bluuebunny/crossref_metadata_2025 huggingface dataset:
Ellipsometric study of the adsorption of comb‐branched polystyrene onto a metal surface
Authors: Kawaguchi Masami , Takahashi Akira
Published: April 2003

The adsorption of well‐characterized comb‐branched polystyrene onto a chrome plate from cyclohexane solution at the θ temperature has been studied by ellipsometry. Both the adsorbance of the polymer and the extension of the adsorbed layer are compared with values for the linear polystyrene of the same molecular mass. The adsorbance is higher than that of the linear polystyrene, whereas the extension of the adsorbed layer is smaller, reflecting the higher segment density of the branched polymer. The extension tb of the branched polymer is given approximately tb = tlg, where tl is the extension of linear polystyrene of the same molecular mass and g is the ratio of the radii of gyration of the branched and linear polymers. The ratio of the adsorbances Ab/Al of branched and linear polymer is approximately equal to g. These results indicate that the comb‐branched polymer is adsorbed as a slightly distorted randam coil with extension and adsorbance governed primarily by the experimental gs factor.
Piled‐lamellae structure in polyethylene film and its deformation
Authors: Tagawa Takashi , Ogura Kazumichi
Published: April 2003

The fine structure of polyethylene film has been investigated by using a high‐resolution scanning electron microscope equipped with a field emission source. The original film surface of a‐axis‐oriented blown polyethylene film and the surface of a necked region formed by drawing the film in the machine direction were observed. High magnification electron micrographs indicate that the basic unit of internal texture of this film consists of piled‐lamellae units, each pile containing three to ten lamellar crystal sheets. The piled‐lamellae unit acts as one body and does not separate into single lamellae during deformation. Many tie fibrils are formed between adjacent piled‐lamellae units, when the film is drawn in the machine direction. Although little attention has been given to this mechanism, it is important in deformation. This fact seems to be reflected in different shapes of the stress‐strain curves of films drawn the machine direction and perpendicular to it.
Molecular theory of piezoelectricity of α‐helical polypeptide
Authors: Namiki Koji , Hayakawa Reinosuke , Wada Yasaku
Published: April 2003

A molecular theory of the piezoelectric constant of the α‐helical backbone of polypeptide is developed on the basis of fluctuation formalism. The piezoelectric constant, electric susceptibility, and elastic compliance of the α‐helix are calculated through the method of molecular lattice dynamics by use of normal‐coordinate analysis. Displacements of each atom due to the external stress exerted upon the backbone are also calculated. The piezoelectricity of the α‐helix is concluded to arise mainly from rotation of the CONH bond. The value of the piezoelectric constant of poly(γ‐benzyl‐L‐glutamate) film calculated from the above theoretical constants along with a composite theory is found to agree reasonably with experiment.
Molecular rheology of concentrated polymer systems. I
Authors: Doi Masao
Published: April 2003

The primitive chain model of Doi and Edwards is generalized to include the short‐time relaxation process. Stress relaxation after a sudden imposition of strain is studied in detail. It is shown that in the linear region (small strain) stress relaxation occurs in two steps, the relaxation of chain segments between the fixed entanglement points, and the relaxation of the entanglement points, in accordance with the conventional picture, whereas in the nonlinear region (large strain) there appears a new relaxation process between the above two. The characteristic time of this process is the Rouse relaxation time which the entire chain would have if there were no entanglements, and increases with the square of the molecular weight. This result is consistent with experimental observations.
Small‐angle X‐ray and neutron scattering studies of the morphology of ionomers
Authors: Roche E. J. , Stein R. S. , MacKnight W. J.
Published: April 2003

Preliminary small‐angle neutron scattering (SANS) studies have been made of different ionomers in the dry state and after saturation with water. Scattering from the dry samples arises from differences in the neutron scattering cross sections of the ionic and nonionic units in the polymer. The SANS technique is complementary to previous small‐angle x‐ray scattering (SAXS) studies since the SANS contrast differences are generally quite different than those for SAXS. A quantitative comparison is made of SANS and SAXS intensities for a dry cesium salt of an ethylene‐methacrylic acid (E‐MAA) copolymer. For water‐saturated samples the technique of isotopic replacement can be used in conjunction with SANS since saturation can be effected with either H2O or D2O. In this case information about the chemical composition of the phases is obtained from an analysis of the intensity ratio I/I. Results are consistent with the presence of a separate phase containing water molecules and ions in a matrix of the nonionic units. A Guinier analysis gives a radius of gyration of 17 Å for a water‐saturated cesium salt of an E‐MAA copolymer.
Nylon‐6 α‐phase crystal: Chain repeat distance and modulus in the chain direction at low temperature
Authors: Miyasaka Keizo , Isomoto Tsuneyuki , Koganeya Hiroshi , Uehara Katsuhiko , Ishikawa Kinzo , Ogata Nobuo
Published: April 2003

The chain repeat distance in the α‐phase crystal of nylon‐6 was measured from −150 to 150°C. The distance increases with decreasing temperature, indicating that the chain is not a complete planar zigzag but is twisted at room temperature. The relation between the distance and temperature changes at about −110°C and again near 40°C. Both changes seem to be related to the mechanical dispersions of the material. Young's modulus in the chain direction is 270 GN/m2 at −150°C, or 14% less than the theoretical value given by Tashiro and Tadokoro for the planar zig‐zag structure. It is not possible to determine from the (0k0) diffraction intensities whether the amide or methylene moieties are the more important in the chain twisting.
Glass transition in polyacrylonitrile: Analysis of dielectric relaxation data
Authors: Gupta A. K. , Chand Navin
Published: April 2003

Dielectric relaxation of polyacrylonitrile (PAN) samples, in which the presence of an amorphous phase is evidenced by x‐ray diffraction, has been studied over the temperature range 30–150°C and frequency range 102–105 Hz. These data as well as those reported by other authors, reveal several points useful to the understanding of the dielectric relaxations of PAN in relation to its structure. A glass transition in PAN is evidenced by at least two of the four data sets investigated; the third shows combined effect of two relaxations, whereas the fourth clearly shows a relaxation process different from the glass transition. The glass‐transition behavior of the dielectric relaxation data is confirmed by Williams‐Landel‐Ferry theory and a recent theory of Phillips, both of which lead to consistent conclusions.
Oriented cellulose films and fibers from a mesophase system
Authors: Chanzy H. , Peguy A. , Chaunis S. , Monzie P.
Published: April 2003

Cellulose mesophases were obtained by preparing concentrated solutions of cellulose (20–55%) in a mixture of N‐methyl‐morpholine N‐oxide (MMNO) and water. The anisotropy depends on four interconnected parameters: the temperature of the solution which, in general, must be lower than 90°C; the concentration of cellulose which must exceed 20%; a water content such that the mole ratio water/anhydrous MMNO is smaller than unity; and the degree of polymerization of the dissolved cellulose. The anisotropic cellulose solutions can readily be oriented during extrusion or casting thus giving fibers or films which upon regeneration exhibit high orientation.
Electron microscopy study of the structure of normal and abnormal poly(butylene terephthalate) spherulites
Authors: Roche E. J. , Stein R. S. , Thomas E. L.
Published: April 2003

Normal and abnormal spherulites of polybutylene terephthalate cast from solution in HFIP were investigated by electron microscopy (CTEM and STEM). Both spherulite types crystallize in the α form. The crystallite is biaxial with its greatest polarizability directions Z and Y oriented along the molecular chain and perpendicular to it in the plane of the terephthalate residue. In the normal spherulites, the [210]* direction is parallel to the radius direction, so that both Z and Y directions are oriented tangentially (negative spherulites). In the abnormal spherulites, the [111]* direction is parallel to the radius, and this explains the observed abnormal light scattering pattern.
Nature of the penetrant jump length in diffusion within polymers
Authors: Pace R. J. , Datyner A.
Published: April 2003

Results from two types of experiments, both on polyethylene, which allow, respectively, direct and indirect estimates of the magnitude of simple penetrant diffusion jump lengths are examined. In both cases the jump lengths inferred, for several small penetrants, are consistent with the values suggested by a recently proposed theory of diffusion in polymers.
Hydrostatic extrusion of linear polyethylene: Effects of extrusion temperature and polymer grade
Authors: Hope P. S. , Gibson A. G. , Ward I. M.
Published: April 2003

The hydrostatic extrusion behavior of linear polyethylene has been examined for two homopolymers of very different molecular weight characteristics and for a copolymer. Good unflawed extrudates could be obtained in all cases, and the extrusion behavior at a fixed temperature correlated well with the melt flow index. Although the maximum values of axial Young's modulus obtainable from the higher molecular weight homopolymer and the copolymer were lower than those possible for the lower molecular weight homopolymer, such materials do show improvements in creep behavior which could be advantageous. The effect of temperature on the extrusion behavior is discussed; the results suggest that for each grade of polymer there is an optimum temperature for effective extrusion, i.e., extrusion which gives optimum modulus enhancement. Finally, the melting behavior and the temperature dependence of the axial Young's moduli of the extrudates are considered in terms of our present knowledge of the structure of these high modulus materials.
Glass transition in semicrystalline polycarbonate
Authors: Wissler G. E. , Crist B.
Published: April 2003

The intensity of the glass transition in semicrystalline polycarbonate was measured by differential scanning calorimetry and by thermally stimulated discharge of electrets. Solution‐cast and bulk‐crystallized samples possessing widely varying crystallinities and morphologies were investigated. It is shown that the intensity of the glass transition is governed by the extent of primary crystallization and is a linear combination of intensities from the bulk amorphous regions and from noncrystalline polymer within semicrystalline aggregates such as spherulites. The intensity of the glass transition within spherulites is about 0.1–0.3 as great as that in bulk amorphous regions. A three‐phase model incorporating two distinct types of noncrystalline polycarbonate is proposed to account for the properties of this polymer.
Free‐volume interpretations of self‐diffusion in ternary solutions: n‐Paraffin‐hexafluorobenzene‐cis‐4‐polybutadiene
Authors: Ferguson R. D. , von Meerwall E.
Published: April 2003

Self‐diffusion of both diluents in the systems n‐paraffin + hexafluorobenzene + cis‐4‐polybutadiene (paraffin = dodecane or hexatriacontane) has been measured at 80°C as function of both concentrations, using field‐gradient spin‐echo techniques (1H and 19F NMR). The data follow the free‐volume model in the form of the Fujita‐Doolittle equation, or the Vrentas‐Duda theory, extended to apply to ternary systems. It is found that the polymer molecular jumping segments are roughly equal in size to the diluent molecules or their jumping segments.
Morphology and melting behavior of semicrystalline poly(ethylene terephthalate). II. Annealed PET
Authors: Groeninckx G. , Reynaers H.
Published: April 2003

Annealing of poly(ethylene terephthalate) samples crystallized under isothermal conditions above the crystallization temperature has a marked influence on their morphology and results in increased thermal stability of the crystalline structure as indicated by the melting point increase of the samples. The morphological transformation processes induced by annealing are very complex and depend on the thermal history of the samples, i.e., crystallization temperature and heating procedure. Depending on the nature of the processes occurring during annealing, various parameters characterizing the semicrystalline state of the samples can be affected such as the degree of crystallinity, the long spacing, the thickness of amorphous and crystalline layers, the crystal perfection, the fold‐surface structure, and the mosaic structure of the crystalline lamellae. Annealing involves a solid‐state transformation of the original crystalline structure including crystal perfection without thickening or a melting followed by recrystallization with crystal perfection and crystal thickening. The combination of differential scanning calorimetric (DSC) measurements and small‐angle x‐ray scattering is a powerful analytical tool to detect morphological changes and helps in deciding on the processes which are involved in the transformation of the microstructure upon annealing.
Electron spin resonance study of copolymerization of hexafluoroisobutylene with vinylidene fluoride
Authors: Yue H. , Nelson G. , O'Brien K. , Chandrasekaran S. , Sibilia J.
Published: April 2003

The Copolymerization reaction of hexafluoroisobutylene (HFIB) and vinylidene fluoride (VF2) was studied using X‐band electron spin resonance (ESR) by applying a photo‐in situ method. Owing to the toxicity of HFIB monomer, the flow ESR method could not be directly applied without extensive modification. The observed ESR signal with 21‐line hyperfine structure was assigned to the copolymer radical with head‐to‐head configuration. Although the HFIB monomer radical possesses the same hyperfine pattern, the ambiguity has been removed by using CF3 as an initiator radical. Owing to the high steady‐state concentration of the observed copolymer radical with head‐to‐head configuration as well as the nature of the static photo‐in situ ESR method, we believe the actual molecular configuration for HFIB/VF2 copolymer must be head‐to‐tail. The observed hyperfine constant for AβF = 1.74 mT suggests that the geometry for HFIB/VF2 copolymer radicals with both head‐to‐head or head‐to‐tail configurations is possibly similar to that of (CF3)3C· radical. The small value for AβH indicates steric hindrance to rotation about the CαCβ bond, and this is also supported by the experimental results of nonalteration in linewidth during the temperature dependence study from −40 to about 90°C. Attempts to measure directly the monomer reactivities have been unsuccessful owing to the fact that not all the possible radicals were detected, but nevertheless the relative reactivities of VF2 and HFIB could be estimated. The relative reactivities of VF2 and HFIB monomers and the steric hindrance effect indicate that the conformation of the copolymer is head‐to‐tail; this has been further confirmed by infrared analysis.
Fourier‐transform infrared studies of polymer blends. III. Poly(β‐propiolactone)‐poly(vinyl chloride) system
Authors: Coleman M. M. , Varnell D. F.
Published: April 2003

Fourier‐transform infrared (FTIR) studies of the poly(β‐propiolactone) (PPL)‐poly(vinyl chloride) (PVC) blend system are presented. PPL‐PVC blends are observed to be incompatible in the molten (80°C) and solid (25°C) states, over the entire range of compositions. This is in marked contrast to our previous results of the poly(ϵ‐caprolactone)‐PVC blend system which was shown to be compatible in the amorphous state. The results of both studies are compared and discussed with particular reference to the detection of intermolecular interactions by FTIR and correlation with compatibility in polyester‐PVC blends. The role of the chemical interactions in the compatibilization of polymer blends is discussed in terms of thermodynamic considerations. Finally, it is well known that changes in refractive index of polymer blend compositions can cause frequency shifts of infrared bands, which are particularly relevant to the interpretation of residual peaks obtained by difference spectroscopy. The FTIR results of the PPL‐PVC blends are germane to this subject and are discussed.
Rigid backbone polymers. XI. Solution phase‐viscosity relationship
Authors: Aharoni Shaul M.
Published: April 2003

Using combined results of isothermal viscosity measurements and cross‐polarized light microscopy on four polyisocyanate/solvent systems, the following were demonstrated: (a) an anisotropic phase appears, associated with a shoulder in the viscosity curve, at a concentration v lower than the peak viscosity at v; (b) the inversion from anisotropic inclusions in an isotropic matrix to isotropic inclusions in an anisotropic matrix, occurs at concentrations v > v and (c) the attainment of a single phase, microscopically anisotropic, occurs at v > v; where the viscosity is decreasing but has not yet reached its minimum. When the experiments were repeated with changes in temperature, the following were observed: (a) within each single phase the viscosity drops with increased temperature; (b) in the biphasic range, the total viscosity η0 remains about constant in the concentration range ≤ and increases with temperature in the range v > v; (c) in the interval v > v of the biphasic range, at constant temperature an increase in concentration decreases η0, and at constant concentration, a decrease in temperature lowers η0. Qualitative explanations of the observations are proposed.
SAXS analysis of a linear polyester and a linear polyether urethane—interfacial thickness determination
Authors: Ophir Zohar , Wilkes Garth L.
Published: April 2003

A small‐angle x‐ray scattering (SAXS) investigation of two linear segmented polyurethanes was carried out to learn about the respective domain structure (morphology). Both urethanes had a hard segment of methylene‐bis(4)phenyl isocyanate (MDI) and butanediol. These two components comprised 28% by weight of each system. The soft segments differed in that one was a polyether (tetramethylene oxide, molecular weight 1000), while the other was a polyester (polytetramethylene adipate, molecular weight 1000). Both of these segmented urethanes were stored at room temperature for over 6 months prior to investigation. Using an automated Kratky camera, SAXS scans were made. By detailed analysis (using the computer program of Vonk) the average interfacial thickness E of the domains was determined by two approaches. The value of E for the polyester was 10–12 Å, while it was 5–7 Å for the polyether. Within the limits of the assumptions used for analysis, these data directly support the conjecture that polyether urethanes generally lead to better phase separation. Other aspects of the analysis provided further information on the morphological structure. Some cautionary comments are provided on the use of quantitative SAXS data obtained from these or similar systems.
Kinetics and equilibria of sulfur dioxide sorption in kapton polyimide
Authors: Koros W. J. , Patton C. J. , Felder R. M. , Fincher S. J.
Published: April 2003

The kinetics and equilibria of SO2 sorption in Kapton polyimide film have been measured at 25°C for pressures up to 58 cm Hg using a quartz spring balance. The observed equilibria are described well by the dual‐mode model for sorption of penetrants in glassy polymers. Observed hysteresis in sorption‐desorption cycling indicates that the diffusivity of SO2 increases markedly with increasing local penetrant concentration in the polymer. The concentration dependence of the effective average diffusion coefficient is described well by an expression from dual‐mode theory. The Langmuir component of the sorption population has an extremely low mobility compared to that of the Henry's law component; in fact, the so‐called “total immobilization” limiting case, which assigns a zero diffusion coefficient to this component, appears to be satisfactory under the conditions studied. These results, coupled with published results for other penetrants, suggest that the degree of immobilization of the Langmuir population depends to a great extent on the condensability and/or the molecular size of the penetrant. Predictions of the SO2 diffusion time lag and permeability in Kapton as functions of the upstream SO2 pressure are presented and discussed in terms of the dual‐mode theory.
Sequence distribution in ethylene‐propylene copolymers. II. The 13C NMR spectra, multad populations, and kinetic parameters
Authors: Smith Wendell V.
Published: April 2003

Monad, dyad, and triad populations have been derived from the 13C NMR spectra of eight ethylene‐propylene copolymers. Using these values, Kinetic parameters of the polymerization have been calculated, including conditional probabilities, and reactivity ratios. The fraction of propylene entering in an inverted order has been found to be about 20%. The copolymerization is dominated by the relatively large reactivity of ethylene. There is an alternating tendency for the two monomers which is evident both in the normal addition of propylene and the inverted addition. Penultimate effects do not play a significant role.
Effect of molecular weight on the diffusion coefficient of carbon dioxide in polystyrene
Authors: Toi Keio , Ohori Yuko , Maeda Yasushi , Tokuda Taneki
Published: April 2003

The permeability and time lag at pressures below 1 atm were measured for carbon dioxide in five polystyrene samples with different molecular weights at 25 to 40°C. The apparent permeability coefficient decreases with increasing carbon dioxide pressure and also decreases with increasing molecular weight of polystyrene, whereas the apparent diffusion coefficient calculated from time lag increases with pressure and is independent of molecular weight. Parameters for the partial‐immobilization model were determined from the apparent diffusion and permeation coefficients by using a nonlinear least‐squares optimization program without using sorption data. The results suggest that the void‐saturation constant C′H decreases as the molecular weight of the polymer increases or as the chain‐end free volume decreases. The significance of these observation and their interpretation is discussed in terms of free‐volume theory for glassy polymers.
Comparison of theory and experiment for diffusion in dilute polymer solutions
Authors: Vrentas J. S. , Liu H. T. , Duda J. L.
Published: April 2003

Results from a number of theories for the concentration dependence of the mutual diffusion coefficient in dilute polymer solutions are examined, and clarifications are made as to what forms of the equations for these theories should be used in comparisons with experimental diffusivity data. An evaluation of the available theories for the concentration dependence of the diffusivity under theta conditions is carried out using experimental diffusivity data taken using sharp fractions of polystyrene. It is concluded that the Pyun—Fixman theory appears to provide the most promising method for estimating the concentration dependence of the mutual diffusion coefficient in dilute polymer solutions at the present time.
Cold crystallization of polytetrafluoroethylene by γ irradiation
Authors: Takenaga Mitsuru , Yamagata Kyozo
Published: April 2003

Changes in density and in the corresponding degree of crystallinity with radiation dose are studied experimentally for γ‐irradiated polytetrafluoroethylene (PTFE) in the dose range from 1 X 103 to 1 X 109 R. The relation between the amorphous fraction and the radiation dose is derived from a quantitative analysis of cold crystallization by scission of polymer backbone chains. The characteristic radiation dose, at which one break occurs on the average per initial molecule, is estimated as about 3 X 104 R on the basis of a derived kinetic equation. The theoretical relation is modified by considering microvoids produced in the irradiated samples. The radii of microvoids in the form of spheres are evaluated as about 0.2 nm, and are also related to cage spheres relevant to the chain scission process. Good agreement between the modified theoretical relation and experimental data is attained over the entire range of radiation dose.
Dilute solution properties of a polybenzimidazole
Authors: Kojima Takakazu , Yokota Rikio , Kochi Masakatsu , Kambe Hirotaro
Published: April 2003

Light scattering and viscometric studies have been carried out on dilute solutions of a polybenzimidazole in N,N‐dimethylacetamide. The data, which span the molecular weight range 2.9 ≦ 10−4Mw ≦ 23.3, and the temperature range 290 ≦ T/K ≦343, yield the dependence of the mean‐square radius of gyration 〈s2〉LS, the second virial coefficient A2, and the intrinsic viscosity [η] on molecular weight Mw and temperature. The unperturbed mean‐square radius 〈s〉LS was calculated using experimental values of 〈s2〉LS and A2. It was found that excluded volume effects on 〈s2〉LS are very small. The unperturbed hydrodynamic chain dimension 〈s〉η was estimated by considering draining effects. A small value of the draining parameter was obtained. Analysis of the temperature dependence of A2 and [eta;] leads to the conclusion that this system approaches a lower theta temperature with increasing temperature. The steric factor σ = 〈s〉/〈s〉f, based on the value of 〈s〉f calculated for the polymer chain with free rotation, is nearly unity. Most of these properties can be interpreted in terms of long rotational units within the main chain.
Dynamics of noncrystalline polyethylene
Authors: Swaminathan K. , Tewari S. P.
Published: April 2003

An anisotropic dispersive continuum model for the collective modes of polyethylene of any degree of crystallinity is suggested. The model successfully explains the experimental results for specific heat of polyethylene of 100%, 84.1%, 74.5%, 45.9%, and 0% crystallinity in the temperature range 2.5–60 K, where the specific heat of amorphous polyethylene is markedly different from that of crystalline polyethylene. The variation of specific heat with degree of crystallinity can be obtained by varying only one parameter θ1 (characterizing the low energy cubic modes), keeping the other two parameters (characterizing the transverse and longitudinal chain modes) constant. Thus, in going from the crystalline to the amorphous state, it is essentially the interchain binding which is affected, the chain modes being left undisturbed. Using the calculated values of specific heat for varying degrees of crystallinity, the variation of θ1 with the crystallinity is reported. Observed high‐temperature specific heats for crystalline and amorphous polyethylene up to 300 K are also explained using additional optical modes. The anisotropic Mössbauer elastic scattering fraction (MESF) for polyethylene of different degrees of crystallinity in the temperature range 0–425 K is obtained. For a given degree of crystallinity there is marked anisotropy in MESF which increases with increase in temperature. For a given direction, longitudinal or transverse, there is a large difference between the MESF of 0% and 100% crystalline polyethylene, which also increases with the increase in temperature. It is quite possible that the MESF experiment may prove to be more sensitive than the usual method for the determination of degree of crystallinity.
High‐conversion emulsion polymerization in a continuous reactor: Predictions using smith–ewart kinetics
Authors: Friedman Emil M.
Published: April 2003

Smith–Ewart Case‐2 kinetics are applied to a continuous stirred tank reactor operating at steady state in the high and middle range of conversion. Above the conversion CD at which the monomer droplets disappear in a batch reaction, the predictions are surprising. The particle size is predicted to be inversely proportional to the effective soap concentration S and independent of mean residence time θ below CD it is predicted to be proportional to the one‐third power of θ and independent of S. Above CD the particle concentration should be proportional to the cube of S and independent of θ; below this it should be as predicted by previous workers. The expressions for conversion are also different above CD. A new, more instructive, derivation is used. Simple analytic expressions are given for commonly used breadth parameters of the particle size distribution. It is shown that when conversion is low, an approximation made by previous workers is invalid, in that the growth rate can no longer be considered continuous.
Application of the porous‐sphere hydrodynamic model to dilute polymer solutions
Authors: McDonnell Milton E. , Jamieson Alexander M.
Published: April 2003

The porous‐sphere model of Debye–Brinkman–Bueche is applied to predict the limiting frictional coefficient f0 and intrinsic viscosity [η] of polystyrene fractions in tetrahydrofuran and random protein coils in 6M guanidine hydrochloride. Following the formulation of Wiegel and Mijnlieff, the molecular permeability is modeled to increase exponentially as the square of the distance from the center of the molecule. A method is developed to obtain this permeability from the translational diffusion coefficient. The experimental values of f0 and [η] are in satisfactory agreement with the calculated values. Also, this analysis predicts values of the Mandelkern–Flory–Scheraga parameter for flexible coils which are significantly smaller than the minimum values permitted by the Kirkwood–Riseman theory. This is in accord with the experimental evidence.
New evidence for molecular entanglements
Authors: Plazek D. J. , Raghupathi N. , O'rourke V. M.
Published: April 2003

Torsional creep and creep recovery measurements have been made on a 56% polymer weight solution of an extremely high molecular weight polystyrene (M = 4.4 × 107) in tri‐m‐tolyl phosphate and on the polymer itself after recovery both from relatively dilute and more concentrated solution in benzene by freeze drying. Although viscoelastic steady state was not achievable, an anomalously shorter rubbery plateau in the response of the bulk polymer relative to its solution was indicated. On the basis of the assumed presence of physical entanglements of the threadlike molecules, which determine the length and height of the rubbery plateau, it was predicted and confirmed that the undiluted polystyrene recovered from dilute solution would have the highest and shortest creep compliance plateau.
Manifestation of microgel‐like particles of styrene‐ethylene dimethacrylate copolymers in solution in 1H and 13C NMR spectra
Authors: Spêváĉek J. , Duŝek K.
Published: April 2003

From the integrated intensities of 1H NMR bands it has been found that in solutions of styrene (St)‐ethylene dimethacrylate (EDMA) copolymers, a considerable part of the monomer units do not show directly in high‐resolution 1H NMR spectra and it is suggested that these monomer units form compact structures, probably acting as cores of microgel‐like particles. In 13C NMR spectra all monomer units are shown, including those which are part of the compact microgel structures. From a comparison of 1H NMR spectra with other analytical methods (elemental analysis, infrared spectra) it follows that the composition of the copolymer in the core of the microgel is the same as the overall composition of the copolymer. The content of the compact structures in the microgel increases with the content of the EDMA component. The results are discussed from the point of view of structural features and of the motional restrictions of the St/EDMA copolymers in CCl4 solution. The consequences for 1H NMR analysis of copolymer composition are also discussed.
Effects of memory on the coherent scattering function for the rouse–zimm model of dilute polymer solutions
Authors: Fesciyan Sezar , Jhon Myung S. , Dahler John S.
Published: April 2003

We study the effect of the memory function on the coherent scattering function of a dilute polymer solution, taking into account hydrodynamic interactions among the polymer segments. The line shape, given by a sum of two exponentials, is very accurate numerically for ka ≳ 3 (with a the length of a polymer segment) and for times such that ω0(k)t ≲ 1.5 [with ω0(k) the initial slope]. However, this approximation to the scattering function is not nearly so accurate at the smaller values of ka encountered in light scattering experiments. The amplitudes and relaxation times associated with the two exponentials are found to be markedly dependent on the strength of the hydrodynamic interactions.
Vibrational spectra and normal coordinate analysis of trans‐1,4‐poly(2,3‐dimethylbutadiene) and the two polymorphic forms of trans‐1,4‐poly(isoprene)
Authors: Petcavich R. J. , Coleman M. M.
Published: April 2003

The infrared and Raman spectra of the two polymorphic forms of trans‐1,4‐poly(isoprene) (TPI) and trans‐1,4‐poly(2,3‐dimethyl butadiene) (TPDMB) are presented. Infrared spectra of the alpha and beta forms of TPI were obtained by digitally subtracting the amorphous contribution from the corresponding spectra of semicrystalline TPI polymers. Normal coordinate calculations are presented for both polymorphic forms of TPI and TPDMB, and the assignments of the normal modes are discussed.
Side‐chain crystallinity, heat of melting, and thermal transitions in poly[N‐(10‐n‐alkyloxycarbonyl‐n‐decyl)maleimides] (PEMI)
Authors: De La Campa J. I. González , Barrales‐Rienda J. M. , Ramos J. González
Published: April 2003

The heat of melting, the melting temperatureTm, and the sub‐Tgtransition temperature have been studied from –120°C to aboveTmin a series of 11 poly[N‐(10‐n‐alkyloxycarbonyl‐n‐decyl)]‐maleimides (PEMI). Side‐chains from ethyl to n‐docosyl withneven have been included. The contribution to the heat of melting per methylene group shows that the hexagonal paraffin crystal modification is present in these poly(N‐maleimides), in agreement with x‐ray data for the same compounds. The enthalpy data show that only a part of the outer methylene groups are present in the crystalline aggregates. Furthermore, DSC traces exhibit a typical distribution of crystallite sizes, which become narrower as the side‐chains become longer. The critical chain length needed to form a stable nucleus includes nine methylene groups in the outer part of the n‐alkyl side‐chain. The influence of the side‐chain length and crystallinity on the γ‐transition temperature of these polymers was also investigated. In the range where these polymers are essentially amorphous the sub‐Tgtransition temperature decreases continuously as the number of methylene groups in the side‐chain increases. This transition is attributed to internal motion within the external side‐group without any interaction with the main chain. This is presumably made possibly by the partial rotation of the oxycarbonyl group. We suggest that this transition is similar to the well known γ transition which has been attributed to various segmental motions in all ethylene copolymers and in all homopolymers containing a determined number ofCH2units in the main‐chain or in the side‐chain. Estimates based on the chemical structure, yield a value for the γ transition of CH2similar to that measured by other methods in polyethylene and related materials.
Heat capacity of a polydiacetylene single crystal from 3 to 300 K
Authors: Engeln I. , Meissner M.
Published: April 2003

Heat capacities Cp of a polydiacetylene‐bis(toluene sulfonate) single crystal and its monomer have been measured in the temperature range from 3 to 300 K. The temperature dependence of Cp for both monomer and polymer crystals differs from that for monoatomic solids. By applying a chain lattice model for a polymer crystal, the temperature dependence of the heat capacity can be described assuming a phonon density of states given by bending and stretching modes of the polymer backbone. With a combination of one‐dimensional and three‐dimensional elastic continuum approximations, the heat capacity has been calculated and a good fit to the data has been obtained. A small peak in Cp was detected at 161 K for the monomer and at 198 K for the polymer. This may be ascribed to a lower‐temperature phase transition in the polydiacetylene crystals evidenced by previous x‐ray and spectroscopic measurements.
Incompatible blends: Thermal effects in a model system
Authors: Harrison Ian R. , Runt J.
Published: April 2003

There has been a growing interest in compatible blends in which one of the polymers is crystallizable. At appropriate compositions some of this polymer will crystallize, the remainder forms a compatible blend with the other polymer component; attempts have been made to relate melting point depression of the crystalline component to diluent effects, i.e., polymer/polymer interactions. Melting point is also a function of lamella thickness, the determination of which is very difficult in such systems. It is assumed in this type of study that the melting point of a crystal in an incompatible matrix will be unchanged. In an attempt to test this assumption we have determined the melting behavior of isothermally grown, single crystals of polyethylen (from the same preparation) embedded in a variety of incompatible matrices. The matrices used were polybutadiene, polystyrene, and polyphenylene oxide. This work shows that polymer single crystals embedded in an incompatible polymer matrix can show apparent melting point depressions of up to 5°. This size of depression represents a significant part of that reported for compatible systems.
Chemical analysis of vinyl‐crosslinked poly(dimethylsiloxane) model networks and use of the resulting structural information in the interpretation of their elastomeric properties
Authors: Llorente M. A. , Andrady A. L. , Mark J. E.
Published: April 2003

Model networks were prepared by selective crosslinking through vinyl groups occurring as either chain ends or as side‐groups on a poly(dimethylsiloxane) backbone. Iodometric titrations were used to determine the number of unreacted groups, thereby providing detailed information on the completeness of the reactions and the structure of the resulting networks. The end‐linking reaction of the vinyl‐terminated chains was generally found to be at least 95% complete. In the case of very high junction functionality, however, the extent of reaction was significantly lower, presumably because of steric interferences in the vicinity of the junctions, as was concluded in a previous investigation. Lower extents of reaction were also found in the case of vinyl groups located along the chains, probably because such groups are constrained by two chain sequences instead of one. The equilibrium elastomeric properties of both types of networks were interpreted using the structural information thus obtained and were found to be in good agreement with previous experimental results. They are also in satisfactory agreement with theory, without introduction of the highly questionable assumption of large contributions from interchain entanglements.
High‐resolution NMR spectra and phase equilibria in poly(phenylacetylene)‐diluent mixtures
Authors: Sanford T. J. , Allendoerfer R. D. , Kang E. T. , Ehrlich P.
Published: April 2003

The C‐13 NMR spectra of partly crystalline poly(phenylacetylene) (PPA) in CDCl3 CCl4 are rather well resolved and the peaks can be matched with those of 1, 3,5‐triphenylbenzene. A different, less‐well‐resolved C‐13 spectrum is characteristic of a disordered PPA obtained by heating. We conclude that crystalline PPA has the chain conformation of a cis‐cis‐oid helix. This interpretation is consistent with the proton NMR spectra and is supported by the fluorescence spectra, which can display two bands, one concluded to be characteristic of the cis‐cis‐oid conformation, the other of chain conjugation in the disordered polymer. Phase equilibria of PPA in the presence of chloroform were determined and are represented as those of the quasiternary mixture cis‐cis‐oid helix, disordered polymer, and chloroform.
Negative thermal expansion of polymer crystals: Lattice model
Authors: Chen F. C. , Choy C. L. , Young K.
Published: April 2003

The lateral thermal motion of atoms in an inextensible polymer chain would cause a shortening along the chain direction. This effect could explain the observed negative thermal expansivity α along the chain direction of a polymer crystal. Using this idea, the expansivity α is calculated for a lattice of parallel linear chains. A value of −1.3 × 10−5 K is obtained for chains with a carbon backbone, in good agreement with data for polyethylene.
Phase transformation in mixtures of polystyrene and poly(vinyl methyl ether)
Authors: Davis D. D. , Kwei T. K.
Published: April 2003

Homogeneous films comprised of mixtures of polystyrene and poly(vinyl methyl ether) can be obtained by evaporation from a ternary solution containing toluene as the solvent. Heterogeneous films result when the solvent is trichloroethylene. The possibility that a heterogeneous film cast from trichloroethylene can be transformed to a homogeneous one by physical means is a logical expectation when the polymer‐polymer interaction is favorable, though as yet no comprehensive report has appeared in the literature. We have accomplished the transformation by increasing the temperature. Optical microscopy and glass transition experiments were employed to observe the effects.
Small‐angle scattering studies of nafion membranes
Authors: Roche E. J. , Pineri M. , Duplessix R. , Levelut A. M.
Published: April 2003

The physical structure of Nafion membranes has been investigated by small‐angle neutron scattering (SANS) and small‐angle x‐ray scattering (SAXS). Samples in the acid form may exhibit two scattering peaks. The first, observed by SANS at an angle corresponding to a Bragg spacing of 180 Å, is shown to arise from structures in crystalline regions. A second peak at larger scattering angles is shown to arise from ion‐containing regions which may be swollen with water. Salt‐form samples made by soaking the acid form in an aqueous salt solution can also exhibit the same two scattering signals. But in amorphous salt‐form samples produced by quenching from the melt the first peak is absent. This permits a more accurate study of the second peak by SAXS, which shows that the second scattering component is present as a maximum over a wide range of water contents but is absent in a sample dried at 200°C. The position of the peak shifts to lower scattering angles (or larger spacings) at higher water contents. Possible structural models that might give rise to the maximum are discussed. A calculation of the SAX invariant is made and results are consistent with a phase separation of a large fraction of the water.
Comments on a paper by Axelson and Mandelkern concerning 13C NMR spectra of polymers
Authors: Boyer Raymond F. , Heeschen Jerry P. , Gillham John K.
Published: April 2003

It is shown that the 13C NMR spectral collapse temperatures Tc reported by Axelson and Mandelkern tend to give a constant ratio of Tc/Tg averaging 1.21 ± 0.05 and independent of Tg or of polymer structure. It is further shown that Tc is not a high‐frequency value for Tg because this would require Tc/Tg to decline with increasing Tg. Tc/Tg agrees in numerical value with Tu/Tg, where Tll is the liquid‐liquid transition lying above Tg. Direct comparison of Tc and Tu for four polymers PIB, PnBA, atactic PP, and isotactic PMMA shows very close agreement. The various results suggest, but do not prove, that Tc from 13C NMR spectroscopy may be a new, direct measure for Tll. A measured Tc of 233K for linear PE is compatible with a Tg near 195 K (233/195 = 1.19), whereas a Tg of 148 K gives the ratio 233/148 = 1.57, which is outside any value shown in tabulated form.
Crystallization of poly(α‐methyl‐α‐N‐propyl‐β‐propiolactones) prepared from homogeneous and heterogeneous initiators
Authors: Grenier Daniel , Leborgne Alain , Spassky Nicolas , Prud'homme Robert E.
Published: April 2003

Half‐crystallization times t½, enthalpies of fusion ΔH, melting temperatures Tf glass transition temperatures Tg x‐ray patterns, and morphologies were obtained for nine samples of poly(α‐methyl‐α‐n‐propyl‐β‐propiolactones) prepared from different homogeneous or heterogeneous initiators. The bulk of the results indicates that all samples can be classified into two categories: Polymers A having t½≏, 100 min, ΔH ≏ 26 J/g, T ≏ 376 K, Tg ≏ 275 K, and Polymers B having t½ ≏ 10 min, ΔH ≃ 14.5 J/g T ≏ 425 K and Tg ≏ 271 K. Polymers A were prepared with homogeneous initiators while polymers B were polymerized with heterogeneous intiators. The difference in crystallization behavior between polymers A and polymers B is certainly due to a difference in microstructure, brought about by the initiators, which has been qualitatively observed by NMR.
Small‐angle light scattering by random assemblies of incomplete spherulites. Systems with partial degree of volume filling
Authors: Tabar R. J. , Wasiak A. , Hong S. D. , Yuasa T. , Stein R. S.
Published: April 2003

A theory is presented to account for the effect of the impingement of growing spherulites on theirHvsmall‐angle light scattering patterns. The theory is developed on the basis of results of computer‐simulated two‐dimensional spherulite growth and calculated scattered intensities. The impingement produces a lowering of the intensity of the scattering maximum and the diminishing of the overall sharpness of the scattering peak. The extent of these effects increases with area fraction of spherulites. A procedure is suggested for determining correction factors that may be applied to intensity data obtained during the course of spherulite crystallization. An interpretation is made of the type of average spherulite size determined from the scattering angle of maximum intensity.
Component analysis of proton NMR spectra of linear polyethylene in the α‐transition temperature range and phase distribution
Authors: Horii Fumitaka , Kitamaru Ryozo
Published: April 2003

Broad‐line 1H NMR spectra of linear polyethylene at temperatures in the α‐transition range can be analyzed in terms of contributions from the crystalline and noncrystalline components provided molecular motion in the crystalline region is adequately considered. The spectrum of solid n‐C32H66 or n‐C44H90 prior to melting is used to take account of the contribution of the crystalline region of the polymer to molecular motions. The temperature dependence of the component distribution in the polymer is briefly discussed for a wide range of temperatures, together with previously reported results at low temperatures. The noncrystalline component is in a rigid glassy state at very low temperatures but with rising temperature it transforms to a mobile glassy state with restricted molecular motion, and transforms partially to the rubbery state at high temperature. The crystalline component remains rigid at low temperature, but some molecular motion is associated with it at higher temperatures in the α‐transition range.