bluuebunny/crossref_metadata_2025 huggingface dataset:
Dipole moments in oriented poly(ethylene terephthalate)
Authors: Hsu Bay‐Sung , Kwan Sik‐Hung , Wong Lai‐Wah
Published: April 2003

Dielectric 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

In 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

It 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

It 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

X‐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

Complete 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

The 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

Individual 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.
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

Polychloroprene [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

Depolarization 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

Styrene–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

Experimental 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

Dynamic 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

The 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.
A method for the evaluation of the activation energy from relaxation experiments
Authors: Solunov Ch. , Ponevsky Ch.
Published: April 2003

A method is proposed for calculating the activation energy over the entire temperature range from relaxation measurements at two frequencies as a function of temperature by taking into account the entire experimental curve. The method is independent of the distribution of relaxation times, but assumes the validity of the time‐temperature superposition principle.
The specific heat of linear polyethylene after annealing at low temperatures
Authors: Sakaguchi Fumio , Mandelkern Leo , Maxfield John
Published: April 2003

After 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

Mori'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

Adiabatic 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

Periodate 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

Human 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

The 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

Chain 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

Conditions 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

The 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

The 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

Investigations 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

The 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

A 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

Plastic 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

The 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.
Multiblock copolymers of styrene and isoprene. II. Microstructure and dilute solution properties
Authors: Corbin N. , Prud'Homme J.
Published: April 2003

Dilute solution properties of linear (SI)3 six‐block copolymers of styrene and isoprene are compared to those of random, two‐block, and three‐block copolymers of the same system. All the copolymers were prepared with sec‐butyllithium in benzene. The microstructure of the polyisoprene blocks is close to that of homopolyisoprene prepared under the same conditions. In contrast, the random copolymer shows a larger amount of trans‐1,4 isoprene units. The intrinsic viscosities of the copolymers in methylisobutyl ketone, a poor solvent for both polystyrene and polyisoprene, and in toluene, a good solvent for both homopolymers, are examined on the basis of the Fox–Flory relation for homopolymers. All the copolymers behave similarly in each solvent. In methylisobutyl ketone, the viscosity results indicate a random coil conformation with a small expansion owing to the extra repulsive interactions between the dissimilar units. In all cases, the heterocontact repulsive interactions are small and can be characterized by an interaction parameter χab close to 0.025. In toluene, the perturbation caused by the heterocontacts becomes negligible and the expansion factor αη can be predicted from a weighted average of those of the parent homopolymers of the same molecular weight as the copolymer.
Low‐temperature relaxations in styrene‐crosslinked polyester networks. II. The γ′ relaxation
Authors: Cook Wayne D. , Delatycki O.
Published: April 2003

The low‐temperature γ′ relaxation was found to originate in the diol units of a variety of crosslinked polyesters. The results were explained in terms of Boyer's Crankshaft model. As the polyester concentration in the networks increased, the γ′ relaxation shifted to higher temperatures and the intensity of the relaxation increased but not as rapidly as the diol concentration. This behaviour was interpreted in terms of an interaction of the relaxing species with the surrounding matrix.
Selective degradation of nylon 6,6. I. Description of the degradation technique and preliminary morphological characterization
Authors: Hughes Alfred J. , Bell James P.
Published: April 2003

A technique for the selective degradation of amorphous regions in nylon 6,6 is reported. Samples of unoriented film and single‐crystal mats have been subjected to selective degradation by refluxing in hydrazine. Weight loss, viscosity‐average molecular weight, density, and small‐angle x‐ray scattering of these samples were monitored as a function of time of degradation. In addition, selected samples have been investigated by gel permeation chromatography (GPC) and transmission electron microscopy. Based on the results of these investigations it is concluded that the reported degradation technique is unique in that the debris is not monodisperse in molecular weight distribution. The Weight loss, density, small‐angle x‐ray scattering, and microscopy data demonstrate that the unordered or noncrystalline regions of the material are removed upon treatement. However, the relatively high molecular weight and broad molecular weight distribution of the debris indicate that regular folds at lamellar surfaces are intact after degradation treatment.
Low temperature relaxation in polypyromellitimide
Authors: Tanaka Takao , Shibayama Kyoichi
Published: April 2003

The effect of heat treatment at temperatures above 300°C on the low temperature relaxation of poly(4,4′‐oxydiphenylenepyromellitimide) (Kapton H‐film) was studied by wide‐line nuclear magnetic resonance (NMR), mechanical, and dielectric measurements. In the NMR line spectrum of the as‐received film, a narrow component above −60°C and a broad component which begins to narrow at about −100°C were observed. It is proposed that the narrow component is associated with absorbed water, because it disappeared in the heat‐treated film at 300°C in N2. On the other hand, the behavior of the broad component was not influenced by heating to 300°C in N2. Mechanical and dielectric loss peaks were observed at −75°C (11 Hz) and −65°C (1 kHz), respectively, in the as‐received film. These loss peaks did not change in intensity with heating to 300°C in N2. It is proposed that the mechanical and dielectric loss peaks corresponding to the narrowing of the NMR broad component are associated with the local‐mode motion of the diphenylether portion of the polypyromellitimide chain. It was found that crosslinks are formed by heating to 374°C in air through coupling of the diphenylether portions of the molecular chains. With the formation of crosslinks the dielectric loss peak shifted toward higher temperature and the intensity decreased through restriction of the local‐mode motion of the diphenylether portion of the molecular chain.
Radiation chemistry of polyethylene. XIV. Allyl radical decay kinetics in different types of polyethylene
Authors: Patel V. M. , Patel G. N. , Gvozdic N. , Hsu C. S. , Dole Malcolm
Published: April 2003

The decay kinetics of the chain allyl free radical has been studied in the following morphological forms of polyethylene (PE): Marlex bulk film, hydrogenated PE, and extended‐chain PE. Coupled with previous work on single‐crystalline PE it can be seen that the decay rate is greater the more amorphous the sample. In the Marlex bulk film and hydrogenated PE the decay can be interpreted in terms of a simultaneous fast and slow decay process by means of our Q‐function equation, but with rising temperature the decay approximates a single rate process. With extended‐chain PE the allyl decay rate does not become appreciable until the melting range is approached. The fraction of allyl radicals decaying by the slow process is 2 to 10 times greater than the fraction of fast decaying radicals. The ratio of the fast decay rate constant to that of the slow rate constant is greater for the bulk Marlex film than for the hydrogenated PE. All ratios decrease with rising temperature. For times up to about 150 min the allyl decay in the extended‐chain PE accurately follows a single second‐order decay law with a time‐independent diffusion controlled reaction rate constant.
Dependence of cooperative relaxation of amorphous polymers on diluent concentration
Authors: Havlíček I. , Ilavský M. , Hrouz J.
Published: April 2003

The Adam–Gibbs molecular theory, which describes the temperature dependence of relaxation phenomena in the main transition region in terms of the configurational entropy of a system, has been extended to include the effect of concentration of a low‐molecular‐weight compound on the viscoelastic behavior of concentrated polymer solutions. The concentration dependence of relaxation times in the polymer–diluent mixture leads to an expression of the concentration dependence both of the shift factor in the Williams–Landel–Ferry (WLF) equation and of the glass transition temperature Tg of the mixture. The constants of the WLF equation and the concentration dependence of Tg are given in terms of a difference between the specific heats of the liquid and glass ΔCp of the equilibrium temperature T2 of the second‐order transition, and of the parameter Δμs/k, which includes the chemical potential Δμ and the configurational entropy s of the smallest cooperatively rearranging region. The resulting relationships also predict the temperature dependence of the constants of the concentration WLF equation. Good agreement was found between theory and the viscoelastic and Tg data on the systems poly(vinyl acetate) + diethyl phthalate, poly(methyl methacrylate) + diethyl phthalate and polystyrene + dibutyl phthalate. This finding indicates that the configurational entropy, at least in the first approximation, is responsible for the concentration dependence of relaxation phenomena in concentrated polymer solutions.
Dielectric loss of high‐density polyethylene below 4.2°K
Authors: Yano Okimichi , Kamoshida Takaya , Sekiyama Shigehiro , Wada Yasaku
Published: April 2003

Drawing of oxidized high‐density polyethylene (HDPE) and subsequent annealing greatly reduce the low‐temperature dielectric loss when the electric field is applied perpendicular to the draw direction. This supports our model (J. Polym. Sci. Polym. Phys. Ed., 15, 43 (1977)) of the proton moving parallel to the c axis of the PE crystal. A particular antioxidant (Ionox 330) in unoxidized HDPE induces a dielectric loss with a frequency and temperature dependence which differs from that for the loss in oxidized HDPE. The antioxidant loss seems to be an overlapping of tunneling and a thermal activation process. The possibility that the hydroperoxide group in the PE crystal is the origin of the loss in oxidized HDPE was theoretically examined in a manner similar to that used for the hydroxyl group in the previous paper. Results suggest that the hydroperoxide group is less probable than hydroxyl as the origin of the low‐frequency loss in HDPE.
Influence of pressure and chemical structure on the thermal conductivity of vitreous poly(alkyl methacrylates). II. Relation to free volume
Authors: Frost R. S. , Barker R. E. , Chen R. Y. S.
Published: April 2003

A quantitative model for the pressure dependence of the thermal conductivity K in glassy polymers is presented. By extending the hole theory of liquids to temperatures below the glass transition temperature, an equation of state is obtained and an expression for the pressure dependence of the thermal conductivity is then formulated from a consideration of the anharmonicity associated with the segmental vibrations. The resulting equation ΔK/K = γGf0[1−exp(−p/B*)], where γG is the Grüneisen parameter, f0 is the fractional free volume, and B* = kTg/V0, is compared with experimental results for the poly(alkyl methacrylates).
Concentration and temperature dependence of the refractive index increment of a polystyrene sample in trans‐decalin
Authors: Roots Jaan , Nyström Bo
Published: April 2003

The refractive index increment of macromolecules in solution has been observed to be a function of concentration, temperature, molecular weight, wavelength of light, and solvent. Most of the studies have been performed in dilute or semidilute solutions, and therefore the concentration dependence of the refractive index increment was too small to be accurately observed. This study was performed on solutions of polystyrene in trans‐decalin at mass fractions, w2, from 0.01 to 0.11 and at 436 and 546 nm wavelengths. The concentration and temperature dependence of the refractive index increment were measured, and comparisons were made with previous theories.
Fine structure of polyethylene prepared by γ‐ray‐induced polymerization in various solvents. III. Selective degradation with ozone
Authors: Arai Hidehiko , Yamaguchi Koichi , Mitomo Hiroshi , Kuriyama Isamu
Published: April 2003

Ozone‐degradation products of polyethylenes prepared by γ‐ray‐Induced polymerization in ethyl alcohol, t‐butyl alcohol, and 2,2,5‐trimethylhexane were analyzed by gel permeation chromatography (GPC). The ozonized polymers show two discrete peaks in the GPC traces, and the ratio of molecular weights corresponding to the peaks is close to 1:2, suggesting that these polymers are composed of folded‐chain crystals similar to solution‐grown single crystals. The peak profiles, however, are broad and the peaks in the chromatograms shift concertedly toward lower molecular weight in the course of degradation. These findings suggest that the fold surfaces of the polymers are coarse and that there is no unique crystalline core containing a regularly folded layer. The long period estimated from small‐angle x‐ray measurements increases with increasing polymerization temperature, but scarcely varies with the solvent type. This implies that when crystallization occurs during polymerization, kinetic factors may have no great effect on crystallization.
Conformation of poly(isoprene‐gstyrene) in dilute solution
Authors: Hadjichristidis N. , Roovers J.
Published: April 2003

A detailed description of the synthesis of a model poly(isoprene‐g‐styrene) is given. From light scattering measurements the real radius of gyration of the polyisoprene is backbone is found to be smaller than that of the polystyrene branches. The core‐and‐shell conformation of graft copolymers in dilute solution in good solvents, which was proposed for poly(styrene‐g‐isoprene), is supported by these results.
Infinite‐dilution viscoelastic properties of sodium poly(styrene sulfonate)
Authors: Rosser Robin W. , Nemoto Norio , Schrag John L. , Ferry John D.
Published: April 2003

The storage and loss shear moduli G′ and G″ of dilute solutions of two samples of sodium poly(styrene sulfonate) with molecular weights (M) of 3.28 × 105 have been measured. The Birnboim–Schrag multiple‐lumped resonator technique was used in the frequency range 100–8000 Hz, and the intrinsic moduli were obtained by extrapolation to infinite dilution. Measurements were performed over the temperature range from 1.0 to 25.0°C in aqueous solvents containing from 0 to 60% by weight glycerol and from 0.001 to 0.005M added salt. The large intrinsic viscosities indicated high extension of the polymer, and the frequency dependences of G′ and G″ were matched well by hybrid relaxation spectra combining rodlike and coil‐like behavior. In a solvent containing 0.001M sodium ion and no glycerol, the end‐over‐end rotational relaxation times for the two molecular weights corresponded to proportionality to the 1.7 power of M. With increasing molecular weight, ionic strength, and/or glycerol concentration, the polyelectrolyte appeared to become less extended, and its behavior more nearly coil‐like.
Small‐angle x‐ray scattering by nylon 6
Authors: Matyi R. J. , Crist B.
Published: April 2003

Small‐angle x‐ray scattering (SAXS) of isotropic or uniaxially oriented nylon 6 was investigated as a function of thermal and mechanical history. In addition to the peak position and linewidth of the SAXS maximum, the integrated SAXS intensity was measured. It was found that the radial intensity distributions of isotropic or arced patterns are controlled to some extent by the small width of the semicrystalline macrolattice, rendering the conventional long period and line shape analysis inapplicable to these patterns. A two‐dimensional analysis is possible with well‐oriented fibers; the major structural changes which are seen in fibers after annealing above 190°C are associated with melting and recrystallization. Extensive cold drawing and subsequent annealing cause rather modest (ca. ∼30%) changes in the integrated SAXS intensity. These effects are consistent with the generation of homogeneous interfibrillar regions during the latter stages of plastic deformation. On annealing a quenched film on nylon 6, the transformation of the crystals from a pseudohexagonal to a monoclinic habit occurs above 170°C.
Four‐center photopolymerization. A heterogeneous topochemical solid‐state reaction
Authors: Meyer Wolfgang , Lieser Günter , Wegner Gerhard
Published: April 2003

The four‐center solid‐state photopolymerization of distyrylpyrazine (DSP) and of 2,6‐naphthalene bis(acrylic acid‐2,4‐dichloro phenyl ester) (NBA–DCP) was investigated by x‐ray and microscopic techniques. In both cases the polymer grows as a separate product phase topotactically well arranged with respect to the monomer matrix. In the case of polymerization of DSP the space group of the monomer (Pbca) is not maintained but the polymer phase has space group P21ca. Nucleation and growth of the polymer phase was observed by light and electron microscopy. Nucleation occurs at defect sites. The polymer grows at different rates in different crystallographic directions which were identified by electron diffraction in the case of DSP. Polymerization thus occurs in the transition region between monomer crystal and product phase and not in the bulk of the crystal so that the four‐center‐type photopolymerization is best described as a heterogeneous solid‐state reaction.