greater increase in the rate of termination. This lowering in molecular weight in anionic polymerization with increase in the dielectric constant is contrary to what is generally known in cationic polymerization, where, due to termination by the gegenion, the molecular weight increases.
Effects of hydrostatic pressure on boundary spreading in sedimentation velocity experiments
Authors: Billick Irwin H. 
Published: April 2003

AbstractThe effects of hydrostatic pressure on boundary spreading in sedimentation velocity experiments have been investigated, both theoretically and on a sample of polystyrene. A series of equations is given for obtaining the integral and differential distribution of sedimentation coefficients when pressure effects are present. These equations were derived on the basis of Fujita's mathematical treatment of the sedimentation of a monodispersed, pressure‐dependent system when diffusion and concentration effects are absent. Using these equations, distributions of sedimentation coefficients are calculated for a sample of polymer with a low polydispersity. The results obtained are compared with those obtained when pressure effects are neglected. The major change is a shift of the curve to higher sedimentation coefficient values, with a slight broadening of the distribution. However, it was found that the ratio of the weight‐average to number‐average molecular weight does not change appreciably.
Molecular weight distribution by velocity ultracentrifugation
Authors: Wales M. , Rehfeld S. J. 
Published: April 2003

AbstractA method is outlined for the determination of molecular weights and molecular weight distributions in linear, neutral polymers from boundary spreading data obtained from the ultracentrifuge. By use of the intrinsic viscosity, and having knowledge of its molecular weight dependence, it is possible to avoid calibration of the method with fractions of known molecular weight. Because of a maximum sensitivity of sedimentation coefficient to molecular weight, and only small concentration dependence of the sedimentation coefficient, theta solvents are preferred for these measurements. Corrections are made for pressure dependence of the sedimentation rate. The method is illustrated by measurements on polystyrenes in cyclohexane at 34°C. Comparison is made with precipitation chromatography data. Because of the number of experiments which must be made in order to extrapolate data to infinite dilution (each experiment consisting of at least four schlieren diagrams) this type of analysis probably involves as much labor as precipitation chromatography.
Polymer NMR spectroscopy. VI. Methyl methacrylate–styrene and methyl methacrylate–α‐methylstyrene copolymers
Authors: Bovey F. A. 
Published: April 2003

AbstractThe NMR spectra of methyl methacrylate–styrene and methyl methacrylate–α‐methylstyrene copolymers exhibit, among other features of interest, an unexpected multiplicity in the 6.4–7.8 τ region, characteristic of methoxyl protons. This multiplicity is believed due to magnetic shielding by styrene units. By comparing the results of a statistical analysis of monomer sequence probabilities with the relative areas of the methoxyl peaks, it is shown that the degree of shielding of the methoxyl protons is dependent not only upon the presence of styrene units as nearest neighbors along the chain but also upon their stereochemical configuration with respect to the methyl methacrylate units. By means of reasonable assumptions it is possible to explain the copolymer spectra and to give a partial description of the stereochemical configuration of the methyl methacrylate–styrene copolymers. The NMR method should be valuable in the analysis of other copolymers, particularly block and graft copolymers.
The molecular structure of polyethylene. XI. Weight‐ and number‐average molecular weights of selected samples
Authors: Kokle V. , Billmeyer F. W. , Muus L. T. , Newitt E. J. 
Published: April 2003

AbstractImproved methods for measuring weight‐ and number‐average molecular weight of polymers soluble only at elevated temperatures are applied to selcted samples of polyethylene. For two samples of essentially linear polyethylene, number‐average molecular weights by cryoscopy are 11,500 and 13,000, and weight‐average molecular weights by light scattering are 144,000 and 175,000. For samples of branched Fawcett‐type polyethylene, number‐average molecular weights are in the range 10,000–19,000 and weight‐average molecular weights are between 300,000 and 700,000. For one sample each of branched and essentially linear polyethylene it is demonstrated that light scattering measurement in three solvents gives the same molecular weight: no evidence is found for the “association” of these samples of polyethylene in thermodynamically poor solvents. It is thus demonstrated that association is not observed for all samples of polyethylene in dilute solution in α‐chloronaphthalene.
Molecular size distributions and average chain lengths of photodegraded polymer films
Authors: Jellinek H. H. G. 
Published: April 2003

AbstractExpressions for number size distributions and average chain lengths for initially homogeneous (one chain length only) polymer films photodegraded by random chain scission have been derived. Beer‐Lambert's law has been assumed to hold for the films. Numerical evaluations are given; errors due to treating the degradation process by the ordinary random theory of chain scission can become appreciable.
Polythiosemicarbazides. II. Effect of chemical structure on chelating properties. Structure of the chelates
Authors: Tomic Ernst A. , Campbell Tod W. , Foldi Veronika S. 
Published: April 2003

AbstractPolythiosemicarbazides react with acqueous Cu+2 solutions with formation of polymeric chelates, for which the following structure is typical:

The adsorption of Cu2+ by the polymer proceeds selectively and in preference to Fe3+, Zn2+, W6+, Al3+, Be2+, Cr3+, UO22+, Ni2+, V5+, Mo6+, Hf4+, Zr4+, Ta5+, Nb5+. Separations of these metals from Cu2+ are therefore possible.
Rheo‐optical studies of the nature of the α mechanical loss mechanism of polyethylene
Authors: Tanaka A. , Chang E. P. , Delf B. , Kimura I. , Stein R. S. 
Published: April 2003

AbstractDynamic x‐ray diffraction and dynamic birefringence techniques are employed to determine the nature of the molecular motions associated with the α mechanical loss processes for low‐density polyethylene. The results indicate that the low‐temperature part of this loss (designated α1) is associated with an interlammellar “grain boundary” slip process while the higher temperature process (α2) involves intracrystalline motion and plasticity of the crystal itself. The activation energy for α1 determined by x‐ray response is 25–30 kcal/mole, while that for α2 is 30–60 kcal/mole. The findings are consistent with dynamic infrared and dynamic light‐scattering results which indicate that the motion of amorphous chains is closely correlated with that of the crystals. The relative contributions of amorphous and crystalline regions to the birefringence are dependent on the thermal treatment of the sample. The effect of static strain on the dynamic response indicates that crystal orientability is first increased with strain, probably because of splaying apart of lamellae, is subsequently decreased because of the restrictions of interlamellae tie chains, but then increases again as the spherulites are destroyed at high strain. The static strain reduces the orientability of amorphous regions.
Statistics of configurational sequences in binary vinyl copolymers with asymmetric α‐carbon atoms
Authors: Gronski W. , Klesper E. 
Published: April 2003

AbstractThe configurational statistics, i.e., the distribution of isotactic and syndiotactic placements, of binary vinyl copolymers possessing asymmetric α‐carbon atoms is calculated for several sets of configurational parameters and three types of compositional statistics, i.e., Bernoullian, alternating, and blocklike. Terminal‐model copolymerization is assumed with only the last monomer unit of the growing chain having a kinetic influence on the addition of monomers, but not preceding monomer units or their configurations. The configurational statistics of the copolymer chains is non‐Markovian in general, which is in contrast to the first‐order Markovian character of the compositional chain. The magnitude of the deviation of the configurational statistics from the Bernoullian and first‐order Markovian distribution and the difference between configurational and compositional run numbers is evaluated. The degree of transcription of the compositional chain onto the configurational chain is discussed.
A model incorporating reversible immobilization for sorption and diffusion in glassy polymers
Authors: Tshudy James A. , Von Frankenberg Carl 
Published: April 2003

AbstractA model incorporating reversible, bimolecular immobilization for diffusion and sorption in glassy polymers is developed. Sorption is considered to occur by two distinct mechanisms: ordinary diffusion‐controlled sorption and sorption resulting from the immobilization of diffusing gas molecules by prexisting sites in the polymer. Expressions are obtained for equilibrium sorption, transient sorption, and time lag. The effects of kinetic parameters of the model are illustrated and discussed.
Polymerization systems engineering—a literature review
Authors: Fan L. T. , Shastry J. S. 
Published: April 2003

AbstractThis paper reviews research in the area of polymerization systems engineering. Polymerization systems engineering is divided into six subareas: thermodynamics, modeling and simulation, optimal reactor design, dynamic optimization, stability analysis, and optimal synthesis. Basic concepts of polymerization are presented, and research in these subareas is reviewed. It is concluded that much remains to be done.
Thermoelasticity of weak polyelectrolyte networks
Authors: Smith K. J. 
Published: April 2003

AbstractThe thermoelastic behavior of poly(vinyl alcohol)–poly(acrylic acid) networks was evaluated in pure water and CaCl2 solution. The ratio fe/f of the energy component of the force to the total force, evaluated without taking into account polymer–diluent specific interactions, ranged from −0.75 for networks swollen in pure water to −5.7 in 0.1M CaCl2. However, an analysis based on Flory's theory of polyelectrolyte gels yields fe/f constant at −1.32 when specific interactions are accounted for. In addition, the variation of In (r2)0 with CaCl2 concentration is 2000 times that with water. In neither pure water nor CaCl2 solution can specific interactions be neglected.
Inert gas permeation through homopolymer membranes
Authors: Lundstrom Jerry E. , Bearman Richard J. 
Published: April 2003

AbstractNew data are reported for the permeation of inert gases through polyethylene, polytetrafluoroethylene, and silicone and natural rubbers. Additional data are compiled from the literature. The relative solubilities of these gases are practically insensitive to chemical variations in the homopolymer. Hence variations in structure at the glass transition (Tg) and melting (Tm) temperatures that affect diffusion also unambiguously affect permcation. Consequently an equivalence results between permeation at a given temperature for different polymers and permeation at different temperatures for a given polymer. Although the diffusion coefficient changes continuously with temperature, the Arrhenius parameters Do and Ed apparently change discontinuously at Tg and Tm. Their magnitudes and variations with atomic weight reach maxima at about Tg. These data indicate a dependence of the classical correlation between Do and Ed on polymer properties. A perturbed diameter for the permeant, specific for each polymer, is proposed for correlating the Do and Ed data. This correlation makes the changes observed at Tg and Tm more perceptible.
Effect of crosslinking density on biaxial relaxation of SBR by using reduced variables
Authors: Arenz R. J. 
Published: April 2003

AbstractUse of reduced variables to account for the effect of crosslinking density νe in a styrene–butadiene rubber (SBR) system is demonstrated for general biaxial stress states. Recently published results from stress relaxation tests on five SBR vulcanizates crosslinked to different degrees by tetramethylthiuram disulfide were superposed by using νe as a reduction variable. The equilibrium shear modulus Ge calculated from the master relaxation curve at long reduced times was in satisfactory agreement with other results for SBR. The time‐axis shifts were related in a linear logarithmic manner to the crosslinking density but had a slope slightly less than values previously reported for elastomer systems.
Morphology and mechanical properties of crystalline polymers. III. Deformation of spherulites in polyethylene
Authors: Wang Tsuey T. 
Published: April 2003

AbstractThe behavior of individual spherulites on uniform deformation of bulk polyethylene is studied with a model consisting of a spherical spherulite and a homogeneous matrix having the properties of the polymer. On the basis of this model, the nonaffine or inhomogeneous deformation in the spherulite is found to be primarily due to the curvilinearly anisotropic property or, more specifically, the spherically isotropic property of the spherulite. In the case of uniaxial stretching, mechanical interactions between spherulites are also to some extent responsible for the microinhomogeneous deformation. Details of the predicted deformation mode are compared with experimental observations reported in the literature and reasonable agreement is attained between theory and experiment for lightly drawn samples.
Dilute solution characterization of a POLA polyester
Authors: Spatorico A. L. 
Published: April 2003

AbstractSamples of poly(4,4′‐isopropylidenediphenylene 1,1,3‐trimethyl‐3‐phenylindan‐4′,5‐ dicarboxylate) were fractionated by the column‐elution, temperature‐gradient technique. Selected fractions, covering a 10‐fold range of molecular weight, were shown to have narrow molecular weight distributions by gel‐permeation chromatography (GPC), i.e., M̄w/M̄n= 1.15 ± 0.10. The fractions were further characterized by viscometry, light scattering, and membrane osmometry. Characterization of the small samples (ca. 0.3 g) was facilitated by use of a low‐volume light scattering cell. This allows measurements of refractive increment, light scattering, and viscosity to be performed on as little as 50 mg of sample. Molecular weights estimated by the GPC‐viscometry technique were in good agreement with the values obtained by light scattering. Estimates of the perturbed coil dimensions (150–200 Å) were in satisfactory agreement with those observed experimentally. The polydispersities of the fractions, determined by osmometry and light scattering, were in fair agreement with GPC data; the latter are considered subject to less experimental uncertainty.
Structure of poly(N‐methyl laurolactam)
Authors: Shalaby S. W. , Fredericks R. J. , Pearce Eli M. , Wenner W. M. 
Published: April 2003

AbstractThe structure of poly(N‐methyl laurolactam) has been studied in the solid state and in solution. In oriented, annealed monofilaments, the chain exhibits a distorted extended planar zigzag conformation. Upon orientation, an increase in crystallinity and a slight shift of the large d spacing in the diffraction pattern to a higher value is observed. In the crystalline regions of the polymer, the amide groups are proposed to have the anti conformation, whereas the amorphous regions may consist of both the syn and anti forms. Differential scanning calorimetry and thermal mechanical analysis showed multiple melting endotherms which probably result from partial melting and reorganization of small, imperfect crystallites. In solution, nuclear magnetic resonance spectroscopy showed the presence of a conformational equilibrium of the syn and anti amide groups in the polymer chains. The effect of thermal and mechanical treatments on certain infrared group frequencies of the amide moieties was studied and correlated with other pertinent analytical data.
Effect of degree of crosslinking on the tearing energy
Authors: Fedors R. F. 
Published: April 2003

AbstractMuch recent work has been carried out on the tear behavior of elastomers, both filled and unfilled, especially by workers at the Natural Rubber Producer's Research Association. By use of a criterion for tearing involving the concept of the tearing energy, the effects of variables such as test temperature, test rate, specimen geometry, and chemical nature of the elastomer have been investigated. The one variable which has not yet been studied is the specific effect of changes in the degree of crosslinking on tear behavior. By use of data published in the literature on the smooth tear behavior of unfilled SBR vulcanizates, it is shown that these data can all be superposed onto a common response curve when the proper normalizations are applied.