bluuebunny/crossref_metadata_2025 huggingface dataset:
Concentrated solutions of polydisperse rodlike polymers in the isotropic and lyotropic liquid‐crystalline phases. I. The effects of molecular length distribution on phase behavior
Authors: Moscicki J. K. , Williams G.
Published: April 2003

The earlier calculations of Moscicki and Williams of the phase behavior of rodlike macromolecules in solution incorporating a Gaussian distribution of rod lengths have been extended to include, in addition to a “basic” Gaussian distribution, a small amount of high‐molecular‐weight species which are characterized by a δ‐function or “box‐function” distribution. It is shown that C*p, the concentration of polymer at which the biphasic material (isotropic plus anisotropic phase) first appears may be substantially lowered in comparison with that for the system comprising only the basic distribution. The volume fraction ΦA of anisotropic phase, the compositions of the two phases, and the distribution of species between the phases are calculated for a range of polymer concentration which spans the isotropic, biphasic, and anisotropic phase and, among several features obtained, it is shown that the high‐molecular‐weight species are essentially responsible for the initial formation of anisotropic phase in the biphasic system. The results of the calculations have important implications for the interpretation of published dielectric relaxation data for polyalkylisocyanates in solution at high concentration and for published shear‐flow viscosity data for polyalkylisocyanates and poly(p‐benzamide) in solution at high concentration and these are discussed in some detail.
Phase transitions and structural properties of a thermotropic polyester
Authors: Kyotani Mutsumasa , Kanetsuna Hisaaki
Published: April 2003

The phase transition behavior and the structural properties of a thermotropic polyester, poly‐(chloro‐1,4‐phenylene‐trans‐1,4‐cyclohexanedicarboxylate), were studied by differential scanning calorimetry, x‐ray diffraction, polarized‐light microscopy, and electron microscopy. The polyester shows two first‐order transitions in heating, i.e., a crystal‐crystal transition and a crystal‐liquid‐crystal transition at 190–220 and 300–330°C, respectively. The texture in the liquid‐crystalline phase is very similar to that of nematic low‐molecular‐weight materials. Oriented films of the polyester can be obtained from the liquid‐crystalline state. Many fibrils occur in a fractured lateral surface of the film. Bandlike structures 50–100 nm wide were observed in surfaces of both oriented and unoriented films. The direction of the polymer chain axis is almost perpendicular to that of band elongation. In the oriented film, the band structures are perpendicular to the direction of orientation.
Structure and side‐chain interactions in poly(δ‐N‐carbobenzoxy L‐ornithine)
Authors: Sasaki Shintaro , Ban Hiroshi , Uematsu Ichitaro
Published: April 2003

Two crystal modifications are found in α‐helical poly(δ‐N‐carbobenzoxy L‐ornithine). In films as cast, the two‐dimensional unit cell is pseudohexagonal and contains two chains. This form transforms irreversibly into a pseudotetragonal form at about 140°C. A second‐order transition associated with the onset of the side‐chain motion is observed at about 30°C for the bulk sample (by dilatometry) and for the crystalline phase (by x‐ray diffraction). The dielectric behavior of the side‐chain dispersion suggests that the side chains interact with one another. The temperature dependence of the infrared absorbance due to the NH stretching vibration reveals that about half the side chains are associated via hydrogen bonds at room temperature and become dissociated at higher temperature. The enthalpy and the entropy of the hydrogen bond formation is estimated to be ΔH = −5.0 ± 0.5 kcal mol−1 and ΔS = −15 ± 1 e.u. mol−1.
Reversible isopentane‐induced depression of carbon dioxide permeation through polycarbonate
Authors: Chern R. T. , Koros W. J. , Hopfenberg H. B. , Stannett V. T.
Published: April 2003

Permeability data are reported for carbon dioxide in Lexan polycarbonate at 35°C. Measurements were made for both pure carbon dioxide and for a mixed feed consisting of carbon dioxide with a 117.8‐torr (0.155‐atm) Partial pressure of isopentane. The effects of varying upstream CO2 driving pressure from 1 up to 20 atm were studied. The permeability to CO2 is reduced significantly in the presence of isopentane; however, the fractional depression of the CO2 permeability due to the isopentane at low driving pressures is much more significant than at high CO2 driving pressures. The well‐known pressure dependence of carbon dioxide permeabilities in glassy polymers, therefore, is largely diminished by introducing isopentane to the pure carbon dioxide feed. These observations are consistent with a model for transport in glassy polymers which explains the observed trends in terms of competition between the two penetrants for microvoid sorption sites existing in the non‐equilibrium glassy polymer. Exclusion of carbon dioxide from microvoid sorption sites by the more condensable isopentane preempts transport through the microvoid regions, resulting in the observed depression of the CO2 permeability.
Poly(vinylidene fluoride)‐γFe2O3 magnetic composites
Authors: Reich S. , Goldberg E. P.
Published: April 2003

Magnetic metal‐polymer composites have been prepared by thermolysis of a metal carbonyl Fe(CO5) in poly(vinylidene fluoride). These composites comprise ca. 100‐Å‐diam iron‐oxide, γFe2O3, ferrimagnetic particles dispersed in the polymeric matrix. Small‐angle x‐ray studies show that these particles have a radius of gyration in the range 63–315 Å. The composites were prepared with up to ca. 20 wt % iron and were crosslinked, as evidenced by insolubility. Electron diffraction indicating the formation of some FeF2 suggests metal‐fluorine interaction during formation of the composite.
Radiation chemistry of linear low‐density polyethylene. II. Kinetics of alkyl and allyl free‐radical decay reactions
Authors: Basheer Rafil , Dole Malcolm
Published: April 2003

Quenched and annealed samples of linear low‐density polyethylene (LLDPE) were γ irradiated in vacuo at 77 K; the kinetics of the alkyl free‐radical decay reactions were studied at room temperature, and of the allyl free‐radical reactions at 60, 70, and 80°C. The ESR signals saturate at a slightly higher microwave power in the LLDPE than in high‐density polyethylene (HDPE), and the alkyl radicals start decaying at a lower temperature in the LLDPE than in the HDPE. As in the HDPE the decay of the alkyl free radicals at room temperature in the LLDPE follows the kinetic equation for two simultaneous first‐order reactions with the fraction of the faster‐decaying component being slightly greater in the quenched than in the annealed samples. In the case of the allyl free radicals the decay at 60°C follows the equation based on one fraction of the radicals decaying according to second‐order kinetics in the presence of other nondecaying radicals. At higher temperatures the data are best understood in terms of a second‐order rate equation with a continuously variable time‐dependent rate constant as suggested by Hamill and Funabashi.
Oxidative destruction of polyolefins under stress. The action of ozone on polyethylene and polypropylene
Authors: Popov A. A. , Blinov N. N. , Krisyuk B. E. , Karpova S. G. , Privalova L. G. , Zaikov G. E.
Published: April 2003

Tensile stresses accelerate the rate of oxidation by ozone of films of polyolefins, high‐density and low‐density polyethylene, and isotactic polypropylene. Experiments have been performed on thin (up to 20 μm) uniaxially oriented films under constant stress σ, under conditions where the chemical kinetics rather than diffusion dominates. It is found that the oxidation rate is proportional to exp(γ′σ/RT) where γ′ is an empirical constant. The effects of unimolecular chain scission and the change of molecular polymer parameters under stress on this dependence are negligible. An analogy with the kinetics of oxidation of stressed cycloparaffins by ozone is noted. A mechanism is suggested to explain the accelerating effect of tensile deformations on chemical processes involving rehybridization of carbon atoms in the main chain from the sp3 to the sp2 state. An ESR study with a stable nitroxyl radical probe revealed a change in the segmental mobility of polymer chains in the course of loading.
The onset of three‐phase separation in ternary polymer solutions
Authors: Fujita H. , Einaga Y.
Published: April 2003

A theoretical study is made of three‐phase separation in a ternary solution consisting of a pure solvent and two homologous monodisperse polymers with relative chain lengths P1 and P2. The Flory—Huggins interaction parameter X is assumed to depend linearly on the volume fraction ϕ of the polymer mixture: χ = χ0(T) + k(T)ϕ. For a given P1 the ratio of P2 to P1 for the onset of three‐phase separation increases with an increase in k, first gradually and then sharply. Loci of critical points for this condition on the χ0 vs. ϕ diagram are determined for a series of fixed values of P1 and their significance is discussed.
Rheological studies of moderately concentrated polystyrene solutions. I. A new method for the extrapolation of the zero‐shear viscosity
Authors: Ballauff M. , Krämer H. , Wolf B. A.
Published: April 2003

Measurements of the viscosity coefficient η of solutions of polystyrene (Mw = 6.0 × 105 and 1.77 × 106) in trans‐decalin (TD, θ solvent) and toluene (TL, good solvent) as function of shear rate (11−104 s−1), concentration (4.24−11.21 wt %), and temperature (10–50°C) are reported. As a new theoretically grounded method for the determination of the zero‐shear viscosity η0 it is proposed to plot η as a function of $\left({\eta \dot \gamma} \right)^3$. The intercepts of the straight lines obtained by this procedure give η0 in good agreement with directly measured values.
Existence of a distribution of hole‐trap activation energies in FEP‐Teflon
Authors: Hagekyriakou J. , Fleming R. J.
Published: April 2003

When FEP‐Teflon samples are electron irradiated at room temperature in open circuit and stored in that state for varying times following the end of irradiation, the temperature of the first current peak of the short‐circuit TSC plot increases with increasing storage time. A new model is presented to explain this phenomenon, its main features being (i) a quasicontinuous distribution of hole‐trap activation energies, the “center of mass” of the trapped hole population moving toward the deeper end of the distribution during the storage time, and (ii) an electron/hole recombination coefficient much smaller than that implied in an earlier model. It is shown that the assumption of a single dominant type of hole trap implies an unrealistically large frequency factor.
Nonlinear viscoelasticity and the Cox–Merz relations for polymeric fluids
Authors: Booij H. C. , Leblans P. , Palmen J. , Tiemersma‐Thoone G.
Published: April 2003

This investigation concerns the important class of fluids whose rheological properties are described by a quasilinear viscoelastic constitutive equation of the Boltzmann superposition type. The first Cox–Merz relation is closely approximated by such a fluid if its nonlinearity in shear can be described by the strain measure $ S_{12} (\gamma) = \int_0^\gamma {J_0} (\upsilon)dv $, irrespective of the distribution of its relaxation times and, hence, its linear viscoelastic properties. Here γ equals the shear strain and J0 the zeroth‐order Bessel function. The second Cox–Merz relation is met by materials with a different nonlinearity, namely S12(γ) = Si(γ), where Si is the sine integral. Experimental data on melts of a polystyrene and a low‐density polyethylene sample were utilized to demonstrate that both Cox–Merz relations cannot hold simultaneously.
Rheo‐optical studies on the deformation mechanism of semicrystalline polymers. XIV. Alpha and beta mechanical dispersions of spherulitic high‐density polyethylene and the dynamic orientation distribution function of crystallites
Authors: Fujita Ken‐Ichi , Niwa Hideyuki , Nomura Shunji , Kawai Hiromichi
Published: April 2003

The dynamic tensile deformation mechanism of spherulitic high‐density polyethylene was investigated by dynamic x‐ray diffraction at various temperatures and frequencies in order to assign the α and β mechanical dispersions explicity. The uniaxial orientation distribution function q(ζj,0) of the jth crystal plane and its dynamic response Δq′j(ζj,0) in phase with dynamic strain were observed for the (110), (200), (210) and (020) crystal planes. Then the orientation distribution function w(ζ,0,η) of crystallites (crystal grains) and its dynamic response Δw′(ζ,0,η), also in phase with the dynamic strain, were determined by a mathematical transformation procedure proposed by Roe and Krigbaum on the basis of the Legendre addition theorem. The temperature and frequency dependences of w′(ζ,0,η) were analyzed in terms of the model parameters for dynamic spherulite deformation combining affine orientation of crystal lamellae with several types of preferential reorientation of the crystal grains within the orienting lamellae. The following assignments are made: (i) The α mechanical dispersion must be assigned to the dynamic orientation dispersion of crystal grains within the crystal lamellae, involving two types of preferential rotations of the grains about their own crystal b and a axes. The rotation about the b axis is associated with lamellar detwisting, mostly in the equatorial zone of uniaxially deformed spherulites; the rotation about the a axis is associated with intralamellar shearing, mostly in the polar zone of the spherulites. Thus both rotations are intralamellar grain‐boundary phenomena. (ii) The β mechanical dispersion must be assigned to the dynamic orientation dispersion of the crystal lamellae behaving as rigid bodies. It is not accompanied by reorientation of the crystal grains, but is associated with orientation dispersion of noncrystalline material between the lamellae. Thus it is an interlamellar grain‐boundary phenomena.
In‐plane orientation of polyimide
Authors: Russell T. P. , Gugger H. , Swalen J. D.
Published: April 2003

As a nondestructive method of evaluation, we have used integrated optics to investigate thin films (<8 μm) of polyamic acid and polyimide as a function of molecular weight, initial imidization temperature, method of imidization, and annealing treatment. Polyamic acid films were found to exhibit a large optical anisotropy, indicating preferential alignment of the long axis of the molecule in the plane of the film. Imidization increased the birefringence of the film by a factor of 2.5 and reduced the film thickness. The only parameter that was found to effect the anisotropy of the films was the method of imidization. Chemical imidization was found to increase the birefringence by a factor of 3, indicative of a higher degree of molecular orientation parallel to the film surface. This effect was not observed in thicker (>25‐μm) films using x‐ray diffraction where the orientation function was found to be independent of the method of imidization.
The incipient characteristic tearing energy for an elastomer crosslinked under strain
Authors: Rivlin R. S. , Thomas A. G.
Published: April 2003

In a previous paper a two‐network model for an elastomer in which crosslinks have been introduced in the strained state, similar to that proposed by Green and Tobolsky, was used to calculate the dependence of the incipient characteristic tearing energy on the number of chain segments in each of the two networks, the number of links in these chain segments, and the deformation at which the crosslinking takes place. The tearing energies were calculated for tearing on planes perpendicular to the principal directions of this deformation. Here the calculations are extended to cover tearing on a plane with arbitrary orientation.
Concentration effects and thermodynamic nonideality in gel chromatography
Authors: Bleha T. , Spychaj T. , Vondra R. , Berek D.
Published: April 2003

The dependence of the elution volume Ve on the concentration of injected polymer c in gel chromatography is presented for several systems including poly(styrene) and poly(methyl methacrylate) in a number of pure solvents with SiO2‐based gels. The linear dependence of Ve on c and Kav on c (where Kav is the distribution coefficient) is confirmed in the region of very low concentration. The slopes k of the straight lines increase with increasing relative molecular masses M of the polymer injected and with increasing thermodynamic nonideality of the system (as expressed by the second virial coefficient A2). The significance of the slope of the GPC calibration curve for meaningful comparison of the concentration effects in various chromatographic systems is pointed out. A recently found correlation between k and (A2M)γ is confirmed with a γ value of about 0.8. A possible theoretical explanation for the deviation of γ from unity is discussed. Finally, the influence of both the polymer concentration and the thermodynamic quality of the eluent on the resolution index of the chromatographic system is evaluated with the conclusion that thermodynamically poor solvents should be preferred for preparative GPC separations with very high loads.
Theoretical models for diffusion in glassy polymers
Authors: Cohen Donald S.
Published: April 2003

A model is derived which incorporates and unifies many of the diverse observations occurring in diffusion in glassy polymers. This unification is made possible by explicitly formulating the common property of a glassy polymer in all its various modes, namely the finite relaxation time due to its slow response to changing conditions. The application and use of the model in various situations is discussed.
Glass transition in poly(propylene glycol) networks
Authors: Andrady A. L. , Sefcik M. D.
Published: April 2003

Difficulty in controlling and determining the structural parameters of polymer networks has hindered experimental studies on the glass transition in crosslinked polymers. A series of wellcharacterized networks of poly(propylene glycol) having narrow network chain‐length distributions and average molecular weight between crosslinksMcin the range of 425–3000 has been prepared. The glass transition temperaturesTgof these networks were found to vary linearly withM, consistent with several theoretical treatments. Both the physical crosslinking and the incorporation of crosslinking agent into the system (a “copolymer” effect) are shown to be responsible for increase inTgupon crosslinking in this system.

Varying the network chain‐length distribution without changingMcdid not affect theTgof the system. The chemical nature of the crosslinking agent, however, does affect theTgof the network, particularly at high crosslink densities.
Morphology of conducting organic polymers: Polythiophene and poly(3‐methyl thiophene)
Authors: Tourillon G. , Garnier F.
Published: April 2003

Polythiophene and substituted polythiophene can be electrochemically generated as very adhesive thin films or as thick powdery deposits. The homogeneity of the thin films is very high, but it decreases when the film thickness is increased. Scanning electron microscopy shows that the nature of the dopant strongly influences the film morphology. Transmission electron microscopy reveals mainly a fibrillar structure, with a fibril diameter of 200 Å in the undoped state, and 800 Å in the doped conducting state.
Silicone networks with junctions of high functionality and the theory of rubber elasticity
Authors: Flory Paul J. , Erman Burak
Published: April 2003

Results of Krik, Bidstrup, Merrill, and Meyers on polydimethylsiloxane networks of high functionality ϕ yield values of the reduced force [f*] in the high‐extension limit that are directly proportional to (vs/V) (1 − 2/ϕ) where vs/V is the number of effective chains in volume V. The contention that trapped entanglements contribute significantly to the modulus is refuted by adherence of the results to this proportionality down to the lowest degrees of interlinking. Features of the relationship of stress to strain that appear to be in conflict with current theory are attributable to crowding of chains about the junctions of high functionality and of large linear dimension in the networks investigated by these authors.
Estimation of crystallization temperatures in quenched polyethylene
Authors: Keith H. D. , Loomis T. C.
Published: April 2003

A numerical method has been employed to calculate crystallization temperature as a function of position in slabs or films of polyethylene quenched to various temperatures. The method is iterative, and combines a recent theoretical fit to empirical data for rate of crystal growth as a function of temperature with a solution to the thermal diffusion equation which takes latent heat into account. Results apply strictly only to transcrystalline regions near external surfaces but also provide lower limits to crystallization temperatures throughout the interiors of samples where spherulites nucleate ahead of the general crystallization front. Emphasis is given to assessing the relative importance of various physical parameters in determining crystallization temperatures.
Properties of crystallized trans 1,4‐polyisoprene
Authors: Mukherji S. , Woodward A. E.
Published: April 2003

Stirrer crystallization of a trans‐1,4‐polyisoprene fraction(M̄n = 3 × 105) was carried out from n‐butyl acetate and from n‐heptane solutions (2% w/v). Fibrous crystals in the ß form were obtained at temperatures of 46‐48°C in the two solvents, respectively. At 36‐46°C from n‐butyl acetate and 25‐35°C from n‐heptane lamellar crystallization took place leading predominantly to the α form. Melting endotherms and densities for various samples were obtained. The maximum TENDO for α was 74°C and for ß 79°C and the maximum weight fraction crystallinity for ß was 0.78. The stability of performed α nuclei in n‐butyl acetate and n‐heptane using a fraction with M̄n = 2.5 × 105 was monitored as a function of temperature. The dissolution temperature of fibrous ß‐TPI with the maximum TENDO was measured in 13 liquids and the results analyzed in terms of the Flory‐Huggins parameter. The heats of fusion for the α and ß forms, obtained by extrapolation of heat of fusion versus change in specific volume, were found to be 8.0 and 10 kJ mol−1, respectively. The pressure coefficients of the melting temperature were calculated to be 38 and 43 K kbar−1 and the fold‐surface free energies recalculated to be 42 ± 1 and 53 ± 1 erg cm−2 for the α and ß forms, respectively. The number of monomer units per average noncrystalline chain traverse for the most crystalline fibrous ß‐TPI was estimated at 36.
PCILO conformational energy calculation of model poly(vinyl chloride) molecules
Authors: Alig Ingo , Lochmann Rainer , Wartewig Siegfried
Published: April 2003

The quantum‐chemical PCILO method is applied to models for poly(vinyl chloride) molecules. Calculations of conformational energies were carried out on 2,4‐dichloropentanes. The values and the positions of the energy minima are determined and compared with results of other authors.
Dependence of maximum recoverable deformation of linear flexible‐chain polymers on limiting extension of the chains
Authors: Dreval V. E. , Vinogradov G. V. , Radushkevich B. V.
Published: April 2003

Uniaxial stretching and orientation of some linear flexible‐chain polymers have been investigated. A functional relation has been found between the maximum recoverable deformation and the limiting extension of the macromolecules. These deformations are found to increase in direct proportion to the square root of the degree of polymerization and to decrease with increasing stiffness of the polymer chain.
An estimation of the number of tie molecules in semicrystalline polymers by means of neutron scattering
Authors: Fischer E. W. , Hahn K. , Kugler J. , Struth U. , Born R. , Stamm M.
Published: April 2003

A new method for the evalution of neutron scattering data from semicrystalline polymers is proposed for small and intermiediate q [q = (4π/λ)sinθ/2]. It is based on the assumption that, in general, a molecule cryustallizes in various lamellae. Within one lamella the crystalline stems connected by loop or folds from intramolecular “clusters,” which are connected by tie molecules. Without further assumptions the method yields in a straightforward manner the following quantities: (i) the average number of clusters per molecule, from which the number of tie molecules can be estimated; (ii) the radius of gyration  of the centers of the stems belonging to one cluster; and (iii) the radius of gyration  of the cluster centers with respect to the center of the molecule the method was successfully tested using experimental data obtained from poly(ethylene oxide), polyethylene, and isotactic polypropylene.
The structure of copolymer crystals formed from dilute solution and in bulk
Authors: Domszy R. C. , Alamo R. , Mathieu P. J. M. , Mandelkern L.
Published: April 2003

The thermodynamic and structural properties of a series of hydrogenated polybutadienes, crystalized in the bulk and from dilute solution, have been investigated. These polymers are ethyl‐branched ethylene copolymers with narrow molecular weight and composition distributions. Despite the fact that for both modes of crystallization these random‐sequence copolymers display a lamellar crystalline habit, all of the independent physical chemical measurements are quantitatively consistent in indicating a relatively thin crystallite with a large amorphous disordered overlayer. This is seen to be a very general phenomenon for copolymer crystallization. The core thicknesses, determined from Raman LAM and from small‐angle x‐ray scattering, are in good agreement. Quantitatively consistent values of the degree of crystallinity are obtained from the density, enthalpy of fusion, Raman internal modes, Raman LAM, and small‐angle x‐ray scattering. It is significant that independent thermodynamic and structural methods give the same result.
Electron crystallography of epitaxially grown paraffin
Authors: Moss Barbara , Dorset Douglas L. , Wittmann J. C. , Lotz B.
Published: April 2003

Three‐dimensional electron diffraction data from the epitaxially crystallized paraffin n‐C36H74 are investigated in a structure analysis and are found to give a reasonable image of the structure, in agreement with the earlier x‐ray determination. An inconsistency in the refined isotropic temperature factors from different zonal projections, however, indicates the necessity for a more accurate physical model for epitaxially grown crystals which will account for a large spread of diffraction peaks along reciprocal lattice lines parallel to the projection axis.
Crystallinity and thermal properties of polyamides containing cis‐ and trans‐1,3‐cyclohexane rings
Authors: Inoue Kazuo , Hoshino Sadao
Published: April 2003

The cyclohexane ring‐containing polyamide 1,3‐CBMA‐6 was synthesized from 1,3‐cyclohexane‐bismethylamine (1,3‐CBMA) and adipic acid (6), and effects of cis/trans isomers of the ring on crystallinity and thermal properties were studied. Polymers with high cis and high trans contents, respectively, were made by polymerizing the 1,3‐CBMA‐6 salts of 98% cis and 93% trans derived from the salt of 75/25 (cis/trans) by fractional crystallization. A polymer with 97% cis content was highly crystalline, with a melting temperature of 253°C, while one with 93% trans contents was amorphous. In contrast to this, little difference was found in the glass transition temperature of 97 and 84°C. These results indicate that the isomers affect the conformation of the molecular chains, which determines the crystallinity and melting temperature, but they do not much affect the mobility of the chains as manifested by the glass transition.
Heterogeneous nucleation of poly(ethylene terephthalate)
Authors: Garcia Dana
Published: April 2003

The effect of various metal salts as nucleating additives for poly(ethylene terephthalate) (PET) has been investigated. In the case of sodium benzoate and probably for all other effective nucleating additives, the nucleation process can be divided into a “heterogeneous particle nucleation” performed by the unreacted salt and a “homogeneous nucleation” due to the polymer–sodium (metal) salt formed during the extrusion. This polymer–sodium (metal) salt is the major nucleating agent in these systems. We have also shown the fundamental difference between the concept of a nucleating additive and that of a nucleating agent.
Anomalous viscosity behavior of some poly(methyl methacrylate)s prepared by anionic polymerization
Authors: Corner T. , Peaker F. W.
Published: April 2003

A series of poly(methyl methacrylate)s with molecular weights in the range 3.0 × 104–1.03 × 106 have been prepared by anionic polymerization and their limiting viscosity numbers determined in a variety of solvents. It was found that whereas the higher‐molecular‐weight polymers behaved normally, the lower‐molecular‐weight polymers showed anomalous behavior. First, the limiting viscosity numbers of the lower‐molecular‐weight polymers were much higher than expected, and, second, their number‐average molecular weights as measured by gel permeation chromatography were considerably smaller than those determined by membrane osmometry.
Phase separation phenomena in solutions of poly(2,6‐dimethyl‐1,4‐phenylene oxide). IV. Thermodynamic parameters for solutions in a series of homologous solvents: Toluene to hexylbenzene
Authors: Koenhen D. M. , Bakker A. , Broens L. , Van den Berg J. W. A. , Smolders C. A.
Published: April 2003

Melting‐point curves for solutions of poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) in a series of homologous solvents (toluene to n‐hexylbenzene) have been obtained from visual and differential scanning calorimetry measurements. The measured melting points were used to calculate thermodynamic interaction parameters. It was found that consistent values were obtained with the Flory–Hoffman melting‐point depression equation, if the assumption was made that solvent molecules are incorporated in the crystal lattice. To this end, an adapted dependence of the enthalpy of melting per polymer unit on the cocrystallizing solvent was used. The values of the thermodynamic interaction parameters in the series of solvents and their dependence on polymer weight fraction are explained qualitatively with simplified versions of equation‐of‐state theory and solubility parameter theory.
Comments on “some evidence against the existence of the liquid‐liquid transition. IV. The temperature dependence of shear viscosity”
Authors: Boyer Raymond F.
Published: April 2003

A formal definition of TLL as a function of M̄n for polystyrene was prepared with literature TLL values from torsional braid analysis (TBA), differential scanning calorimetry (DSC), and zero‐shear melt viscosity η0. Data from six authors using anionically prepared PS and blends thereof were involved. The resultant linear least‐squares regression line, TLL(°C) = 148.5 − 11.487 × 104M̄ [standard error in TLL (calculated) 4.056 K, correlation coefficient R2 = 0.9534] is considered valid from M̄n = 2000 to the entanglement molecular weight Mc = 35,000. The “best” TLL values reported by Orbon and Plazek from double Arrhenius plots are well below this line for M̄v = 47,000, 16,400, 3400, and above it for M̄v = 1100. These best TLL values are artifacts arising from no or insufficient data points above or below TLL and/or too many data points near Tg. The associated high enthalpies of activation which they report confirm this diagnosis. The fact that these artificial TLL values tend to disappear when checked by the three‐parameter Vogel equation, logη = logA + B exp[(T − T∞)−1], has no relevance to the controversy concerning the existence and meaning of TLL. The claim by Orbon and Plazek that TLL values obtained by TBA, DSC, and melt viscosity are all artifacts of the individual methods by which they were obtained is inconsistent with the excellent master plot which they generate. Alternative plotting devices which reveal TLL > Tg from η0 vs. T−1 data, as developed by van Krevelen and Hoftyzer and by Utracki and Simha (not previously considered by either party), are reviewed. A statistical examination of the nature of the Vogel–Fulcher–Tammann–Hesse equation, based on synthetic data, is presented. Evidence for TLL in atactic polypropylene is offered based on published data by Plazek and Plazek. TLL is considered to possess both relaxational and quasiequilibrium attributes, just as Tg does.
Thermoplastic elastomers: Structural and morphological aspects of ether–esteramide copolymers
Authors: Cernia Enrico , D'ilario Lucio
Published: April 2003

Polyesteramide 6NT6–polytetramethylene ether glycol (PTMEG) copolymers, precipitated from dilute solution, have been studied by small‐angle x‐ray scattering (SAXS) and wide‐angle x‐ray scattering (WAXS) with variation of the PTMEG content. A comparison of the structural characteristics of these materials has been made with those of the 6NT6 homopolymer. Chain folding is assumed as the crystallization mechanism for the low‐PTMEG‐content copolymers, with possible inclusion of polyether segments within the 6NT6 crystal lattice. WAXS data support the view of a weakening of the 6NT6 crystalline packing in the equatorial planes as the reason for broadening of the diffraction peaks, for changes in their relative intensities, and for the increase in the equatorial interplanar distances in the high‐PTMEG‐content samples. The annealing behavior has also been investigated.
Thermal behavior of the poly(2‐methoxy)‐Cyanurate of 1,1′‐bis(4‐hydroxy phenyl)‐Cyclohexane
Authors: Parsania P. H. , Patel K. C. , Patel R. D.
Published: April 2003

Thermal behavior of unfractionated poly(2‐methoxy)‐Cyanurate, PMCBC‐ film has been reported. The degradation of the polymer involved two steps. The glass transition temperature, Tg, from DSC and DMA studies is ∼ 200°C. TMA study shows that the glass‐rubber transition region is in the range of 157 to 199°C. The thermal stability of PMCBC has been found to be superior to commercially available polymers.
Drawing of poly(p‐phenylene sulfide) by solid‐state coextrusion
Authors: Ito Masayoshi , Porter Roger S.
Published: April 2003

The effects of drawing temperature on the physical and mechanical properties of poly(p‐phenylene sulfide) have been studied. A melt‐quenched film was drawn by solid‐state coextrusion both below (75°C) and above (95 and 110°C) the glass transition temperature Tg (85°C) of PPS. The maximum extrusion draw ratio (EDRmax) increased from 3.4 to 5.6 with increasing extrusion temperature Te from 75 to 110°C. It was found that extrusion drawing just above the Tg of PPS (95°C) produced more stress‐induced crystals. A high efficiency of draw in the amorphous region was achieved by extrusion at Te‐75°C. The tensile modulus at EDRmax decreased from 5.1 to 3.5 GPa with increasing Te from 75 to 110°C. The low efficiency of draw for the samples extruded at 110°C is explained in terms of disentanglement and chain slippage during drawing due to a less effective network.
Studies of solution dynamics of poly(N‐vinyl pyrrolidone) and its iodine adduct
Authors: Cheng H. N. , Smith T. E. , Vitus D. M.
Published: April 2003

Carbon‐13 NMR spin‐lattice relaxation timesT1of poly(N‐vinyl pyrrolidone) (PVP) and PVP‐iodine have been studied in several solvents and at different temperatures. Three kinds of motion can be identified from theT1data: segmental motion, ring rotation, and ring puckering. The effective correlation time for segmental motion is calculated to be 1 × 10−9s, in good agreement with published proton NMR data. Another solvent, 1,1,2,2‐tetrachloroethane, behaves like D2O, the segmental correlation time being 3 × 10−9s. In benzene, however, the linewidths are very broad and tend to narrow with increasing temperature, but theT1s are not very different from those of PVP in D2O. The results suggest association of pyrrolidone rings in benzene that reduces chain dimensions and also restricts chain mobility. As for PVP‐iodine in water, again broad resonances are observed which sharpen considerably at higher temperatures. The result agrees with previous suggestions of specific interactions between the pyrrolidone group and iodine.
Low‐frequency Raman‐active modes and temperature dependences in oligo‐oxyethylene
Authors: Viras K. , King T. A. , Booth C.
Published: April 2003

Raman spectra have been recorded for monodisperse and polydisperse samples of oligooxyethylene at several temperatures in the range 310–77 K. Four scattering peaks are found with frequency dependent on temperature. One at 92–80 cm−1 is unaffected by changes in chain length and is assigned to a lattice mode. The others are chain‐length dependent and are assigned either to the longitudinal acoustical modes (LAM‐1 and LAM‐3)or, less certainly, to a transverse acoustical mode.
Crystallization of bisphenol‐A polycarbonate induced by organic salts: Chemical modification of the polymer. III. Reaction mechanism
Authors: Bailly Ch. , Daumerie M. , Legras R. , Mercier J. P.
Published: April 2003

In the presence of a sodium arylcarboxylate or arylphenoxide, bisphenol‐A polycarbonate (PC) undergoes complex chemical modifications at high temperatures. The reaction mechanism is similar to the one previously established for model systems. Initially, the salt reacts with the carbonate groups of the polymer. This lowers the number‐average molecular weight and produces ionic chain ends of the phenoxide type. A fast transesterification reaction is then induced by a continuous exchange between the phenoxide and the carbonate groups, affecting the molecular distribution until an equilibrium is attained. In the presence of CO2, the phenoxide‐terminated PC undergoes further chemical modifications (formation of phenyl salicylate and phenyl phenoxybenzoate groups) leading to progressive crosslinking of the polymer.
Study of molecular mobility in ultraoriented polypropylene by the spin‐probe technique
Authors: Choy C. L. , Leung W. P. , Ma T. L.
Published: April 2003

The rotational mobility of nitroxide radicals in polypropylene samples with draw ratios varying from 1 to 18 has been studied between 30 and 110°C by the ESR technique. The drop in the rotational frequency with increasing orientation correlates very well with the behavior of various other measures of molecular mobility such as organic vapor sorption, proton spin–spin relaxation times from NMR, and dynamic mechanical loss factor. This implies that each of these parameters is a good indicator of the amount of free volume in the amorphous regions. Annealing at high temperature relaxes the amorphous chain segments, thereby increasing the spin‐probe rotational frequency in the drawn samples to values even higher than that in the quenched isotropic material.
Correction of the mark–houwink–sakurada equation in the low‐molecular‐weight range
Authors: Dondos A. , Skordilis V.
Published: April 2003

A relation is proposed which gives the error in determination of molecular weights of polymer samples using the extrapolation of the Mark–Houwink–Sakurada equation into the low‐molecular‐weight region. The error is directly related to the exponent α of the Mark–Houwink–Sakurada equation and the relation is the same for a number of polymer + solvent systems.
Dilute‐solution properties of trans‐1,4‐polyisoprene
Authors: Chaturvedi P. N. , Patel C. K.
Published: April 2003

Trans‐1,4‐polyisoprene was fractionated by both fractional precipitation and preparative gel permeation chromatography to obtain possibly sharp fractions of narrow molecular weight distribution. Selected fractions were characterized by light scattering, viscosity, and gel permeation chromatography. Necessary corrections for molecular heterogeneity were applied. Some of the characteristic relations between [η] and Mw are [η] = 1.81 × 10−4 M in benzene at 30°C, [η] = 1.38 × 10−4 M in n‐hexane at 30°C, which are found to be in good agreement with literature data when corrected for molecular heterogeneity.
Craze fibril structure and coalescence by low‐angle electron diffraction
Authors: Yang Arnold C.‐M. , Kramer Edward J.
Published: April 2003

Brown has shown that low‐angle electron diffraction (LAED) may be used to determine fibril diameters D and spacings D0 of crazes in thin polymer films. He found, however, that the D and D0 determined for air crazes in polystyrene (PS) thin films were larger by about a factor of 3 than those in PS bulk crazes determined by using small‐angle x‐ray scattering (SAXS). We have repeated Brown's LAED experiments and find that the discrepancy may be caused by an aging effect. Our fresh crazes have D and D0 values from LAED that are comparable to those of bulk PS crazes determined by SAXS. As the craze ages, however, fibrils retract and coalesce in wide regions of the craze, leading eventually to an observable “skin.” Aged crazes thus have much larger D and D0 values than do fresh crazes. The large molecular mobility of the PS molecules in the fibrils necessary for this aging to occur at room temperature has important implications for fibril failure.
X‐ray scattering from the long spacing of completely crystalline oligoethylene glycol di‐n‐alkyl ethers
Authors: Swales Timothy G. E. , Domszy Roman C. , Beddoes Roy L. , Price Colin , Booth Colin
Published: April 2003

Completely crystalline samples of oligoethylene glycol di‐n‐alkyl ethers, H(CH2)nO‐(CH2CH2O)m(CH2)nH, where m is 9 or 15 and n is in the range 12‐18, were orientated in capillaries by slow crystallization in a temperature gradient. X‐ray scattering from the long spacings of the oriented samples, rotated continuously through 360°, was concentrated on the equator of a Debye–Scherrer photograph and many orders of reflection could be seen (e.g., up to order 30). The intensities of these reflections were analyzed by use of a model electron density distribution through the layer structure. Thus it was shown that the central oxyethylene block, in helical conformation, is oriented normal to the layer end plane, while the end alkyl bolcks, in planar zigzag conformation, are tilted relative to the layer end plane at an angle in the range 70°–64°.
Electrical properties of polyacetylene/polybutadiene blends
Authors: Sichel E. K. , Rubner M. F.
Published: April 2003

Microstructural Composites of polyacetylene/polybutadiene blends were prepared by polymerizing polyacetylene in a matrix of polybutadiene. The polyacetylene in the blends can be doped with iodine to produce electrically conducting composites. Thus a new material is formed which retains many of the electrical properties of doped polyacetylene but whose mechanical properties are different from those of either polyacetylene or polybutadiene.
Quantum yield for poly(methyl methacrylate) chain scission by 214–229 nm wavelength light
Authors: Shultz A. R. , Frank P. , Griffing B. F. , Young A. L.
Published: April 2003

The quantum yield for poly(methyl methacrylate)chain scission by ultraviolet light in the 214–229 nm wavelength region was found to be ϕd = 0.03 scissions per absorbed photon. Samples were 1.65‐μm films spun cast on silicon wafers and irradiated under flowing nitrogen by a cadmium vapor lamp. Gel permeation chromatography was used for molecular weight determination. Heating (postbaking) the irradiated films at 150°C for one hour under reduced‐pressure flowing nitrogen increased the observed scissions per absorbed photon to 0.04. Glass transition temperatures by DSC are well‐represented by Tg (K) = 393.3 − 2.0 × 105/Mn for the postbaked samples (139,000 > Mn > 6500).
Polyethylene fiber formation in tubular flow. II. Discussion of precursor formation and nucleation time analysis
Authors: Mchugh A. J. , Rietveld J.
Published: April 2003

This is a continuation of the preceeding paper, Part I, and presents a discussion of the nature of the precursor structure formation process observed in the flow‐induced crystallization experiments described in I. A discussion of stress‐induced crystallization theory as applied to these experiments is also given and a first‐order analysis of crystal nucleation rates is presented. Conclusions regarding the nature of flow‐induced crystallization and our current ability to quantitatively model the overall process are also presented.
Rheo‐optical fourier‐transform infrared spectroscopy of polymers. 9. Stretching‐induced II(α)‐I(β) crystal phase transformation in poly(vinylidene fluoride)
Authors: Siesler H. W.
Published: April 2003

Simultaneous Fourier‐transform infrared (FTIR) spectroscopic and stress‐strain measurements have been used to study the II(α)‐I(β) crystal phase transformation in poly(vinylidene fluoride) under tensile stress at variable temperature. From the experimental data it can be derived that in the investigated temperature interval from 348 to 423 K the drawing process is inhomogeneous and occurs via formation of a neck. The II(α)‐I(β) phase transformation is restricted to temperatures below 423 K and its onset is generally related to the formation of the neck.
Translational diffusion of polystyrene in cyclohexane at infinite dilution from 283 to 348 K
Authors: Barooah A. , Chen S. H.
Published: April 2003

The translational diffusion coefficients are reported for polystyrenes with molecular weights 2000, 4000, and 9000 in cyclohexane at infinite dilution from 283.2 to 348.2 K. The results suggest that the hydrodynamic radii stay constant to within ±3% and that the real chain for molecular weight 9000 at 308.2 K is well represented by a Gaussian or Monte Carlo model involving the idea of statistical steps. Furthermore, the success of Hildebrand's free‐volume empiricism has led to a correlation between Dμ0/T and M which represents the observed diffusivities to within ±2%.
Evaluation of theories for diffusion in polymer–solvent systems
Authors: Vrentas J. S. , Duda J. L. , Hou A.‐C.
Published: April 2003

A method is proposed for examining differences in the predictive capabilities of three versions of the free‐volume theory of polymer—solvent diffusion using only a small amount of diffusivity data. The utility of the method is illustrated using a limited diffusivity data set for the methanol‐poly(vinyl acetate) system.
An x‐ray diffraction study of nonlinear polyethylene. II. Small‐angle scattering observations near the melting point
Authors: Vonk C. G. , Koga Y.
Published: April 2003

A method is presented for obtaining from the zeroth‐order peak in small‐angle x‐ray scattering (SAXS) patterns the weight average of the thickness C of crystalline lamellae in polymers close to the melting point. The method fails if a first‐order peak can be discerned to be superimposed on the zeroth‐order peak. The method was applied, together with the one described in Part I of this series for obtaining the number average of C, to three polyethylene samples of different side‐group content which were heated to temperatures close to the melting point. While heating always causes an increasing number of lamellae to melt, a linear sample also shows pronounced thickening of the remaining lamellae. This effect, however, decreases with increasing side‐group content, and is virtually absent in a vinyl acetate copolymer containing 53 side groups per 1000 C atoms. A qualitative explanation for the role of the side groups in limiting the crystal thickening processes is put forward. By comparing results obtained after isothermal annealing and during isothermal crystallization from the melt it is concluded that at temperatures close to the melting point the polymers approach a final state which no longer depends on the thermal history of the sample.