bluuebunny/crossref_metadata_2025 huggingface dataset:
Photophysical properties of N‐acylated linear polyethylenimine and dehydroalanine main‐chain polymers containing carbazole or pyrene groups in side chains
Authors: Arora Kartar S. , Overberger C. G. , Johnson G. E.
Published: April 2003

A comparison of the UV absorption spectra of a carbazole‐substituted N‐acylated linear polyethylenimine (PEI) (5, 6) with its monomer (1, 2) and dimer (3, 4) model compounds shows the presence of local conformational order of the carbazole groups in 3, 5, and 6 since these compounds exhibit hypochromism. The UV absorption spectra of carbazole‐substituted N‐acrylated dehydroalanine main‐chain polymer (PDA) (12, 13) and monomer (10, 11) model compounds indicate that the extent of local conformational order of the carbazole groups is reduced in 12 and 13 compared to that in 5 and 6. The UV absorption spectra of a pyrene‐substituted PEI (9) and PDA (15) and those of their monomer model compounds (7, 14) indicate that the extent of local conformational order of the pyrene groups is greater in 9 than in 15 and furthermore the pyrene‐substituted polymers (9, 15) show more local conformational order than analogous carbazole‐substituted polymers (5, 12). The emission spectra of 5 and 12 show carbazole monomer emission, while those of 9 and 15 are dominated by pyrene excimer emission. The formation of excimer emission is more efficient in 9 than in 15. Fluorescence lifetime measurements indicate interactions of excited carbazole groups in 5 and 13 but not in 12. The quenching of carbazole fluorescence by dimethyl terephthalate is more efficient in 5 than that in 12, indicating more efficient transfer of electronic energy in 5. These measurements show that the PEI main‐chain polymers are conducive to interactions of the pendant groups.
A study of molecular motion in a liquid‐crystalline copolyester by broad‐line nuclear magnetic resonance
Authors: Clements J. , Humphreys J. , Ward I. M.
Published: April 2003

Broad‐line nuclear magnetic resonance (NMR) measurements have been carried out for the proton resonance in an oriented liquid‐crystalline copolyster prepared from 4‐hydroxybenzoic acid (HBA) and 2‐hydroxy‐6‐naphthoic acid (HNA). The Second moments were determined as a function of the angle γ between the specimen orientation direction and the static magnetic field. The low‐temperature NMR results are consistent with a rigid structure of random copolymer chains arranged on a hexagonal lattice. As the temperature is raised the NMR signal changes and can be modeled very satisfactorily by considering that there is free rotation of the benzene ring residues about the 1‐4 substitution direction. At more elevated temperatures the observed NMR spectra are consistent with rotation of both HBA and HNA groups.
Effect of pressure on phase behavior in polymer blends of poly(2,6‐dimethyl‐1,4‐phenylene oxide) and poly(styrene‐co‐p‐fluorostyrene) copolymers
Authors: Maeda Yoji , Karasz Frank E. , MacKnight William J. , Vuković R.
Published: April 2003

The effect of pressure on the miscibility of blends of poly(2,6‐dimethyl‐l,4‐phenylene oxide) (PPO) with a random copolymer of styrene and para‐fluorostyrene, P(S‐co‐p‐FS), has been studied by high pressure differential thermal analysis (HPDTA). P(S‐co‐p‐FS) copolymers less than 36 mole % p‐FS are miscible with PPO in all proportions irrespective of pressure up to 200 MPa, using the customary criterion of a single calorimetric glass relaxation. P(S‐co‐p‐FS) copolymers containing 40 to 50 mole % p‐FS undergo phase separation upon annealing at elevated temperatures, indicating the existence of a lower critical solution temperature (LCST). In these blends, pressure displaces the phase boundary associated with the LCST to higher temperatures causing an apparent increase in polymer miscibility. The phase diagram for the blend of PPO and P(S‐co‐p‐FS) containing 46 mole % p‐FS, shows that the critical composition at about 50 wt % PPO does not change with pressure, but the consolute temperature Tc increases with increasing pressure. The pressure dependence of the LCST (dTc/dP) of this system is about 0.35°C/MPa.
Structure and properties of polypropylene crystallized from the glassy state
Authors: Hsu C. C. , Geil P. H. , Miyaji Hideki , Asai Kenjiro
Published: April 2003

Glassy isotactic propylene (PP) films of thickness up to 0.3 mm were obtained by an ultraquenching technique. The structure and properties of the as‐quenched and subsequently crystallized samples were characterized by various techniques. Electron microscopy indicates the glass has no structure larger than 25 Å. X‐ray diffraction shows PP crystallizes from the glass into a smectic structure at ca. −20°C and then transforms to monoclinic microcrystals at ca. 40°C; a nodular structure (80 to 100 Å in diameter) was observed on the surface. The transformation temperature increases with the film thickness. Annealing above the α‐relaxation temperature results in an increase in the nodule size. A correspondence was found between the diameter of the nodules observed on the surface and long spacings obtained by small‐angle X‐ray scattering from the bulk. Dynamic mechanical spectra show the presence of two relaxation‐like peaks at ca. −10°C and 10°C for the as‐ultraquenched samples. X‐ray scattering, differential scanning calorimetry (DSC), and torsion pendulum measurements show PP crystallizes from the glass at a temperature, depending on the rate of heating, that corresponds to the lower relaxation peak temperature.
Initial relaxation times in dynamic light scattering from once‐broken rod molecules in solution
Authors: Moro Keiji , Fujiwara Masako
Published: April 2003

Initial relaxation times determined by the initial decay rate of the time correlation function of scattered light are calculated for the once‐broken rod model (two rigid rods of equal length connected by a universal joint) following the Fujiwara–Saito theory. The coefficient C describing the initial angular dependence of the first cumulant of the correlation function is also calculated. The results are compared with Pecora's results based on the Yu–Stockmayer theory for this model; and it is shown that the Fujiwara–Saito theory gives reasonable results.
Properties of polyelectrolytes: Maleic acid‐vinylpyrrolidone copolymers. I. Viscometric behavior in dilute solution
Authors: Rios Hernan , Gargallo Ligia , Radić Deodato
Published: April 2003

The viscometric behavior of maleic acid‐vinylpyrrolidone copolymer systems p(MA–co–VP) were studied in dilute solution. The weight‐average molecular weights of fractionated copolymers were determined by gel permeation chromatography. Viscometric relations were determined in aqueous salt solutions and in organic solvents. Two theta‐conditions were found for p(MA–co–VP): in 0.968 M Na2SO4, and in a DMSO/acetone mixture, 35.6/56.4 (v/v) at 25°C. The conformational and thermodynamic parameters KΘ and B were evaluated from viscosity data in good solvents using the Stockmayer–Fixman and Berry extrapolations. A linear variation of B with the salt concentration was observed. The electrostatic (Be) and nonelectrostatic (Bo) contributions to B were estimated. It was found that Be > Bo, and this was attributed to the hydrophylic nature of p(MA–co–VP) copolymers. The latter would reflect a greater influence of the electrostatic interaction on the hydrodynamic behavior of this polymer. The electrostatic (α), and the nonelectrostatic lim →∞(α3 − 1) contributions to the expansion factor α were determined. It was found that α is a function of (M̄w/Cs)1/2, as is predicted by the Fixman theory.
Micromechanics of a craze zone at the tip of a stationary crack
Authors: Bevan L. , Doell W. , Koenczoel L.
Published: April 2003

The finite element method is applied to contours (measured by interferometry) of craze zones in front of stationary crack tips in polymethylmethacrylate (PMMA) in order to compute the stress distribution. The stress along the craze zone has its maximum at the crack tip, being about twice that predicted by the Dugdale model; and it decreases at first sharply and then more gradually, being almost constant as the craze tip is approached. Stress distributions, in a growing craze at the still stationary crack tip, at various times can be combined in a normalized curve. Craze stresses relax with time as the craze continues to propagate in a stable manner. When the specimen is unloaded, the craze stress is compressive near the crack tip, but is tensile at the craze tip and for most of the craze length. Analysis of measurements made during a loading cycle establishes minimum stress intensity levels at which no fibrils are in compression. The levels are different for increasing and decreasing loads, and it is found the craze stresses are tensile for most of the cycle. Throughout the cycle, there is an excellent correlation between the average craze stress and the theoretical stress predicted by the Dugdale model.
High‐melting bisphenol‐A polycarbonate from annealing of vapor‐induced crystals
Authors: Jonza James M. , Porter Roger S.
Published: April 2003

Polycarbonate is known to crystallize thermally, but only slowly and to a limited (25%) extent. The melting points reported exhibit a wide variation. We have found that the melting temperature of polycarbonate may be drastically increased by employing a sequence of vapor‐induced crystallization and annealing treatments. The crystals formed by the treatment with organic vapor act as a nucleation or precursor state for further crystallization into larger, more perfect lamellae. An initial peak melting temperature of 195°C has been annealed up to 239°C, and then to 295°C by a double‐heat treatment. This sample is 60% crystalline, based on heat‐of‐fusion calculations. An equilibrium melting point of 335°C has been obtained for PC from an extrapolation of reciprocal lamellar thickness.
Prediction of thermodynamic properties of polymer solutions by a group‐contribution method
Authors: Patwardhan Ashutosh A. , Belfiore Laurence A.
Published: April 2003

The Flory–Huggins lattice‐theory expression for solvent activity in a polymer‐solution is commonly used to calculate the thermodynamic interaction parameter χ with the aid of experimental data from vapor pressure osmometry. This expression assumes that χ is independent of composition. However, experimental data for a variety of polymer‐solvent mixtures indicate that χ exhibits an appreciable concentration dependence. A group contribution method, UNIFAC (UNIQUAC Functional‐Group Activity Coefficients) incorporating the free‐volume correction of Oishi and Prausnitz is used to predict the dependence of χ on solvent concentration. Agreement with previously reported experimental data is within 15%. Calculated values of χ obtained from the Flory–Huggins expression for solvent activity and from the corresponding Gibbs free energy of mixing (which does not assume that χ is independent of composition) are compared. Calculations based on the Gibbs free energy of mixing predict a somewhat larger value of χ relative to those based on solvent activity. The specific Gibbs free energy of mixing for polystyrene‐solvent mixtures is calculated using the UNIFAC model, and is found to represent qualitatively the phase equilibrium behavior. Quantitative discrepancies are observed, however, for the polystyrene‐acetone system in light of the actual experimental solubility reported by Suh and Clark (20). Most of the thermodynamic predictions for polymer‐solvent systems investigated herein are correlated qualitatively with the relative mismatch between solubility parameters of both components.
The effects of morphological transitions on hydrogen bonding in polyurethanes: Preliminary results of simultaneous DSC–FTIR experiments
Authors: Koberstein Jeffrey T. , Gancarz Irena , Clarke Thomas C.
Published: April 2003

The influence of morphological transitions on the hydrogen‐bonding behavior of polyurethanes is investigated by simultaneous measurements of Fourier‐transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC). The materials examined are a noncrystalline polyurethane hard segment, a crystallizable polyurethane hard segment, and a segmented polyurethane block copolymer containing crystallizable hard segments. Integrated absorbance data show that the hydrogen‐bonding behavior is insensitive to crystalline transitions within the hard segment microdomains, but that it does reflect morphological transitions in the block copolymer that are associated with intersegmental mixing. In addition, the spectral data show conclusive evidence for reversal of the urethane reaction at high temperatures.
The concentration dependence of the compression modulus of iostactic polystyrene/cis‐decalin gels
Authors: Guenet J. M. , McKenna G. B.
Published: April 2003

New results for isotactic polystyrene/cis‐decalin gels are presented that suggest that a simple fringed micellar model of the gel may not be appropriate. In measuring the room temperature compressive modulus of gels formed at −20°C, it was found that, not only do the gels exhibit significant stress relaxation but also that the isochronal modulus‐concentration diagrams exhibit abrupt changes in modulus (reduced stress) over narrow ranges in concentration rather than the smooth curves (straight lines) typical of swollen rubber and fringed micellar gels.
Analysis of trichroic infrared absorption in solids. I. Description of methods
Authors: Fina L. J. , Koenig J. L.
Published: April 2003

Infrared absorption by polymeric solids is generally anisotropic due to orientational effects induced by industrial processing and fabrication. The isotropic‐equivalent or structure‐factor spectrum of a sample can be computed from the absorbances along the three principal axes of the absorption ellipsoid. Experimentally, this is accomplished by a tilting procedure which has been computer interfaced for precise angular control. The technique is applied to poly(vinyl acetate) (PVAc) and poly(ethylene terephthalate) (PET). The effects of refractive index dispersion, fringe distortion, reflection, and birefringence are evaluated in terms of the thickness direction calculation. Error spectra based on sample symmetry are generated, and the limits of accuracy of the tilting technique are established.
The role of chain scission in fracture of amorphous polymers
Authors: Willett J. L. , O'Connor K. M. , Wool R. P.
Published: April 2003

We have investigated the role of chain scission in glassy polymers by monitoring the molecular weight changes induced by microtoming thin slices of monodisperse polystyrenes. The changes in number‐average molecular weight allow determination of Nf, the number of bond scissions per unit area. It is found that Nf is independent of initial molecular weight and has the value 6.50 × 1013 scissions/cm2 at room temperature; Nf decreases with increasing temperature, suggesting that chain pullout increases with temperature. The work required to create unit surface area in polystyrene is several orders of magnitude greater than the energy required to break Nf bonds, indicating that plastic deformation plays a major role in deformation and fracture of glassy polymers.
Electrical conduction of poly(vinyl alcohol) films
Authors: Tawansi A. , Migahed M. D. , El‐Hamid M. I. A.
Published: April 2003

PVA films (30–45 μm thickness) were prepared by casting. dc electrical measurements were done over the temperature range 293–353 K. Two different conduction mechanisms are suggested. The first one is ohmic and extends to 303 K. Above this temperature a space‐charge‐limited conduction mechanism, with protons as charge carriers, predominates. Dependences of the voltage‐reversion current temperature and field were investigated and were attributed to a clean‐up effect of charge carriers. The variance in the activation energy, calculated from the conductivity curves and from the mobility curves, led to a discussion of the origin of the charge carriers. No change in conductivity was observed for the PVA films irradiated with UV (of wavelength 365 nm) at 303 K, i.e., PVA is a photostable material under these conditions.
Fourier‐transform infrared study of orientation in pure and plasticized poly(vinyl chloride)
Authors: Theodorou M. , Jasse B.
Published: April 2003

Fourier‐transform infrared spectroscopy has been used for the study of orientation of pure and plasticized PVC. The results show that orientation is independent of experimental conditions (temperature, strain rate, plasticizer) in the homogeneous deformation range. Such behavior is explained by the existence of a fringe micellar‐type network with physical crosslinks. The network is partially destroyed during stretching. Furthermore, the orientation of the carbonyl group of the plasticizer is connected with PVC chain orientation.
An analysis of the secondary relaxation in isochronal measurement of glasses
Authors: Chung S. H. , Pathmanathan K. , Johari G. P.
Published: April 2003

A method by which the occurrence of a secondary relaxation can be deduced from the isochronal dielectric and mechanical loss data of amorphous and crystalline materials is given. The method eliminates the complexity arising from the frequency‐independent, temperature‐dependent background loss in solids.

It is shown that the relaxation rate measured at a fixed frequency by varying the temperature substantially differs from that measured at a fixed temperature by varying the frequency when the strength of the relaxation is temperature dependent. This discrepancy leads to a different value of activation energy and of preexponential factor when the strength increases with temperature. The results are discussed in terms of the temperature dependence of the strength of relaxation and its distribution parameter.

The method of analysis has been applied to the data for a molecular and a polymeric glass and shows the occurrence of a β process which is otherwise not detected in their tan β isochrones. Experimental data on a wide variety of glasses also show that the activation energies and relaxation rates obtained from isochrones differ from those obtained from the isothermal spectrum.
Direct method of calculating the dynamic scattering spectrum
Authors: Wei Gaoyuan , Cohen Claude
Published: April 2003

A method of obtaining the scattering spectrum that bypasses the need to solve for the configurational distribution function of the macromolecules is presented. It involves the direct calculation of averages that appear in the structure factor expression. Application of the method to Rouse coils recovers Pecora's classical results. The method is applied to obtain the coherent spectrum of a solution of “encapsulated” dumbbells for which the configurational distribution is not available.
Synthesis and bulk physical properties of styrene‐alkoxide ionomers. Part I: Sodium salts of polystyrene‐co‐4‐hydroxystyrene
Authors: Clas S.‐D. , Eisenberg A.
Published: April 2003

Polystyrene‐co‐4‐hydroxystyrene ionomers (3.0–22 mol%) were synthesized via neutralization of demethylated polystyrene‐co‐4‐methoxystyrene. The physical properties of the ionomers as well as their nonionic precursors were studied by calorimetry, torsion pendulum and small‐angle X‐ray scattering (SAXS). Evidence for ion aggregation was obtained for the styrene‐4‐hydroxystyrene ionomers from SAXS and torsion pendulum studies.
Synthesis and bulk physical properties of styrene‐alkoxide ionomers. Part II: Sodium salts of polystyrene‐co‐4‐hydroxymethylstyrene
Authors: Clas S.‐D. , Eisenberg A.
Published: April 2003

Polystyrene‐co‐4‐hydroxymethylstyrene ionomers (2.5–19.4 mol%) were prepared from the partial chloromethylation of polystyrene, followed by esterification, saponification, and finally neutralization. The physical properties of the ionomers as well as their nonionic precursors were studied by calorimetry, torsion pendulum, and small‐angle X‐ray scattering (SAXS). SAXS and torsion pendulum studies show no evidence of extensive clustering.
Styrene‐alkoxide ionomers. Part III: Comparison with other styrene ionomers
Authors: Clas S.‐D. , Eisenberg A.
Published: April 2003

The properties of two novel ionomers, the sodium salts of styrene‐4‐hydroxystyrene and styrene‐4‐hydroxymethylstyrene, obtained from torsion pendulum experiments are compared with those of other styrene ionomers. The glass transition temperature of the matrix, the size of the ionic aggregates, and the strengths of the ionic interactions within these large aggregates were related to the type and position of the ionic group. Attempts were made to explain these results.
The liquid‐crystalline properties of (acetoxypropyl)cellulose: Effect of chain length and degree of acetylation
Authors: Laivins G. V. , Sixou P. , Gray D. G.
Published: April 2003

Partially degraded (hydroxypropyl)cellulose methanolysates were acetylated in an acetic anhydride/dioxane mixture with a perchloric acid catalyst, yielding (acetoxypropyl)cellulose (APC) samples with an unit ester content per anhydroglucose unit of three. Eight APC samples of molar masses from 10,000 to 1.8 × 105 g/mol were prepared. On heating, all the samples displayed biphasic behavior prior to isotropization. The isotropization temperature of the samples increased rapidly with molar mass, attaining a limiting value of 174°C. The substitution of hydroxyl groups of HPC by acetyl groups lowered the limiting value. Lyotropic mesophases of APC in dimethyl acetamide (DMAc) showed isotropization temperatures that increase nonlinearly with increasing APC concentration. For chains with contour lengths exceeding 72 nm, the critical concentration for mesophase formation, 0, does not depend on the chain length. However, for short chains the 0 value increases rapidly with decreasing chain length. The cholesteric reflection wavelength, λ0, of a thermotropic APC sample of low molar mass is greater than that of a higher molar mass sample at a given temperature and increases with increasing temperature for all samples. Partially acetylated (hydroxypropyl)cellulose displays reflection colors at lower temperatures than the fully acetylated APC.
Polydispersity effects on diffusion in polymers: Concentration profiles of d‐polystyrene measured by forward recoil spectrometry
Authors: Mills Peter J. , Green Peter F. , Palmstrøm Christopher J. , Mayer James W. , Kramer Edward J.
Published: April 2003

Forward recoil spectrometry is shown to be a useful technique for measuring diffusion of d‐polymer chains in h‐polymer melts. Concentration profiles of a deuterated diffusing species may be determined with a depth resolution of 80 nm and a sensitivity of 0.1 vol % d‐polymer in h‐polymer. Consequently diffusion coefficients as small as 10−16 cm2/s can be readily measured. If polymer chains diffuse by a reptation mechanism, the concentration profile ø(x) of diffusing polydisperse polymer should be quite different from øm(x), the Fickian solution, which one obtains for monodisperse polymer. This idea was tested by measuring ø(x) of polydisperse d‐polystyrene (d‐PS) diffusing into h‐PS. The results are in excellent agreement with the ø(x) predicted from the reptation model and the experimentally determined molecular weight distribution.
Ionic dissociation of ionene polymers in aqueous solutions
Authors: Fujii Michihiro
Published: April 2003

The degree of ionic dissociation of aliphatic ionene polymers, 3,3‐, 4,4‐, 6,6‐, and 8,8‐ionene bromide in salt‐free aqueous solutions at infinite dilution was obtained by emf measurements with a bromide ion electrode. The results show that the longer the methylene chain between neighboring charges on the polymer backbone, the greater is the degree of dissociation, as Manning's theory predicts. The distance between the neighboring charges on the polymer backbone was calculated by using Manning's equation. The distance was compared with that calculated geometrically on the basis of the contour length of the molecule according to Manning's definition. The former distance was much smaller than the latter. The former distance was then compared with the length calculated from Eyring's equation for the end‐to‐end distance of a freely rotating methylene chain. In this case, good agreement was obtained.
Influence of the rotational mobility of probe molecules on their orientation factors
Authors: Hennecke Manfred H.
Published: April 2003

The influence of a small rotational mobility on the measured orientation factors f2 and f4 (connected with the second and fourth moments of the orientation distribution function), of uniaxial probe molecules in uniaxial polymer systems is calculated with special regard to the fluorescence polarization method. A mean angle of rotation of about 10° within the time scale of the experiment, i.e., the fluorescence lifetime, affects f4 considerably, while it has practically no influence on f2. On the other hand, the knowledge of the true f4 of the sample and some assumptions on the mobility—orientation correlation make it possible to evaluate the mean rotational angle θ from the measured f4. Moreover, the measured f2 value can be precisely corrected. The effect of the assumptions on the reliability of f2 and θ is analyzed. Experimental results on two partially mobile probe molecules in drawn polyethylene are discussed.
Structure of the iodine columns in iodinated nylon‐6
Authors: Burzynski Ryszard , Prasad Paras N. , Murthy N. Sanjeeva
Published: April 2003

A study of iodine‐complexed nylon 6 films by polarized resonance Raman spectra shows the presence of both I3− and I5− species, the latter most likely in the form of an I2/I3− complex. Polarization characteristics of the Raman spectra show that the I2/I3 units are orinted along the polymer chain and the I3− ions are perpendicular to the chain axis. The I2/I3− units are in a more stable moiety than the I3− species. These Raman results are consistent with the x‐ray diffraction data.
Diffuse interface between polymers: Structure and kinetics
Authors: Wu Souheng , Chuang Hsiao‐Ken , Han Chang Dae
Published: April 2003

The interfacial structure and diffusion kinetics of two compatible polymers, poly(methyl methacrylate) and poly(vinylidene fluoride) are studied in the melt. The interdiffusion rates of the two components are found to be unequal, giving unequal diffusion coefficients, a net mass flow across the interface, and an asymmetric interfacial composition profile. The structure and kinetics confirm the predictions of the reptation theory. The interfacial thickness d grows with t1/2, and the interdiffusion coefficient is proportional to M−2, where t is the time and M is the molecular weight. The scaling law for the interfacial thickness is therefore d ∝ M−1t1/2. The number of chains per unit area crossing the original interface reaches a constant value independent of diffusion time after a short induction time on the order of the tube disengagement time (about 0.1–10 s in the present cases depending on the molecular weights). The adhesive bond strength σ is scaled by σ ∝ t1/4M−1/2 and σ/σ∞ ∝ t1/4M−1/2 [1‐ (Mc/M)]−1, where σ ∞is the σ at infinite molecular weight and Mc is the entanglement molecular weight.
The relaxation and deformational properties of a carbon‐black filled elastomer in biaxial tension
Authors: Sullivan J. L.
Published: April 2003

Biaxial stress relaxation data acquired for a carbon‐black‐filled elastomer are analyzed. Consistent with previously published simple‐tension and pure‐shear results for this elastomer, the biaxial relaxation behavior is also found to be a separable function of time and strain effects. A departure from separability is observed at the larger strain; this might be a manifestation of strain‐induced crystallization. An analysis of the biaxial results together with the earlier reported simple‐tension and pure‐shear data reveals that the deformational dependence of this elastomer obeys the Valanis—Landel hypothesis up to moderate deformations. The Ogden strain energy function is found to be an excellent analytical representation of all of the multiaxial data. Large relative errors found at small tensile strains between the data and the Ogden fit are attributed to carbon black structural effects.
Rheology of hydroxypropylcellulose solutions
Authors: Navard P. , Haudin J. M.
Published: April 2003

The rheology of hydroxypropylcellulose (HPC)—acetic acid solutions was investigated by using a cone‐and‐plate rheometer and a capillary rheometer, for polymer concentrations ranging from 10 to 80%. Isotropic solutions exhibit a Newtonian plateau followed at higher shear rates by a pseudoplastic zone. The apparent viscosity varies as C5.2 if concentration C is less than 27% and as C13 for 27% < C < 30%. A biphasic interval (isotropic and cholesteric phases) exists between 30 and 35%. A maximum in viscosity is observed at C = 30%, the height of the viscosity peak being a decreasing function of shear rate. Anisotropic solutions are strongly viscoelastic. Both isotropic and anisotropic solutions give results (apparent viscosity, first normal‐stress difference, relaxation time, etc.) which are not in good agreement with Doi's theory. This is understandable since the HPC chain cannot be modeled by a rigid rod. Upon heating, anisotropic HPC—acetic acid solutions undergo an anisotropic to isotropic phase transition which is easily detected by a maximum in the temperature dependence of the first normal‐stress difference and of the apparent viscosity.
The solubility and diffusion of water in poly(aryl‐ether‐ether‐ketone) (PEEK)
Authors: Grayson Michael A. , Wolf Clarence J.
Published: April 2003

The transport properties of water in neat poly(aryl‐ether‐ether‐ketone) (PEEK) coupons (2 to 6 mm thick) were investigated by gravimetric and mass spectrometric methods. The solubility of water increases from 0.44 wt.% at 35°C to 0.55 wt.% at 95°C; the temperature coefficient is 8 kJ/mol (1.9 kcal/mol). The diffusion processes for sorption, desorption, and resorption at 35°, 50°, 65°, 80°, and 95°C are, within experimental error, the same. The activation energy for diffusion is 42.7 kJ/mol (10.2 kcal/mol). The diffusion process is classical Case I Fickian in the temperature region investigated.
Microphase structure of interpenetrating polymeric networks based on polyurethane and polyurethane ionomer
Authors: Lipatov Yu. S. , Shilov V. V. , Bogdanovich V. A. , Karabanova L. V. , Sergeeva L. M.
Published: April 2003

Interpenetrating polymer networks based on polyurethane and polyurethane ionomer were studied using wide‐angle and small‐angle X‐ray diffraction. The polyurethane network is a multiblock polymer based on the trimethylolpropane adduct with 2,4‐toluene‐diisocyanate and poly(propylene oxide tetrahydrofuran) copolymer. Polyurethane ionomer represents a network formed from poly(propylene glycol) containing three OH side groups, 2,4‐toluene‐diisocyanate, 2,2′‐dimethylethanol‐amine, and 1,5‐dibromopentene. The network polymers are characterized by structure heterogeneity developed during microphase separation as a result of hard and soft block segregation. The interpenetrating networks investigated are amorphous systems over the whole range of compositions. They form a very complicated structure where the phase separation of polyurethane and ionomer takes place. It is important to note that phase separation leads to the appearance of microphase structure periodicity due to regular arrangements of microregions enriched by one of the components. The latter fact is considered to be a sign of spinodal phase separation at the initial stages.
Relaxation properties of some segmented polyurethane‐CaCO3 composites. A Dielectric study
Authors: Báanhegyi Gyöurgy , Rho Man‐Khyun , Chien James C. W. , Karasz Frank E.
Published: April 2003

Dielectric relaxation in three segmented polyurethane‐CaCO3 composites was investigated between −70°C and +150°C in the 300 Hz to 100 kHz frequency range. Two of the polymers contained a polyacetal‐polyether soft segment, whereas the soft component of the third polymer was polypropylene oxide. The hard segments consisted of 4,4′‐diphenyl methane diisocyanate in two cases and toluene‐2,4‐diisocyanate in the third case.

In parallel studies two calorimetric relaxations, designated α and α′, were observed for each sample and were determined to be glass transitions of the soft and hard segments, respectively. In general, the transition temperatures decrease with increasing filler content. High frequency, low temperature permittivities increase while low frequency, high temperature AC conductivities generally decrease with increasing filler content. The shift in the transition temperatures can be explained using the adsorption theory of filler‐polymer interactions and the densities of the samples. The interfacial polarization mechanism becomes important only above the α′ transition temperature and below 1 kHz.
On the percolative behavior of carbon black cross‐linked polyethylene systems
Authors: Benguigui L. , Yacubowicz J. , Narkis M.
Published: April 2003

The dielectric properties of peroxide cross‐linked polyethylene–carbon black composite systems are described in the frequency range between 10 and 107 Hz as a function of frequency and carbon black loading. Very high values for the dielectric constant were obtained when measuring conductive samples. A percolative model gives a suitable explanation, within experimental limits of the properties of the systems studied.
A study of aqueous solutions of dextrans by gel permeation chromatography using a multiple detection system
Authors: Van Dijk J. A. P. P. , Varkevisser F. A. , Smit J. A. M.
Published: April 2003

We studied the elution of dextrans in gel permeation chromatography (GPC) using a low‐angle laser light‐scattering (LALLS) system to monitor the molecular weight and the standard refractive index (RI) detector to measure the concentration. In pure water the dextrans show bimodal chromatograms of the RI response as well as of the LALLS response. The first eluted peak reflects the macroion exclusion due to the repulsion between negatively charged macromolecules and equally charged gel. In spite of the resulting distortion of the chromatograms, correct values of the weight‐average molecular weights (M̄w) are obtained from them. If instead of pure water a salt solution (0.1 M KNO3) is used as eluant, the charge effect is completely suppressed and single‐peak chromatograms are found. Again correct values of M̄w are obtained, but number‐average molecular weights turn out to be too large owing to axial column dispersion in the coupling arrangement. By introducing a spreading factor, values of M̄n could be corrected. Investigations of the charge effect were also carried out by monitoring the electric conductivity of the eluted dextran zone. In this way, the phenomenon of ion inclusion, evidently provoked by charged dextran molecules, was observed.
Hydrostatic compression of the monoclinic form of polyethylene
Authors: Miyaji Hideki , Asahi Takanao , Miyamoto Yoshihisa , Asai Kenjiro
Published: April 2003

Lattice constants of the monoclinic form of polyethylene under pressures up to 1.8 GPa at 298 K are investigated by x‐ray diffraction. The thermal expansion from 100 K to 300 K at atmospheric pressure is also studied. The equation of state is calculated by Pastine's method, taking into account the zero‐point vibration, and is compared with experimental results. The calculated results depend largely on the interatomic potential used and the limit of the interatomic distance for summation of the potentials. A change in the angle γ between the a and b axes results in an anisotropic change in the unit cell dimension with both pressure and temperature; the a and b axes change at nearly the same rate. The monoclinic form may have a higher density than the orthorhombic form at pressures above 1.0 GPa.
RHEED investigation of thin tin films on polypropylene
Authors: Schultz J. M. , Peneva S. K.
Published: April 2003

Thin layers of (25–1000 Å) tin were evaporated onto a highly oriented polypropylene sheet. Two rates of deposition were used: 5 and 20 Å/s. For the more rapid deposition rate, a preferred orientation of tin was found in all cases. Here, the Sn a axis lay parallel to the polymer chain (polymer c axis). The same orientation relationship was found for the slower deposition rate, but only at lower Sn film thicknesses; at the higher film thicknesses, a random orientation of crystallites is found. Scanning electron micrographs show an equiaxed tin grain structure for the case of no preferred orientation and a platelet morphology for the case of preferred orientation, the thin dimension of the platelets lying perpendicular to the polymer chain axis. Although no clearcut evidence either for or against crystallographic epitaxy has been found, a plausible case for geometrical epitaxy is presented.
Evolution of structure and properties in fiber formation from a thermoplastic polyester‐polyether segmented copolymer
Authors: Abhiraman A. S. , Kim Y. W. , Wagener K. B.
Published: April 2003

Process‐structure‐property relationships in the formation of an elastic fiber from a melt of segmented polyester‐polyether copolymers are described. The “soft” segment, polyethylene oxide, is modified to prevent its crystallization at use temperatures. Features of the polymer related to phase separation of the soft segments and the crystallizable “hard” segments are discussed. An “ideal” morphology of such a thermoplastic elastomeric fiber that would maximize its recoverable extension is defined, and a path toward its realization in a melt spinning process is described.
Influence of reptation on localized diffusion in crystallizing polymers
Authors: Keith H. D. , Padden F. J.
Published: April 2003

Crystalline texture in polymer spherulites appears to be determined in part by interplay during solidification between interface morphology and the diffusion of species segregated at crystal growth fronts; these species are molecules of lower molecular weight (fractionation) or molecules of stereoirregular structure. Early discussions of this behavior were based upon assumption of a single diffusion coefficient in each case. However, it is now known that, because of reptation, each molecule in a polymer melt diffuses with a diffusion coefficient dependent on its individual molecular weight. In this paper, the influence of reptation upon concentration profiles and diffusion ranges is examined. It is shown that such influence is slight when segregated species have relatively narrow distributions of molecular weight, such as are typical when segregation involves fractionation or is mostly confined to fractionated stereoirregular species blended with crystallizable host polymer. With broad distributions, however, concentration profiles are significantly altered and long segregated molecules dominate morphologically important behavior. Meaningful average diffusion ranges can often be derived and related to appropriately averaged molecular weights of participating molecules. Morphological implications of the various results are outlined.
Theoretical prediction of minima in association constants for complex formation between alkylviologens and indole derivatives in the presence of polyelectrolytes
Authors: Ishiwatari Tsutomu , Yoshida Satoshi , Morita Mariko , Seki Ikuko , Mitsuishi Masaru
Published: April 2003

Association constants K for the complexation between various alkylviologens (methyl, propyl, butyl, pentyl, and hexyl) and indole derivatives (acetate and butyrate) have been determined. The order of K values indicates the important role of hydrophobic interactions in aiding the formation of charge transfer complexes. Influences of two kinds of polyelectrolytes; i.e., potassium polystyrenesulfonate (KPSS, anionic) and 3,3‐ionene (cationic) on the K values were also examined. KPSS decreased the K value but, interestingly, yielded a minimum, and the K value increased at high KPSS concentrations. The influence of the type of alkylviologen on the K versus [KPSS] plots was successfully understood by a theory of substrate partitioning between bulk water and the environment of the polymer.
Tensile stress and recoverable strain measurements on polystyrene melts. Interpretation of results in terms of rubberlike elasticity
Authors: Muller R. , Froelich D. , Zang Y. H.
Published: April 2003

Extensional tests at constant strain rate \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document} have been carried out on polystyrene melts with different molecular weight distributions at various temperatures and strain rates. The true tensile stress is found to be well approximated by the sum of two contributions: (1) a neo‐Hookean expression involving the recoverable strain and (2) a contribution rapidly reaching a steady‐state value. Two experimental parameters can be defined: an elasticity modulus \documentclass{article}\pagestyle{empty}\begin{document}$ G(\dot \varepsilon ) $\end{document} from (1) and a viscosity \documentclass{article}\pagestyle{empty}\begin{document}$ \eta _{\rm v} (\dot \varepsilon ) $\end{document} from (2). It is further shown that time‐temperature equivalence applies not only to the stress but also to the recoverable strain and to G and ηv. The dependence of G and ηv on strain rate is then discussed. For high strain rates, G is close to the linear viscoelastic plateau modulus of PS melts and decreases with decreasing strain rate. The value of ηv is found to a good approximation to be equal to three times the shear viscosity taken at a shear rate equivalent to the elongational strain rate.
Isomorphic behavior of poly(aryl ether ketone) blends
Authors: Harris James E. , Robeson Lloyd M.
Published: April 2003

Blends of various poly(aryl ether ketones) have been found to exhibit a range of miscibility and isomorphic behavior. This range is dependent on molecular weight; however, for poly(aryl ether ketones) with number‐average molecular weight of 20,000, this range is about ±25% difference in ketone content. All miscible blends exhibit isomorphism, and all immiscible blends exhibit no evidence of isomorphism. The dependence of the glass transition temperature Tg versus composition exhibits a minimum deviation from linearity whereas the melting temperature Tm versus composition exhibits a pronounced maximum deviation from linear behavior.

The crystalline melting point versus composition for isomorphic blends is considerably different than for random copolymers with isomorphic units. Homopolymers and random copolymers exhibit a melting point that is a linear function of ketone content (increasing ketone content increases Tm). For blends, the melting point is essentially the same as that of the higher melting constituent until high levels of the lower melting constituent are present. The observed melting point versus composition behavior will be interpreted using classical theory to calculate the components of the liquid and crystalline phase compositions. As a miscible blend is cooled from the melt, essentially pure component of the highest melting point crystallizes out of solution, as predicted by calculated solid‐liquid phase diagrams. This occurs until the crystallization is complete owing to spherulitic impingement. At high concentrations of the lower melting constituent, lower melting points will be observed because the highest melting constituent will be depleted before the crystallization is complete.

In many miscible blends involving addition of an amorphous polymer to a crystalline polymer, the degree of crystallinity of the crystalline polymer has been shown to increase. On the basis of evidence presented here, it is hypothesized that dilution by a miscible, amorphous polymer allows for a higher level of crystallinity.
Interaction parameters of polystyrene‐polyisoprene‐toluene systems at 45°c from gel permeation chromatography
Authors: Tseng Hsiao‐Show , Lloyd Douglas R. , Ward Thomas C.
Published: April 2003

Equilibrium phase diagrams of narrow molecular weight distribution samples of polystyrene and polyisoprene in the presence of toluene at 45°C and 1 atm pressure were established by means of gel permeation chromatography. The polymer‐polymer interaction parameter was evaluated on the basis of the Flory‐Huggins approach. The influence of polymer molecular weight and polymer‐solvent interaction parameters on (i) the shape and location of the binodal curve, (ii) the location of the critical point, and (iii) the polymer‐polymer interaction parameter was investigated.
Moderately concentrated solutions of polystyrene. II. Integrated‐intensity light scattering as a function of concentration, temperature, and molecular weight
Authors: Hager B. L. , Berry G. C. , Tsai H.‐H.
Published: April 2003

Integrated‐intensity light scattering data are reported for moderately concentrated solutions of polystyrene in benzene and in cyclopentane. The benzene system is one for which the second virial coefficient A2 is large; data obtained over the range 0.5 < A2Mc < 30, with c the polymer concentration, are analyzed in terms of the (extrapolated) intensity at zero angle and the angular dependence of the intensity. The former is discussed in terms of power law representations based on scaling relations, which are found to represent the data. The latter is discussed in terms of the dependence of the chain dimensions on concentration. With cyclopentane, the behavior is similar for temperatures for which A2 is near its maximum, but for T near either ΘU or ΘL, for which A2 is zero or small, the angular dependence of the scattering is distinctly different, with the intensity exhibiting a maximum as a function of scattering angle.
Brillouin scattering of oriented films of poly(vinylidene fluoride) and poly(vinylidene fluoride) ‐poly( methyl methacrylate) blends
Authors: Wang C. H. , Liu Q.‐L. , Li B. Y.
Published: April 2003

Temperature dependent Brillouin scattering studies of PVF2 films stretched to various stretch ratios have been carried out. Elastic constants for unstretched and stretched films have been obtained as functions of temperature. The elastic constant C33 of the stretched films has a greater temperature dependence than that of unstretched films. To elucidate the effect of the surrounding amorphous matrix on the Brillouin spectrum of semicrystalline PVF2 film, we carried out Brillouin scattering studies of films made from blends of PVF2 and PMMA.
Crystal structure of nylons 2/3/3 and 1,3
Authors: Puiggalí Jordi , Muñoz‐Guerra Sebastián
Published: April 2003

The crystal structures of two polyamides, poly(glycyl‐β‐alanyl‐β‐alanine) (nylon 2/3/3) and poly(methylene malonamide) (nylon 1,3), have been investigated by x‐ray diffraction and electron microscopy. Crystallization of nylon 2/3/3 from a solution in a mixture of water and formic acid yields lamellar single crystals exhibiting a triangular habit. Doughnut‐shaped morphologies diffracting as single crystals are obtained in the crystallization of nylon 1,3. A helical structure of the type known as polyglycine II is found for both polyamides. In such a structure, chains are intermolecularly linked by hydrogen bonds giving a hexagonal lattice of a = 4.79 Å. Insufficient data are available to determine precisely the conformation of the chains. We assume a threefold helix having c = 35.2 Å and c = 18.0 Å for nylon 2/3/3 and nylon 1,3 respectively. No sign of the layered structure familiar in polyamides has been detected for these polymers throughout the experiments made in the present study.