bluuebunny/crossref_metadata_2025_split huggingface dataset:
Salt rejection by polymer membranes in reverse osmosis. II. Ionic polymers
Authors: Yasuda H. , Lamaze C. E. , Schindler A. 
Published: April 2003

AbstractThe water permeability K1 [which is related to water flux J1 per unit membrane area by J1 = K1(Δp − ΔII)/ΔX, where Δp is the pressure difference, ΔII is the osmotic pressure of feed solution, and ΔX is the membrane thickness] of homogeneous ionic polymer membranes in reverse osmosis and their salt rejection Rs [which is given by Rs ≡ 1 − (C2″/C2′), where C2′ is the concentration of the salt in feed solution, and C2″ is the concentration of salt in effluent] were examined with cationic and anionic membranes of block and graft copolymers. For ionic membranes, Rs and K1 are related by K1 = A exp { − BRs}, where A and B are constants. This equation was found to be independent of the ion charge, the chemical nature of the polymer, and film morphology. The principle of salt rejection by ionic membranes was explained by the difference in the transport volumes (volume elements available for transport) for mobile co‐ions and water. The electric repulsive force between a fixed ion and a mobile co‐ion decreases the transport volume of the latter, thus creating a transport depletion of salt flux relative to water transport. This transport depletion is governed by the amount of water sorbed by a fixed ionic site, which also determines the water flux. Consequently, Rs and K1 for ionically charged membranes are related as described above. This relation significantly differs from that found between Rs and K1 for nonionic polymer membranes, where the size and the solubility of ions in the membrane are mainly responsible for the transport depletion. The decline of Rs with increasing K1 is much less in ionic membranes than in nonionic ones; however, in the high Rs region, K1 for both ionic and nonionic membranes become similar as the dominant mode of water transport changes from flow to diffusion.
Characterization of moisture‐cured polyurethane films
Authors: Hassan A. M. , Ray L. N. 
Published: April 2003

AbstractA series of polyurethanes (PU) prepolymers with NCO/OH ratios of 2.1:1 and 1.9:1 were prepared by reacting hydrogenated methylene di‐p‐phenyl diisocyanate (HMDI) with triol mixtures of TP740 (molecular weight 740) and TP1540 (molecular weight 1540). Stress–strain (S/S) and swelling equilibrium measurements were performed using thin‐film samples prepared by moisture‐curing the prepolymer at room temperature. The swollen PU networks gave an S/S curve which is fully described by rubber elasticity theory. The Mooney‐Rivlin constant C1 (swollen) was found to increase directly while the molecular weight between crosslinks Mc decreases as the number of branches per cubic centimeter is increased. The solvent—polymer interaction parameter χ determined in benzene was 0.077 + 0.97vr, where vr is the volume fraction of rubber in the swollen network. The crosslink density v′, and Mc were calculated from the relations v′ = pNB and Mc = 0.667 B−1, where B denotes moles of branches per gram, and were found to be in good agreement with v′ and Mc established from S/S and swelling‐equilibrium measurements. In calculating v′ and Mc, the water‐PU crosslinking reaction at room temperature was assumed to occur mainly through the formation of a urea linkage.
Reaction kinetics in dilute solutions of chain molecules carrying randomly spaced reactive and catalytic chain substituents. II. Dependence of the ring closure probability on the solvent medium and the nature of the chain backbone
Authors: Goodman Neil , Morawetz Herbert 
Published: April 2003

AbstractTernary copolymers of acrylamide or methacrylamide with small proportions of comonomers carrying reactive p‐nitrophenyl ester and catalytic pyridine groups in the side chains were prepared. The kinetics of the ester solvolysis was followed in highly dilute solutions, so that the rate was controlled by interaction of groups carried by the same chain backbone. Data were obtained in water and aqueous methanol and were interpreted by a computer simulation procedure in terms of the dependence of the probability of encounter between two chain substituents on their spacing along the chain backbone. This probability decreased more slowly with increasing separation of the interacting groups when the solvation of the polymer was reduced, but even in solvents approaching θ conditions the results deviated from theoretical predictions for chains without excluded volume. The formation of cyclic conformations is considerably more difficult in methacrylic than in acrylic chains, although the chain flexibility, as characterized by unperturbed chain dimensions, is very similar in the two systems.
Effect of molecular weight on the refractive increment of polyethylene and n‐alkanes
Authors: Wagner H. L. , Hoeve C. A. J. 
Published: April 2003

AbstractAs in the case with other polymers previously reported, the values of the refractive index increment dn/dc of polyethylene and the n‐alkanes change with molecular weight. Most of the variation may be understood by examination of the role of density in the Lorentz‐Lorenz mixing equation for specific refractivity, R12 = p1R1 + P2R2 used to calculate dn/dc. It may also be shown that as the absolute refractive index difference between solute and solvent becomes smaller, dn/dc becomes more sensitive to density change of the solute.
Fold surface of polyethylene single crystals as assessed by selective degradation. I. Ozone degradation method
Authors: Priest D. J. 
Published: April 2003

AbstractOzone has been used as a selective oxidizing agent for degrading polyethylene single crystals at room temperature in order to confirm and extend results on surface structure obtained by use of fuming nitric acid at temperatures above 60°C. The surfaces of the crystals were rendered highly accessible to the ozone gas by preparing the crystalline material in a highly expanded form; the solvent in which the crystals were suspended was removed by sublimation from the solid state. The extent and nature of the reaction were studied by measuring the increase in weight and in density, by direct chemical analyses, and by making use of infrared spectroscopy and gel‐permeation chromatography. It was found that the surfaces of the crystals are attacked at room temperature by ozone, with resulting chain scission, and the broad features of the chemical reaction were established. Some folded chains are found to be as long as the original thickness of the crystal, and once folds have been cut, continuing reaction shortens the chains. In the early stages of the degradation, during which most of the weight increase takes place, the density of the crystals increases, and the magnitude of the increase is that expected from the increase in weight alone, i.e., assuming no increase in effective volume.
Steady flow and dynamic viscosity of branched butadiene–styrene block copolymers
Authors: Kraus Gerard , Naylor F. E. , Rollmann K. W. 
Published: April 2003

AbstractSteady flow and dynamic viscosities were determined for symmetrical linear and starbranched block copolymers of butadiene and styrene above their upper (polystyrene) glass transition. Block structures examined were B‐S‐B, (B‐S‐)3, S‐B‐S, (S‐B‐)3 and (S‐B‐)4. At constant molecular weight and total styrene content viscosities were greater for polymers terminating in styrene blocks, irrespective of branching. Branching decreased the viscosity of either polybutadiene‐terminated or polystyrene‐terminated block polymers, compared at equal Mw. However, comparisons at equal block lengths showed that the length of the terminal blocks, not the total molecular weight, governs the viscoelastic behavior of these polymers to a surprisingly good approximation. This unusual result is rationalized in terms of the two‐phase domain structure of these polymers, which persists to a significant degree in the melt. Below the glass transition of the polystyrene blocks the effects of branching were masked by differences in the morphology of the domain structure unrelated to branching.
Study of compositional distribution in a styrene–methyl acrylate copolymer by means of density‐gradient centrifugation
Authors: Nakazawa A. , Hermans J. J. 
Published: April 2003

AbstractSeveral samples of a copolymer were examined by means of equilibrium centrifugation in a density gradient. The results for the samples without compositional distribution (homogeneous polymers) were used to determine the relation between the chemical composition and the distance from the center of rotation. For one of the homogeneous polymers a quantitative analysis of the schlieren curve was made in order to show the kind of accuracy that can be achieved. For the inhomogeneous polymer it was found that the schlieren curve could, in principle, be described quantitatively by the assumption that fluctuations in composition are independent of fluctuations in molecular weight, but on this basis the average square of the fluctuations in composition is more than four times smaller than the value derived from chromatographic data. A more satisfactory explanation of the experimental results is provided by assuming a linear correlation between average molecular weight and composition, but it is not claimed that this is necessarily the only model that explains the data.
Emulsion polymerization of styrene in a single continuous stirred‐tank reactor
Authors: DeGraff Andrew W. , Poehlein Gary W. 
Published: April 2003

AbstractThe effects of mean residence time, initiation rate, and emulsifier concentration on particle formation, particle growth, and polymerization rate are examined for the emulsion polymerization of styrene in a completely mixed continuous stirred‐tank reactor. Experimental measurements of number of particles, particle size distribution, polymerization rate, and molecular weights are compared with theoretical predictions. A theoretical model which incorporates Stockmayer's modification of the Smith‐Ewart theory into the particle growth equation allows reasonably accurate prediction of polymerization rate, particle formation rate, and particle size distribution. Agreement between experimental measurements of number‐average and weight‐average molecular weights and a theory based on Smith‐Ewart case 2 kinetics is also reasonable.
Dynamic mechanical properties of moderately concentrated polystyrene solutions
Authors: Holmes Larry A. , Kusamizu Sumio , Osaki Kunihiro , Ferry John D. 
Published: April 2003

AbstractThe storage (G′) and loss (G″) shear moduli have been measured in the frequency range from 0.04 to 630 Hz for solutions of narrow distribution polystyrenes with molecular weights (M) 19,800 to 860,000, and a few of poly(vinyl acetate), M = 240,000. The concentration (c) range was 0.014–0.40 g/ml and the viscosities of the solvents (diethyl phthalate and chlorinated diphenyls) ranged from 0.12 to 70 poise. Data at different temperatures (0–40°C) were combined by the method of reduced variables. Two types of behavior departing from the usual frequency dependence describable by the Rouse‐Zimm‐Tschoegl theories were observed. First, for M ≅ 20,000, the ratio (G″ − ωηs)/G′ in the neighborhood of ωτ1 = 1 was abnormally large and the steady‐state compliance J was abnormally small, especially at the lowest concentrations studied. Here ω is circular frequency, ηs solvent viscosity, and τ1 terminal relaxation time. Related anomalies have been observed by others in undiluted polymers at still lower molecular weights. Second, at the highest concentrations and molecular weights, a “crossover” region of the logarithmic frequency scale appeared in which G″ − ωηs < G′. The width of this region is a linear function of log c; the frequency dependence under these conditions can be represented by a sequence of Rouse relaxation times grafted on to a sequence of Zimm relaxation times. For each molecular weight, the terminal relaxation time τ1 was approximately a single function of c for different solvents of widely different ηs. At lower concentrations, τ1 was close to the Rouse prediction of 6ηM/π2cRT, where η is the steady‐flow viscosity; but at higher concentrations, τ1 was proportional to η/c2 and corresponded, according to a recent theory of Graessley, to an average molecular weight of 20,000 between entanglement coupling points in the undiluted polymer.
Glass transition in ionic polymers: The acrylates
Authors: Eisenberg A. , Matsura H. , Yokoyama T. 
Published: April 2003

AbstractIt is shown that the glass transition temperatures of the ionic acrylates are subject to the same correlation as found for the phosphates, silicates, and ionenes; the equation is Tg = 730 (q/a) − 67, where q is the cation charge and a the separation between centers of charge for the cation and anion.
Small‐angle light scattering from optically anisotropic spheres and disks. Theory and experimental verification
Authors: Samuels Robert J. 
Published: April 2003

AbstractThe small‐angle light scattering (SALS) theory for optically anisotropic spheres and disks is examined in depth. An error is found in the existing sphere equations. The correct form of the equations is identified and then experimentally verified for dilute starch suspensions. Increased concentrations and solid films of starch granules are used to identify the effect of concentration on the scattering envelope. Spherulitic films of isotactic polypropylene, isotactic polystyrene, nylon 610, PET, and nylon 66 are then used to examine different aspects of the SALS theory. Experimental observations are found to agree with the predictions of the correct SALS equations. Disk theory is interrogated and correlated with predictions for spheres. It is found that the predicted patterns from spheres and disks are very similar under identical optical conditions, in contradiction to earlier predictions. A method is developed for identifying the optical sign of spherulites too small to be seen in the optical microscope. This study constitutes a comprehensive examination of SALS theory and includes many other aspects of the phenomena. A catalogue of theoretical Vv SALS patterns from spheres and disks is also included.
Synthesis of polyimides by photoaddition of bismaleimides to benzene
Authors: Musa Yusuf , Stevens Malcolm P. 
Published: April 2003

AbstractPolyimides have been synthesized by the sensitized photoaddition of aliphatic and aromatic bismaleimides to benzene. The reaction involves 2+2 cycloaddition to give homoannular diene intermediate followed by Diels‐Alder addition to give polymer. Proof of structure is based mainly on a comparison of infrared spectra with those of the corresponding polyimides prepared from maleic anhydride‐benzene photoadduct and diamines. The very low solubility of the polymers indicates that crosslinking probably occurred during photolysis. All the polyimides appear to decompose by decyclization at about 420–485°C. Polymer yield was dependent on bismaleimide structure.
Organometallic polymers. XVI. Copolymerization of styrenetricarbonylchromium and the reaction of polystyrene with chromium hexacarbonyl
Authors: Pittman Charles U. , Grube Paul L. , Ayers Orval E. , McManus Samuel P. , Rausch Marvin D. , Moser Glenn A. 
Published: April 2003

AbstractStyrenetricarbonylchromium (IV) has been synthesized. Monomer IV did not homopolymerize with free‐radical initiation but copolymerized with styrene, methyl acrylate, and vinylcymantrene. The copolymerizations were carried out in benzene solutions at 70°C with azobisisobutyronitrile as the initiator. The relative reactivity ratios were determined for the styrene and methyl acrylate copolymerizations. They were (defining M1 as monomer IV) r1 ≅ 0, r2 ≅ 1.39 for styrene copolymerizations and r1 ≅ 0, r2 ≅ 0.75 for methyl acrylate copolymerization. Polystyrene reacted with chromium‐hexacarbonyl in refluxing DME to produce a polymer in which about 32% of the benzene rings were complexed with Cr(CO)3 units. The use of a polystyrene of narrow molecular weight distribution in this reaction demonstrated that no decomposition of the polystyrene chains occurred.
Effects of high pressure on the conductivity and dielectric constant of conductive organic polymers
Authors: Pohl Herbert A. , Wyhof John R. 
Published: April 2003

AbstractPrevious theory for pressure effects on conduction in amorphous macromolecular solids is extended to include pressure effects on hyperelectronic polarization. A theoretical estimate of hopping activation energies is given. Experimental studies of the frequency effects of the pressure coefficients of conduction and permittivity permits resolution of the salient factors. Carrier mobility in ekaconjugated polymers is best represented by activated hopping, for conductivity increase with frequency, and permittivity drops. Conductivity and hyperelectronic polarization increase markedly with pressure. Their activation energies, Ea0, and the pressure coefficients of their activation energies (bE + bH) are nearly identical. Ea0 is frequency‐dependent, but the (bE + bH) terms are not, showing the frequency dependence of Ea0 to lie in the hopping activation enthalpy. Similar arguments on the “total” pressure coefficients b and b for conduction and polarization show the latter coefficients to have a frequency dependence lying in the hopping activation entropy.
Solution properties of ethylene‐vinyl acetate copolymers
Authors: Salyer I. O. , Kenyon A. S. , Ohta M. 
Published: April 2003

AbstractHigh‐pressure ethylene–vinyl acetate copolymers of four different chemical compositions(9%, 15%, 45%, and 70% VA) were characterized to determine molecular weight and distribution. The four samples were fractionated by solvent–nonsolvent precipitation methods. Light‐scattering, osmometry, and viscosity measurements were made on these fractionated copolymers to determine weight‐average molecular weight \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {M_w } $\end{document}, number‐average molecular weight \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {M_n } $\end{document}, molecular size in solution, and interaction constants. Dilute solution viscosity was measured on the fractions to determine intrinsic viscosity and Huggins' constant k′. Viscosity–molecular weight equations were established for the four copolymer compositions. The log intrinsic viscosity versus log molecular weight diagrams were analyzed and the average length of branches calculated. The composition of the polymer fractions, determined by C and H combustion analysis, was found not to vary significantly with molecular weight. The uniformly random character of the E/VA copolymers was thereby confirmed. The density of the fractions was determined by density‐gradient column method. Chain sequence distribution of monomer units for the four copolymers was calculated by using IBM 704 computations involving the actual monomer reactivity ratios. Long sequences of either ethylene or vinyl acetate are improbable, except at the extremes of copolymer composition.
Effect of fluid‐phase equilibria on ethylene‐vinyl acetate copolymer composition
Authors: Leder F. , Wisotsky M. J. 
Published: April 2003

AbstractLiterature reports indicate that in the copolymerization of ethylene with vinyl acetate, the reactivity ratios change with pressure. There is general agreement that reth ≅ rvac ≅ 1 at high pressure, but deviations reportedly occur at low pressure. It is shown here that this “pressure dependence” in fact arises from a failure to recognize adequately the importance of fluid‐phase equilibria in the ethylene–solvent system. In order to delineate the two‐phase region, the ethylene–benzene critical locus was measured from the ethylene critical point to 125°C. It was found that the maximum pressure was at about 1700 psia. Above the critical locus the two components are miscible in all proportions, forming a single homogeneous phase. As predicted by phase rule considerations, ethylene‐vinyl acetate copolymers prepared at constant temperature and pressure below the critical locus had fixed compositions. Copolymerizations conducted above the critical locus were not similarly constrained, and polymer compositions varied with operating procedure. This phenomenon is best understood in light of degrees of freedom afforded by the fluid phase equilibria. In either fluid regime the reactivity ratios are shown to be unity and independent of pressure. This was demonstrated at pressures as low as 50 atm.
Cis/trans copolyamides of 1,4‐bisaminomethylcyclohexane
Authors: Prince Frank R. , Turi Edith A. , Pearce Eli M. 
Published: April 2003

AbstractCopolyamides prepared from cis‐ and trans‐1,4‐bisaminomethylcyclohexane with adipic, sebacic, and dodecanoic acids showed a decrease in melting point with increasing cis diamine content and increasing chain length of the diacid. Most unusual was the fact that the glass transition temperature of these copolymers were essentially independent of diamine isomer content. The existence of an intermediate conformation for some of the cyclohexane rings such as the “twistmer” is suggested to account for this discrepancy. The Tg, Tc, and Tm all decreased with increasing chain length of the diacid. The thermal stability as exemplified by the polysebacamides, was independent of diamine isomer content.
Polymers containing 12‐hydroxymethyltetrahydroabietanol
Authors: Bingham John F. , Marvel C. S. 
Published: April 2003

Abstract12‐Hydroxymethyltetrahydroabietanol has been polymerized with hexamethylene diisocyanate and a low molecular weight polyurethane produced. Low molecular weight polyurethanes have also been prepared from 12‐hydroxymethyltetrahydroabietyl chloroformate, hexamethylenediamine, and sym.‐dimethylethylenediamine. 12‐Hydroxymethyltetrahydroabietanol has been “end‐capped” with tolylene‐2,4‐diisocyanate and hexamethylene diisocyanate. The resulting diisocyanates have been polymerized with polytetramethylene glycol, hexamethylenediamine and hydrazine.
Polyamides from 12‐(β‐aminoethyl) abietan‐18‐amine
Authors: Bingham John F. , Marvel C. S. 
Published: April 2003

AbstractThe 1:1 salt of 12‐(β‐aminoethyl)abietan‐18‐amine and adipic acid has been prepared and polymerized. This salt has been copolymerized with the 1:1 salt of hexamethylenediamine and adipic acid. 12‐(β‐Aminoethyl)abietan‐18‐amine has been polymerized with isophthaloyl and terephthaloyl chlorides with triethylamine as catalyst and terpolymerized with terephthaloyl chloride and hexamethylenediamine. All polymers have been characterized to some extent, and mechanical properties are reported for two of the polyamide films.
Polymerization of 3,3‐dimethyl selenetane
Authors: Goethals E. J. , Schacht E. , Tack D. 
Published: April 2003

Abstract3,3‐Dimethyl selenetane has been polymerized under the influence of different cationic and anionic catalysts. Cationic polymerization led to limited conversions because of the occurrence of a termination reaction between the growing chains and the formed polymer. The obtained polymers had low molecular weights. Anionic polymerization gave polymers with molecular weight up to 35,000. The mechanisms of polymerization are believed to be analogous to the mechanisms proposed for the polymerization of thietanes.
Polymerization of diphenylamine with friedel‐crafts/oxidation catalysts to produce thermally stable polymers
Authors: Ellis Bryan , Stevens J. V. 
Published: April 2003

AbstractThe synthesis of polymers from diphenylamine by use of ferric chloride and aluminum chloride–cupric chloride catalyst–oxidant systems has been studied. Optimum conditions for yield and thermal stability were determined for the aluminum chloride–cupric chloride systems. Thermal stabilities in air were between 450 and 500°C. Infrared and ultraviolet spectra indicate that reaction has taken place by direct nuclear coupling.