bluuebunny/crossref_metadata_2025_split huggingface dataset:
Configurational characteristics of trans‐1,4‐polychloroprene: Experimental results on the unperturbed dimensions and their temperature coefficient
Authors: Sato Kyosaku , Eirich F. R. , Mark J. E. 
Published: April 2003

AbstractPolychloroprene [CClCHCH2CH2]x of approximately 95% trans‐1,4 stereochemical structure was prepared by low‐temperature emulsion polymerization. Fractions, obtained by liquid–liquid precipitations were studied in toluene solutions at 30°C by viscometry and osmometry. In addition, force–temperature measurements were carried out on networks of the polymer in the amorphous state. The results obtained on the polymer solutions indicate that the unperturbed dimensions of trans‐1,4‐polychloroprene are essentially the same as those of trans‐1,4‐polybutadiene of the same molecular weight. This observation, that substitution of a relatively large Cl atom for one of the methine H atoms in the trans‐1,4‐polybutadiene repeat unit has little effect on the chain dimensions, suggests that this increase in substituent size is offset by the fact that the length of a CCl bond is very much greater than that of a CH bond. The results obtained on the polymer networks indicate that the unperturbed dimensions of trans‐1,4‐polychloroprene decrease significantly with increasing temperature, as has also been reported for both trans‐1,4‐polybutadiene and trans‐1,4‐polyisoprene.
A study of helix formation in polydimethysiloxane by Raman scattering
Authors: Hartley A. J. , Shepherd I. W. 
Published: April 2003

AbstractDepolarization ratios ρ of the Raman bands due to CH3 stretching at 2907 cm−1 and the SiO skeletal mode at 491 cm−1 have been measured in polydimethylsiloxane gum as a function of temperature from 100°C to −45°C. Below 0°C the changes in p have been interpreted in terms of the formation of helical regions in the gum. The enthalpy of helix formation ΔH has been determined as 3200 ± 600 cal/mole. An upper limit on the entropy change, ΔS, of 16 ± 3 e.u./mole and minimum values of helix content at different temperatures have been found. The Raman spectrum of crystalline polydimethylsiloxane is presented.
Dilute solution properties of styrene–acrylonitrile and styrene–methyl methacrylate copolymers. I. Intrinsic viscosity–molecular weight relations
Authors: Reddy C. Rami , Kalpagam V. 
Published: April 2003

AbstractStyrene–acrylonitrile (St–AN) copolymers of three compositions—27.4 mole‐% (SA1); 38.5 mole‐% (SA2); and 47.5 mole‐% (SA3) acrylonitrile—and styrene–methyl methacrylate (St–MMA) copolymer (SM) of 46.5 mole‐% methyl methacrylate were prepared by bulk polymerization at 60°C with benzoyl peroxide as the initiator, and were then fractionated. The molecular weights of unfractionated and fractionated samples were determined by light scattering in a number of solvents. The [η] versus M̄w relations at 30°C were established for SA1, SA2, SM, and polystyrene (PSt) in ethyl acetate (EAc), dimethyl formamide (DMF), and γ‐butyrolactone (γ‐BL), and for SA3 in methyl ethyl ketone (MEK), DMF, and γ‐BL. Second virial coefficients A2 and the Huggins constant were determined. From values of A2 and the exponent a of the Mark–Houwink relation it is seen that the solvent power for samples SA1, SA2, and PSt is in the order EAc < γ‐BL < DMF, while for sample SA3 the solvent power is in the order MEK < γ‐BL < DMF. The solvent power decreases with an increase in AN content. The solvent power of the three solvents used for SM copolymer sample is practically the same within experimental errors. From the a values it is concluded that in a given solvent the copolymer chains are more extended than the corresponding homopolymers.
Localized flow birefringence of polyethylene oxide solutions in a two roll mill
Authors: Frank F. C. , Mackley M. R. 
Published: April 2003

AbstractExperimental observations are reported of the behavior of solutions between two rotating parallel rollers where the form of the flow field between corotating rollers corresponds to that of a col which has nonorthogonal asymptotes. The obliquity of the asymptotes of the flow gives a direct measure of the relative magnitude of the constituent pure shear and rotational components of the flow field.Flow birefringence observations of polyethylene oxide solutions between the corotating rollers show that molecular orientation is limited to a highly localized region near the “outgoing” asymptotic sheet of the flow field in accordance with the predictions of a “persistent extensional flow” analysis presented. Counterrotating rollers show no flow birefringence also as expected.The behavior of polymer solutions and Newtonian fluids are compared. With increasing strain rate using corotating rollers the obliquity of the asymptotes of the flow remains constant for the Newtonian fluid but changes significantly for the polymer solution.
Effects of swelling and annealing on the viscoelastic behavior of solution‐crystallized and melt‐crystallized samples of fractionated polypropylene
Authors: Inamura Isamu , Ochiai Hiroshi , Yamamura Hitoshi 
Published: April 2003

AbstractDynamic viscoelastic measurements, E′ and E″, were carried out on solution‐crystallized and melt‐crystallized samples of fractionated isotactic polypropylene over the temperature range of −100°C to 150°C. The molecular weight ranged from 1.26 × 104 to 1.77 × 105. The effects of swelling and annealing on the α and β peaks were more pronounced for the lower molecular weight fraction than for the higher one. It was found that both the untreated solution‐crystallized and quenched melt‐crystallized samples contain a fair amounts of a constrained amorphous phase in which the molecular motions were so depressed that the corresponding peak could be observed as the low‐temperature component of the α peak. These constraints on the molecular motions are considered to originate from the spatial restrictions imposed by the presence of the surrounding crystallities.
Determination of surface area of copolymer latex particles by surface tension measurements
Authors: Kloubek J. , Friml K. , Petříková S. , Krejˇí F. 
Published: April 2003

AbstractThe surface tension γ of four copolymer latices, of their respective serums, and of aqueous solutions of dispersant alone were measured at various dilutions. By extrapolating the surface excess of dispersant (calculated by the Gibbs adsorption equation) both at the aqueous solution surface and at the serum surfaces to 1/c = 0 (c being the bulk concentration of dispersant) the same limiting site area Alim per adsorbed molecule was determined. Amounts of dispersant adsorbed by copolymer particles at various dilutions were determined from differences between the known total concentrations of the dispersant in latex and in serum at the same γ. These values were then extrapolated to the maximum adsorption at 1/c = 0 in latex. The surface area of copolymer particles was determined therefrom by using Alim. The average particle radius calculated this way agrees reasonably well with electron microscope measurements. Thus it appears that the method for determining latex particle surface area by surfactant titration may be calibrated by means of the Gibbs adsorption equation, provided one uses Alim and not the site area at the critical micelle concentration of dispersant.
The specific heat of linear polyethylene after annealing at low temperatures
Authors: Sakaguchi Fumio , Mandelkern Leo , Maxfield John 
Published: April 2003

AbstractAfter annealing at low temperature, linear polyethylene displays an unusual feature in its specific heat curve. On heating, a maximum is observed just above the annealing temperature. The magnitude of this excess specific heat is dependent on the initial level of crystallinity and the temperature and time of annealing. The maximum does not reappear on subsequent cooling followed by rapid heating and represents the formation and disappearance of an unstable structure. These results can be interpreted as a crystallization‐melting phenomenon and are consistent with the wide‐angle x‐ray diffraction patterns. The optimum effects are observed in the β‐region (−50°C to 0°C) and could possibly lead to complications in interpreting other phenomena in this temperature range.
The coherent scattering law for dilute polymer solutions: “Two‐component” description
Authors: Gurol H. 
Published: April 2003

AbstractMori's projection operator technique using an extended two‐component description is applied to the study of the coherent scattering law for a dilute polymer solution. Starting with Kirkwood's generalized diffusion equation, an exact 2 × 2 matrix Langevin equation is obtained for the normalized density–density correlation function. The scattering law is then calculated using the Rouse limit. The one‐component and two‐component results are compared.
Adiabatic compressibility of solutions of ethylene–propylene copolymers in hydrocarbon solvents
Authors: Dunbar Janice I. , Pethrick Richard A. 
Published: April 2003

AbstractAdiabatic compressibility measurements are reported on solutions in hydrocarbon solvents of a low Mw high ethylene content, and of both high and low Mw low ethylene content ethylene–propylene copolymers. In all solutions the observed adiabatic compressibility was lower than the solvent value by an increment which was a function of the solvent type. Comparison of the data for a high and low molecular weight sample of the same copolymer indicates no molecular weight effects. Changes in the composition of the copolymer, as indicated by NMR spectroscopy, have only a slight effect on the adiabatic compressibility. The dominant feature of these studies is the apparent correlation of the chain length of the alkane solvent with the decrement in the compressibility.
Homopolymers: A theoretical study of neighbor‐group effects in repeated periodate oxidation of polysaccharides. I
Authors: Hemmer P. C. , González J. J. 
Published: April 2003

AbstractPeriodate oxidation of polysaccharides shows inhibitory neighbor effects due to hemiacetal formations. A second periodate oxidation may be performed after removal of all protecting hemiacetals formed in the first oxidation.We give the theoretical analysis of the kinetics of such repeated oxidations. For complete protection the oxidation limit of the second reaction, as function of the extent of the first oxidation, lies between 41.1 and 43.2%, in good agreement with experiments on alginate. For general protection effects we calculate the degree of oxidation and the mean sequence lengths of the three types of monomer units. Second‐oxidation data, in contradistinction to first‐oxidation results, allow separate determination of left‐and right‐hand inhibitory effects.
A new approach to analytical density gradient equilibrium centrifugation. Simultaneous determination of molecular weight, specific volume, and preferential hydration of human transferrin
Authors: Lundh Søren 
Published: April 2003

AbstractHuman transferrin was examined by analytical density gradient equilibrium centrifugation using a short liquid column and employing an iodinated organic gradient salt. Favorable conditions of low pressure and relatively low ionic strength could therefore be obtained. The short liquid column also permitted the layering of extra salt solution above the protein solution in a liquid equalization stage of each experiment. In this stage the amount of preferentially bound water was determined by measurement of solvation arising from the dissolution of the protein which had been added to the centrifuge cell as freeze‐dried material. Since schlieren optics were employed, the refractive index of the macromolecular component in the mixed solution had to be known. This quantity was determined from the refractive index difference of the solvent/solution boundary at the liquid equalization stage of each experiment or, alternatively, by regression analysis of the equilibrium data. The new regression method yielded an anhydrous molecular weight of 78,000 daltons which is the same as the value obtained by the classical density gradient equilibrium method performed under the same conditions. Control experiments showed that the analytical ultracentrifuge cell cannot be regarded as a closed, inert system.
Structural changes on hot‐rolling of polyethylene. II. Crystallite size distribution and lattice distortions
Authors: Yoda Osamu , Kuriyama Isamu 
Published: April 2003

AbstractThe crystallite size distribution and lattice distortion in the [100] direction in hot‐rolled high‐density polyethylenes have been obtained by the analysis of the 200 x‐ray line profile, using a Fourier transform technique. In the early stage of rolling (roll ratio <6) crystallite orientation is accompanied by breakup of crystallites due to intracrystallite slip, whereas in the heavily rolled stage (roll ratio ≧6) deformation proceeds through intercrystallite slip without degradation of crystallites. No marked change in lattice distortion can be found on hot‐rolling, at least up to a roll ratio of 8. This shows that the lattice distortion in the rolled sample relaxes to the same extent as in the original lattice when the sample is processed in the crystalline relaxation (αc) region.
Measurement of high chain extensions in polyethylene by gel permeation chromatography
Authors: Bassett D. C. , Khalifa B. A. , Olley R. H. 
Published: April 2003

AbstractChain extensions above 1000 Å have been measured in two independent ways for various linear polyethylenes which had either been annealed in or crystallized into the high‐pressure hexagonal phase. The distributions of fold‐stem lengths measured from fracture‐surface statistics and by gel permeation chromatography (GPC) molecular weight analysis of nitrated polymer agree reasonably well both in shape and position. Thinner lamellas, contributing to separate low melting peaks are, however, generally not recorded in fracture surfaces. The best agreement between the two measures, in their averages and overall distributions, is when the GPC weight distribution is compared with the number fracture‐surface histogram. This is explicable in terms of the details of nitration.
Conformational transitions of poly(β‐benzyl L‐aspartate)
Authors: Kyotani Hiroko , Kanetsuna Hisaaki , Ōya Masanao 
Published: April 2003

AbstractConditions that affect the conformation of poly(β‐benzyl L‐aspartate) in films have been studied. A slow transition from the left‐handed to the right‐handed α‐helical form is observed under certain conditions in half‐dried film cast from chloroform solutions and after exposure of amorphous films of the left‐handed β‐helical form to chloroform vapor. This transition is caused by adsorption of moisture. Thermal transitions of these films were examined by differential scanning calorimetry and infrared spectroscopy. The right‐handed α‐helices change to left‐handed ω‐helices around 140°C, and sharp exothermic peak is observed in this region for some films.
A probabilistic theory on the time to fracture of amorphous crosslinked polymers
Authors: Valanis K. C. , Yilmazer U. 
Published: April 2003

AbstractThe energy probability theory of fracture proposed by Valanis has been extended to apply to the global fracture of a large material region and has been generalized to take into account the probabilistic distribution among bonds of the free energy of the region. In contrast to the theory of fracture initiation of the first author, it is assumed, in the present paper, that global fracture is brought about by the fracture of a critical number Ncr of primary bonds. Whereas this condition alleviates some of the problems encountered in the application of the theory to fracture initiation and propagation—such as determination of the local energy field at the root of a developed crack—it introduces the difficulty that Ncr may, in general, depend on the geometry of the specimen and the directionality of the stress field, though it was found to be relatively insensitive to the rate of deformation, as corroborated in this paper. The theory is used in this work to predict the time of global fracture, under conditions of constant load, constant strain, and constant strain rate.
Heat conduction in a two‐dimensional spherulite
Authors: Galȩski A. , Milczarek P. , Kryszewski M. 
Published: April 2003

AbstractThe anisotropy of thermal conduction in a spherulite is calculated for a two‐phase model. The problem of the temperature distribution due to cooling of a spherulite suddenly heated at one point is solved. An analytical result is given and isothermal contours are calculated for wide ranges of thermal conduction anisotropy and cooling time. Experiments with spot‐heated isotactic polypropylene (i‐PP) and isotactic polystyrene (i‐PS) spherulites were conducted using a laser pulse and a needle as heat sources. The isotherms were recorded using a thin coating of a heat‐sensitive indicator substance, and then by comparison with theoretical isotherm patterns the heat conduction anisotropy of a PP spherulite was estimated. Additional measurements of heat conduction coefficients of at least two polymer films characterized by different crystallinity permit calculation of the thermal conductivity of the amorphous phase, and the conductivities of single crystals along chains and perpendicular to the chains. The results show that the heat is transferred mainly along the primary bonds of polymer chains. However, the morphology of sperulites and lamellas plays an important role.
Particle morphology in the early stages of radiation‐induced heterophase polymerization of vinyl chloride
Authors: Palma G. , Talamini G. , Tavan M. , Carenza M. 
Published: April 2003

AbstractInvestigations of the particle morphology of poly(vinyl chloride) produced under quiescent conditions during radiation‐induced bulk polymerization over the temperature range −30 to 70°C were carried out. The observations were mainly confined to the early stages of polymerization. For polymerization temperatures below about 20°C, the systems remain predominantly homogeneous during the entire polymerization and the polymer particles increase in size linearly with conversion. At higher temperatures the polymer particles rapidly settle and become cemented together. The findings are discussed in the light of the kinetic data on vinyl chloride polymerization, and a process of particle formation and growth, resembling that recently proposed by Fitch for emulsion systems, was formulated. Primary particles are initially formed by the coiling up of single macromolecules or single macroradicals and, subsequently, they increase in size by sweeping up growing free radicals from the liquid monomer phase. The free radicals which escape capture give rise to new primary particles, but their number progressively decreases as the number of the dispersed particles increases. Simultaneously, the polymer particles undergo flocculation which in a short time results in the formation of large agglomerates. As the volume of the resulting agglomerates increases, the flocculation rate decreases and, eventually, becomes so low that the flocculation does not proceed further. At low temperatures the flocculation almost ceases when the agglomerates are still small enough for sedimentation to occur only very slowly. However, this is not the case at higher temperatures. The addition of substances such as alcohols, brings about a reduction in the flocculation rate and, hence, in the size of the agglomerates formed at the end of the flocculation process. In this way, one can also obtain at high temperatures agglomerates of small sizes which remain dispersed for a long time.
Thermodynamics of plasticized triblock copolymers. I. Theory
Authors: Pico Efrain R. , Williams Michael C. 
Published: April 2003

AbstractThe thermodynamic theory of bulkABAcopolymers developed by Leary and Williams is extended to copolymer–solvent systems. Free energy expressions are derived for five hypothetical phase‐separated morphologies and evaluated specifically for a polymer with approximately 25% of theAcomponent. The separation temperature,Ts, at which a given morphology will be in equilibrium with a homogeneous mixture, is also evaluated. The major result is the prediction of theTs(ϕS) depression, where ϕs is the solvent fraction. Depression is maximized when δSis equidistant between δAand δB, but becomes rapidly less when δSis outside the δA–δBrange. Morphological favoritism is independent of ϕSand δS(model does not apply to preferential precipitation), with a planar microstructure being favored along with microstructures containing domains ofBin continuousAfor the 25%Apolymer.
Green's function analysis of the vibrational spectra of polymer chains. II. Fourier method for calculating the green's function of a perfect infinite polymer chain
Authors: Kozyrenko V. N. , Kumpanenko I. V. , Mikhailov I. D. 
Published: April 2003

AbstractA new method of calculating the Green's function (GF) for an arbitrary polymer chain is suggested. It makes it possible to obtain analytical expressions for this function in a number of cases of practical value.
Criterion for craze nucleation in polycarbonate
Authors: Ishikawa Masaru , Narisawa Ikuo , Ogawa Hiroyuki 
Published: April 2003

AbstractPlastic deformation and crazes were initiated in polycarbonate bars containing a round notch by three‐point bending. Morphological observations revealed that internal crazes are nucleated by a hydrostatic stress component caused by plastic constraint ahead of the fully developed plastic deformation zone. The characteristics of the deformation bands for quenched and slowly cooled materials are in good agreement with the logarithmic spiral curves predicted from a slip‐line theory. The distribution of the stress components in the plastic deformation zone was analyzed using this theory. The critical hydrostatic stress is 87 MN/m2 for slowly cooled polycarbonate and 89 MN/m2 for quenched material. These results are compared with those of the craze nucleation models of Gent and Argon.
Deformation mechanisms of constrained polymer chains. I. Geometrically induced correlations in the deformation response mechanisms of tie molecules
Authors: McCullough R. L. 
Published: April 2003

AbstractThe geometrical constraints acting on sections of tie molecules in noncrystalline regions severely limit the number and type of available polymer chain conformations. It is shown that these constraints induce explicit correlations in the rotations about the backbone bonds. These correlated rotations, in turn, specify distinct structural conversion paths which define the molecular mechanisms underlying the deformation response of tie molecules. Application of these constraining relationships to highly oriented polyethylene shows that the kink and jog structures of tie molecules can be decomposed into combinations of three primary conformational building blocks. Each of the basic conformational subunits follow an explicit set of dihedral angle correlations and, consequently, imparts specific characteristics to the composite structure of tie molecules. It is proposed that the composite response characteristics of tie molecules can be described as linear combinations of the response characteristics of these three primary conformational subunits.