bluuebunny/crossref_metadata_2025 huggingface dataset:
Interfacial polycondensation. XII. Variables affecting stirred polycondensation reactions
Authors: Morgan Paul W. , Kwolek Stephanie L.
Published: April 2003

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

Much recent work has been carried out on the tear behavior of elastomers, both filled and unfilled, especially by workers at the Natural Rubber Producer's Research Association. By use of a criterion for tearing involving the concept of the tearing energy, the effects of variables such as test temperature, test rate, specimen geometry, and chemical nature of the elastomer have been investigated. The one variable which has not yet been studied is the specific effect of changes in the degree of crosslinking on tear behavior. By use of data published in the literature on the smooth tear behavior of unfilled SBR vulcanizates, it is shown that these data can all be superposed onto a common response curve when the proper normalizations are applied.
Laser‐Raman study of the longitudinal acoustic mode in polyethylene
Authors: Olf H. G. , Peterlin A. , Peticolas W. L.
Published: April 2003

A Raman band of low frequency, arising from an accordionlike vibration of all‐trans \documentclass{article}\pagestyle{empty}\begin{document}$ \rlap{‐‐} ({\rm CH}_2 \rlap{‐‐})_n $\end{document} segments and previously observed in normal paraffins and in polyethylene single crystals, has now also been found in bulk and in cold‐drawn polyethylene, both linear and branched. The accordionlike vibration, or longitudinal acoustic mode (LAM), in polyethylene is compared with the LAM in normal paraffins. Whereas the Raman bands corresponding to the third (LAM‐3) and higher modes are quite intense in a long‐chain paraffin such as n‐C94H190, they are so weak in polyethylene as to be unobservable with the apparatus used. This is attributed to the presence of the chain fold in polyethylene. Of the two extreme structural models of the fold here discussed, namely the models of “tight folds” and of “loose loops,” only the latter seems capable of accounting for the weakness of LAM‐3 and higher modes in polyethylene. A quantity called “nominal Raman length” is defined as the length of that all‐trans n‐paraffin that would have the same LAM‐1 frequency as the polyethylene sample under consideration. The nominal Raman length is always greater than the average long spacing, deduced from discrete x‐ray scattering at small angles after applying a Lorentz correction, and, after allowing for chain tilt, is found equal to the segment length between folds. This can be accounted for by both of the models mentioned. As a test of the theory of surface melting the frequency of the accordion vibration of annealed polyethylene single crystals was measured as a function of temperature up to the melting point; no frequency change with temperature was observable. On the basis of the naive idea that there is complete decoupling of the vibrations in the all‐trans chain segment from the disordered (molten) surface layer, one would predict that upon surface melting and the concomitant shortening of the all‐trans segment, the LAM‐1 frequency should increase. A more careful analysis, taking into account the existence of coupling of the LAM to the surface layer, shows that the outcome of this experiment does not necessarily invalidate the idea of surface melting. Bulk polyethylene samples exposed to 60Co γ‐radiation for doses up to 100 Mrad show a slight shift of the Raman band to lower frequencies, whereas no such shift was observed upon absorption of a swelling agent. A search, without success, was made for a longitudinal acoustic mode in polypropylene, poly(vinylidene fluoride), nylon 66, and polyoxymethylene.
Atomic mechanism of fracture of solid polymers
Authors: Zhurkov S. N. , Korsukov V. E.
Published: April 2003

Macromolecular chain scission under mechanical stress has been studied by infrared spectroscopy. The dependence of accumulation of chemical bond scissions on temperature T and uniaxial tensile stress σ has been investigated. The rate constant K for bond dissociation under mechanical stress has been found to obey the modified Arrhenius equation: K = K0 exp{ − (EA − ασ)/RA}. The quantitative connection between the rate constant for bond dissociation and mechanical lifetime τ has been established. Analysis of the experimental data indicates that the strength and mechanical lifetime of polymers is determined by the kinetics of mechanochemical scission of the main chains of polymer molecules.
Excluded‐volume effect for various chain models. I. Application to optical anisotropy and end‐to‐end distance of linear polymers
Authors: Lemaire Bernard , Fourche Georges , Sanchez Edouard
Published: April 2003

A study of the effect of excluded volume on the mean‐square optical anisotropy 〈γ2〉 and the mean‐square end‐to‐end distance 〈R2〉 has been carried out for polymer chains of up to 2000 bonds. The calculations have been made for models assuming (a) equiprobability of internal rotations and (b) interdependence of short‐range intramolecular interactions. All the results indicate that 〈γ2〉 is practically insensitive to the excluded‐volume effect. Concomitantly the behavior of 〈R2〉 has been analyzed.
Small‐angle light scattering from hedrites, ovoids, and spiral ovoids. I. Theoretical considerations
Authors: Gałȩski A. , Kryszewski M.
Published: April 2003

Taking into consideration results of our microscopy studies and data given in the literature on the structure of hedrites, ovoids, and spiral ovoids, we have developed optical models for these morphological entities. These models are applied to calculations of small‐angle scattered light intensity distributions for these structural elements. Analytic formulae computed for the Vv and Hv scattering patterns contain terms dependent only on azimuthal angle μ and vertical angle θ. For hedrites and ovoids, equations are derived relating the characteristic points of scattered light intensity patterns to structural parameters. The corresponding diagrams of light intensity distributions are given.
Gas sorption in polymer membranes containing adsorptive fillers
Authors: Kemp D. R. , Paul D. R.
Published: April 2003

The equilibrium and kinetics of gas sorption by a silicone rubber filled with highly adsorptive molecular sieves was studied. Sorption in this system is by two mechanisms: gas is simply dissolved in the polymer matrix according to Henry's law, while it is adsorbed by the dispersed sieve phase in accordance with a Langmuir's isotherm. The latter effectively immobilizes the gas molecules preventing their further diffusion. All equilibrium parameters were determined experimentally. Immobilization greatly affects sorption kinetics and renders conventional analyses invalid. A theory to account for this process was adapted from a previous analysis by Vieth and Sladek which assumes that the kinetics of adsorption is very fast compared to diffusion. For this situation the kinetics always assume a Fickean form. The experimental data agreed very well with the predictions of this theory in a comparison where all parameters were defined by independent experiments. It was found that a single effective diffusion coefficient describes sorption kinetics, steady‐state permeation, and time‐lag results once the effects of immobilization are properly accounted for.
Rheology of poly(vinyl chloride) melts. II. Shear rate‐dependent properties
Authors: Utracki L. A.
Published: April 2003

Four samples containing 40, 60, 80, and 97 wt‐% of poly(vinyl chloride), the rest being plasticizer and stabilizer, were tested by using the Weissenberg Rheogoniometer in the steady‐shearing mode at temperatures between 155 and 235°C and rates of shear \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma = 0.01 - 400 $\end{document} sec−1. The viscosity η versus \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document} follows Graessley's theoretical dependence for infinitely entangled system. The primary normal‐stress difference coefficient ψ versus \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document} is well described by the same theoretical function, used with the square of its argument. The temperature dependence of η0 and ψ0 shows discontinuities at T = Tb. The numerical values of Tb can be calculated from the theory of the melting point depression due to diluent. The activation energy of viscous flow Eη below Tb is 5–9 times as large as above this temperature. The activation energy of normal stress is found to be Eψ ≈ 5Eη. The characteristic relaxation times τo, ψp, calculated from superposition of η versus \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document} and ψ versus \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \gamma $\end{document} data, respectively, onto Graessley's master curves, and τN, computed from zero shear parameters η0 and ψ0, differ in their sensitivity to the melting of microcrystalline regions. It is postulated that in the systems investigated, aggregates with long lifetimes are being formed, increasing the effective molecular weight and introducing changes in the effective polydispersity.
NMR spectrum of poly(vinyl chloride)
Authors: Hassan A. M.
Published: April 2003

The 100‐MHz proton NMR spectra of commercial and laboratory‐prepared poly(vinyl chloride) (PVC) have been measured in various solvents at high temperature (80–150°C). Tacticity in PVC was determined by the analysis of the β‐proton spectrum. The spectrum was calculated assuming that the PVC chain consists of tetrad sequences of monomer units and that their distribution in the chain is described by a simple Bernoulli‐sequence statistics with a Pm (the probability of isotactic placement) of 0.45 for commercial PVC polymerized at 50°C. Tacticity calibration curves based on measurements made for the polymer in pentachloroethane and β‐dichlorobenzene were established, and they provide a simple method for the measurement of tacticity in PVC directly from the observed spectra. Excluding samples prepared in butyraldehyde solution, the formation of syndiotactic structures in PVC (prepared by free‐radical polymerization) was found to be favored by lowering the polymerization temperature. This preference is due to an increase in the activation enthalpy of 510 cal/mole which is required for forming an isotactic placement in the chain during the propagation step.
A lattice theory of light scattering from disordered spherulites
Authors: Yoon Do Yeung , Stein Richard S.
Published: April 2003

A lattice theory of orientational disorder in two‐dimensional spherulites is developed in which the orientation direction of the optic axis in lattice cells is allowed statistically to deviate from its mean value in a manner correlated with the orientation in neighboring cells. The Hv light scattering patterns arising from such disordered spherulites deviate from the patterns for perfect spherulites in that there is excess intensity at both small and large scattering angles and the intensity at the maximum is lower. A comparison of the calculated scattering angular dependence with that which is experimentally measured permits assignment of values of correlation parameters. A consequence of this disorder is that the spherulite birefringence is reduced below that calculated on the basis of perfect crystalline orientation in agreement with experiment.
Solution properties of high molecular weight polystyrene
Authors: Fukuda Mitsutoshi , Fukutomi Makoto , Kato Yoshio , Hashimoto Tsutomu
Published: April 2003

A series of polystyrenes with weight‐average molecular weight M̄w up to 1.3 × 107 was prepared by anionic polymerization in tetrahydrofuran (THF). Each sample was characterized by gel‐permeation chromatography, light scattering, and viscometry. It was found that each sample had an almost symmetrical and very narrow molecular weight distribution (M̄w/M̄n < 1.07). The mean‐square unperturbed radius of gyration 〈S2〉0 was determined in trans‐decalin at 20.4°C as 〈S2〉0 = 7.86 × 10−18M̄w (cm2). The particle scattering factor was well represented by the Debye equation irrespective of solvent in the range of M̄w < 4 × 106, and only a small deviation was observed in benzene at higher molecular weights. The penetration function Ψ ≡ A2M2/4π3/2NA〈S〉23/2 was found to approach a relatively low asymptotic value of 0.21–0.23 at molecular weights above 2 × 106 in benzene at 30°C, where A2 is the second virial coefficient and NA is Avogrado's number. It was also found that the theta temperature in trans‐decalin was affected by the nature of polymer samples. A difference of about 3°C in the theta temperature was observed between two series of anionic polystyrenes, one prepared in THF and the other in benzene, but there was practically no difference in unperturbed chain dimension.
Electronic conduction and polarization in polyphthalocyanines
Authors: Norrell Charles J. , Pohl Herbert A. , Thomas Mani , Berlin K. Darrell
Published: April 2003

The polymeric hydrogen form of phthalocyanine is found to be more conductive than the metallic derivatives, in contrast to the behavior of the monomers. In addition, the polymers were found to be much more conductive than the corresponding monomers with the resistivity of the polymers ranging from 7 ohm‐cm to about 3 × 106 ohm‐cm. The polymers were found to have moderately high dielectric constants ranging from 16 to 1300 at room temperature, depending upon the applied pressure. Based on the dependences of the conductivity and permittivity upon the electric field strength, the average molecular length of the conductive paths within the polymer molecule has been estimated to be 100–1000 Å. In view of these estimated lengths, together with the exponential dependence of the permittivity and conductivity upon the pressure and temperature, the dispersion of the dielectric constants in the range of 10–100 KHz, and the chemical architecture of these ribbonlike polymers, the electronic behavior of these polymers is concluded to be consonant with the model of essentially one‐dimensional conduction within and along the chains by freed charges. Much as in a number of previously studied highly conjugated polymers, the present polyphthalocyanines are semiconducting and exhibit nomadic polarization, with dielectric constants ranging from 70 to 1300.
Properties of cellulose acetate in solution. I. Light scattering, osmometry, and viscometry on dilute solutions
Authors: Tanner D. W. , Berry G. C.
Published: April 2003

Light‐scattering, osmotic pressure, and viscometric studies on fractions of cellulose acetate (degree of substitution 2.45) in three solvents are described. The data yield the dependence of the mean‐square radius of gyration 〈s2〉, the second virial coefficient Γ2, and the intrinsic viscosity [η] on molecular weight M and temperature. The results are interpreted to show that excluded volume effects on 〈s2〉 are negligible, even though Γ2 is large and dΓ2/dT is positive. The large experimental value of d In [η]/d In M is interpreted in terms of partial draining effects. Data on 〈s2〉 and [η] for other cellulose esters in the literature are similarly interpreted. Significant aggregation found in solutions of cellulose acetate in many solvents is discussed.
Vibrational spectra of thiuram sulfides: Normal coordinate analysis of tetramethylthiuram mono‐, di‐, and tetrasulfides
Authors: Coleman M. M. , Koenig J. L. , Shelton J. R.
Published: April 2003

The normal coordinate analyses of tetramethylthiuram mono‐, di‐, and tetrasulfides have been carried out by utilizing vibrational energies obtained from infrared and Raman spectroscopic data reported here. The CS vibration is demonstrated to be highly coupled and to contribute to frequencies in the 850–1000 cm−1 region, but can be identified based on the strong Raman intensity. The results are useful in interpreting the spectra of these complex vulcanizing agents.
Molecular weight–mechanical property interrelationships. V. Poly(vinyl chloride) fracture surfaces: The effect of molecular weight and vapor environment
Authors: Martin John R. , Johnson Julian F.
Published: April 2003

The fracture and craze surfaces of four PVC fractions (M̄w = 51000 to 228000) and two bimodal blends were examined with a scanning electron microscope. The fraction with the lowest molecular weight gave brittle fractures when fatigued in nitrogen and ethanol vapor. Walls of crazed ductile matter formed at the surface of higher molecular weight samples. Thickness of this ductile material increased with molecular weight. There appeared to be a balance between craze propagation into the sample and brittle fracture due to dilitational and tensile stresses in the interior regions of the test films.
Excluded volume effect for various chain models. II. Application to optical anisotropy and end‐to‐end distance of branched polymers
Authors: Lemaire Bernard , Fourche Georges
Published: April 2003

Monte Carlo simulation has been used to investigate the excluded volume problem for branched polymers. The mean‐square optical anisotropy and mean‐square end‐to‐end distance were examined for two models including short‐range intramolecular interactions. Molecules of regular‐comb and random‐comb type were studied. The various effects found are discussed.
An etching technique to reveal the supermolecular structure of crystalline polymers
Authors: Bartosiewicz L. , Mencik Z.
Published: April 2003

Highly polished surfaces of nylon 6, nylon 66, polychlorotrifluoroethylene and polypropylene were etched by aromatic and chlorinated hydrocarbons at temperatures between 25 and 75°C to reveal surface morphology. Comparison with micrographs obtained with microtomed sections shows the absence of etching artifacts which are known to accompany the use of oxidizing etching agents.
Statistical mechanics of two‐dimensional wormlike chains
Authors: Fujii Motoharu , Shimada Jiro , Yamakawa Hiromi
Published: April 2003

The bivariate distribution function and the ring closure probability for a continuous wormlike chain derived by Gobush et al. and by Yamakawa and Stockmayer are translated into the two‐dimensional case. The results may be written in terms of Fourier series instead of spherical harmonics. Evaluation is carried out to terms of order t−3, where t is the ratio of the total contour length to the persistence length.
High‐speed gel‐permeation chromatography
Authors: Kato Yoshio , Kido Shiro , Yamamoto Manabu , Hashimoto Tsutomu
Published: April 2003

To establish optimum operating conditions for high‐speed gel‐permeation chromatography (GPC), the effects of column packing particle size, solvent flow rate, and column length on the separation efficiency have been investigated by using monodisperse polystyrene samples and polystyrene gel columns (TSK‐GEL column, Type‐H). Decreasing the particle size of the column packing reduces the time required to obtain a given resolution. Monodisperse polystyrene standards were measured under the optimum operating conditions established (gel particle size 5 μ, column length 2 ft, flow rate 2.5 ml/min). The molecular weight distribution of a polymer mixture was determined in less than 10 min with the same accuracy as by the conventional GPC. Such short analysis time enables one to use GPC for in‐plant quality control.
Stress relaxation in carbon‐black‐filled styrene–butadiene rubber
Authors: Oono Ryo
Published: April 2003

The tensile stress relaxation of carbon‐black‐filled SBR was studied in the linear viscoelasticity region as a function of temperature and volume fraction of fillers. Time—temperature superposition was valid, and master relaxation curves were obtained. Carbon black increases the modulus of the compound, especially in the rubbery region, and the time range over which the glass‐rubber transition occurred. The shift factor is divided into three regions; an Arrhenius dependence in rubbery and glassy states, and Williams‐Landel‐Ferry (WLF) dependence in the transition region. The apparent activation energy in the rubbery state increases with the volume fraction of carbon black (or silica) and is unaffected by the structure of the filler. The increase in activation energy is caused by the attachment of rubber chains to the carbon surface. At 30% elongation, the activation energy for carbon‐black‐filled rubber has a value of 32 kcal/mole, independent of structure and concentration of the filler.
Form birefringence of crystalline polymers
Authors: Chang C. , Peiffer D. , Stein Richard S.
Published: April 2003

The theory of Franklin et al. is employed for the calculation of the maximum form birefringence of a polymer having lamellar morphology. The results confirm the experimental conclusion that for low‐density polyethylene, the form birefringence approaches 3% of the total birefringence. The theory also predicts the parabolic dependence of the form birefringence on the refractive index of the amorphous phase. It may be applied to estimate the dynamic form birefringence and leads to a value of the dynamic strain‐optical coefficient which is of the order of 2–15% of the total.
Studies of the amorphous region of polymers. I. Relationship between the change of structure and glass‐transition temperature in drawn poly(ethylene terephthalate)
Authors: Ito Eiko , Hatakeyama Tatsuko
Published: April 2003

The effect of drawing on the glass‐transition temperature of amorphous poly(ethylene terephthalate) has been studied. The Tg decreases to a minimum at a draw ratio of 1.5, then increases to a maximum at a draw ratio of about 2.0, and again decreases with increasing draw ratio. The relationship between the change of structure and Tg is discussed in terms of the configurational entropy and the rate of molecular motion in local‐mode relaxation. On the basis of configurational entropy, the decrease of Tg at the beginning of drawing depends on the increase of configurational entropy, while at draw ratios above 2.0 it depends on the increase of entropy associated with intermolecular interaction. From the point of view of molecular motion, it is concluded that the change of Tg is determined by local oscillations in the amorphous region.
Light scattering studies of narrow fractions of polyethylene
Authors: Go Santos , Mandelkern Leo , Prud'Homme Robert , Stein Richard
Published: April 2003

Small‐angle light scattering experiments were conducted on thin films of linear polyethylene fractions over a very wide range of molecular weights. Spherulitic structures were found in all samples with molecular weight 9 × 105 or less. A rodlike morphology predominates for molecular weights between 1 × 106 and 2 × 106. Still higher fractions yield a very disordered superstructure. These results can be correlated with previous studies of the overall crystallization rates and the resulting properties.
Dilute solution properties and phase separation of branched low‐density polyethylene
Authors: Nakano Seikou
Published: April 2003

Viscosity, light scattering, and precipitation temperature measurements on dilute solutions of high‐density and low‐density polyethylene fractions have been carried out and a theory by Flory for phase equilibrium of linear polymers has been extended to branched polymer. From the results, it is shown that the entropy parameter ψ, depends on branching; a method for the determination of long‐chain branching in polymer fractions is proposed combining precipitation temperature and molecular weight measurements. The method has been applied to the evaluation of long‐chain branching in low‐density polyethylene.
Dynamic mechanical properties of glass‐filled epoxy resin
Authors: Ebdon Michael P. , Delatycki O. , Williams John G.
Published: April 2003

Composite specimens were prepared using soda glass beads and a purified epoxy resin cured with 1,3‐propylene diamine. Some beads were treated with a silane coupling agent. The dynamic mechanical properties of these specimens were measured in the temperature range −190 to +180°C using a free‐oscillation torsion pendulum. The dynamic mechanical relaxation spectrum showed no feature that could be attributed to the formation of a new interfacial phase and the torsional moduli were unaffected by the use of the coupling agent. Increasing the glass content of the specimens decreased the damping and increased the modulus. An attempt was made to predict the composite modulus using the Kerner equation. When the specimens were immersed in boiling water, two effects were noted. First, water was absorbed in the epoxy resin matrix and changes in the dynamic spectrum were observed. Second, in samples filled with untreated glass debonding occurred and the presence of free water at the interface was indicated by the appearance of a new peak near 0°C.
Dynamic polarized infrared studies of stress relaxation and creep in polypropylene
Authors: Wool R. P. , Statton W. O.
Published: April 2003

A new technique was developed to study the molecular mechanics of highly oriented polypropylene during stress relaxation and creep. The polarized infrared spectrum was recorded while the polymer was under load. Stress relaxation effects were investigated during the two‐stage process of fast decay followed by a slower “dynamic equilibrium” decay by examining the stress‐sensitive 975‐cm−1 band and the orientation‐sensitive 899‐cm−1 band. In the fast decay region, the aligned chains became more highly overstressed and the nonaligned chains quickly relieved themselves of their initial overstress. These findings suggest an exchange of stress from nonaligned to aligned chain segments, without much orientation change. Also, a rupture of very highly overstressed aligned chains is though to occur. In the slow decay region, the aligned overstressed chains showed a relief of stress accompanied by some disorientation or helix distortion. Creep, however, appeared to occur via a process which involved all chains regardless of alignment. It was found that the number of highly stressed bonds increased with time at the expense of the intermediately stressed bonds. Very little change in overall orientation was noted, which probably explains the observed crazing and void formation.
Relationship between structure and transport in cellulose acetate desalination membranes
Authors: Sudduth R. D. , Rogers C. E.
Published: April 2003

Several experimental techniques, including measurements of salt rejection, water flux, birefringence, and membrane opaqueness, were used to characterize the structure and performance of typical cellulose acetate desalination membranes. The results indicate that optimum salt rejection and water flux characteristics are related to the presence of molecular orientation effectively perpendicular to the membrane surface. An alignment‐type flow mechanism involving water contained within the oriented structure is consistent with the observed structural and transport phenomena. The various membrane fabrication procedures apparently have significant effects on the development of molecular orientation in the thin surface layers of the membrane.