bluuebunny/crossref_metadata_2025 huggingface dataset:
Properties of amorphous and crystallizable hydrocarbon polymers. II. Rheology of linear and star‐branched polybutadiene
Authors: Rochefort W. E. , Smith G. G. , Rachapudy H. , Raju V. R. , Graessley W. W.
Published: April 2003

Some results are reported on the linear viscoelastic properties of polybutadienes with narrow‐molecular‐weight distributions. The zero shear viscosity η0 varies as M3.4 in the linear samples, and viscosity enhancement is found in star‐branched samples with long arms, in good agreement with results reported earlier by Kraus and Gruver. The temperature coefficient of viscosity appears to be slightly larger in stars when the arms become long. The steady state recoverable compliance J is 2.1 × 10 −7 cm2/dyn in linear samples of high molecular weight, but it increases to values as much as 10 times larger in the stars. The plateau modulus G, obtained from a composite curve for the linear samples, is 1.32 × 107 dyn/cm2. The terminal relaxation spectrum of the stars is too broad to allow an evaluation of plateau modulus.
Properties of amorphous and crystallizable hydrocarbon polymers. III. Studies of the hydrogenation of polybutadiene
Authors: Rachapudy H. , Smith G. G. , Raju V. R. , Graessley W. W.
Published: April 2003

Three methods for hydrogenating anionically prepared polybutadiene (containing about 8% vinyl double bonds) were investigated: homogeneous catalysis (alkylated transition metal salts), heterogeneous catalysis (nickel on kieselguhr; paladium on calcium carbonate), and stoichiometric reaction with in situ generated diimide. The products were characterized by intrinsic viscosity, gel permeation chromatography, infrared spectroscopy, and melt viscosity. Only the heterogeneous catalysts were found to yield completely hydrogenated products without incorporation of foreign groups and without significant change in the large‐scale molecular structure of the chain. The 195°C melt viscosity of linear polybutadiene hydrogenated with heterogeneous catalysts is virtually identical with that of linear polyethylene with the same intrinsic viscosity in trichlorobenzene at 135°C. The solid state properties of hydrogenated polybutadiene, containing about 20 ethyl branches/1000 main chain atoms, closely resemble those of commercial branched polyethylene.
Effect of hydrogen bonding on the anisotropy of the hydrostatic compressibility of polymer crystals
Authors: Ito T. , Hirata T. , Fujita S.
Published: April 2003

Correlations between the crystal structures of polymers consisting of the hydrogen‐bonded molecular sheets and anisotropy of the linear compressibility (K0) of the crystal were studied at 20°C under hydrostatic pressures up to 6 kbar. For nylon‐6, it was found that K0 is more than four times larger in the direction normal to the hydrogen‐bonded sheet than in the parallel direction. The inversion of the sheet direction involved in the α → γ transition of nylon‐6 was clearly reflected in the anisotropy of the linear compressibility. For atactic poly(vinyl alcohol), K0 in the c‐axis direction was 1.6 times larger than that in the a‐axis direction, which is consistent with a structure model with the hydrogen‐bonded sheet parallel to the a‐axis. Theoretical calculations by Tashiro et al. indicate, however, the anisotropy does not necessarily correspond to the sheet structure when the direction of the hydrogen bonds strongly deviates from the plane of the sheet.
The role of inertial effects in macroparticle diffusion
Authors: Altenberger A. R.
Published: April 2003

The influence of macroparticle and solvent inertia on diffusion of interacting spherical Brownian particles is studied. Results are applied to the determination of the spectrum of light and neutrons scattered quasielastically from solutions of macroparticles.
Studies of orientation and structure of crazed matter in polystyrene. II. Electron diffraction measurements
Authors: Brown H. R.
Published: April 2003

The technique of selected area electron diffraction in the transmission electron microscope is used to examine the degree of orientation of crazed matter. The theories of electron and x‐ray diffraction are compared and it is shown experimentally, by comparison with published x‐ray results, that it is possible to obtain electron diffraction patterns from uncrazed polystyrene that are reasonably free of both radiation damage and multiple scattering problems. Electron diffraction patterns from crazes show a considerable degree of orientation but otherwise are very similar to those from uncrazed material, showing that crazes have no structure different from that of bulk material. Diffraction patterns are also obtained from thin films drawn to draw ratios of 4.5 and 6 at 90°C. These agree well with published x‐ray results from oriented polystyrene but show less anisotropy than the craze diffraction patterns.
Hydrogen bonding effects on the skeletal optical and the longitudinal acoustical modes in long chain molecules and polymers
Authors: Rabolt John F.
Published: April 2003

Raman spectra of stearyl alcohol (n‐C18H37OH) indicate that vibrational bands in both the skeletal optical (1000‐1200 cm−1) and longitudinal acoustical (0–500 cm−1) regions are considerably perturbed by intermolecular hydrogen bonding. The zone interior skeletal stretching mode reflecting phonon dispersion in the v4 branch of the infinite polyethylene chain is found at 1105 cm−1, approximately 20 cm−1 higher than in the corresponding n‐alkane. Similarly the single nodal longitudinal acoustical mode (LAM‐1) is found shifted by 12 cm−1 to higher frequency when the expected “mass effect” produced by the OH group is considered. This shift is further increased to 16 cm−1 at −100°C indicating a further perturbation on this accordion mode due to the increased strength of the hydrogen bond at the low temperatures. The positions of the higher multinodal vibrations, LAM‐3 and LAM‐5, are also perturbed by the hydrogen bond but by differing amounts. The observation of a low‐frequency Raman‐active LAM in polytetrahydrofuran [(CH2CH2CH2CH2O)n] is discussed in conjunction with the expected effects of hydrogen bonding at the lamellar surface.
Effect of nonhomogeneous shear rates on the flow‐induced crystallization of flexible macromolecules
Authors: Silebi C. A. , McHugh A. J.
Published: April 2003

Several observations are made regarding the role of nonhomogeneous shearing rates in the process of flow‐induced fibrillar crystallization from solution. The flow geometry chosen in the present analysis is that occurring in the annular region between two concentric cylinders. Computational evaluation and discussion of the effect of stress‐induced diffusion is presented in terms of the elastic dumbbell model. Significant variations in concentrations in the annular region are predicted at full development. Estimates of the dynamics of development of these profiles indicate that the length to capillary radii for full development depends upon the molecular weight of the polymer and the relative dimensions of the concentric cylinders. These results indicate the important role of stress‐induced diffusion in the process of thickening of fibrillar crystals.
Dielectric relaxation in some polyacrylate solutions
Authors: Murthy V. R. K. , Kadaba P. K. , Bhagat P. K.
Published: April 2003

The dielectric constant ϵ′ and loss factor ϵ″ of poly(butyl acrylate), poly(butyl methacrylate), and poly(isobutyl methacrylate) solutions are reported in the frequency region of 1 kHz to 24.42 GHz at four different temperatures of 27, 40, 50, and 60°C. Cole–Cole plots are plotted to obtain the distribution parameter and relaxation time. The activation energies are evaluated assuming dielectric relaxation to be a rate process in these solutions. A possible relaxation mechanism is discussed.
Photon correlation spectroscopy of polystyrene near the glass–rubber relaxation
Authors: Lindsey C. P. , Patterson G. D. , Stevens J. R.
Published: April 2003

Polarized Rayleigh scattering is studied near the glass‐rubber relaxation in atactic polystyrene using photon correlation spectroscopy. Average relaxation times determined from the data agree well with previous results obtained using depolarized Rayleigh scattering. The light scattering results follow the same trend observed by dielectric and mechanical relaxation studies, but the times for orientational relaxation are longer by approximately two orders of magnitude. Also, an extensive discussion of the experimental techniques necessary to use photon correlation spectroscopy of polymers near the glass‐rubber relaxation is presented.
Structure of diepoxide–diamine network polymers. I. Average network properties
Authors: Charlesworth John M.
Published: April 2003

A study of some of the average chemical properties of a variety of diepoxide–diamine network polymers has been carried out. The weight fraction of sol, the quantity of unreacted epoxide in the sol, and the number‐average molecular weight of the sol have been measured for polymers prepared from both stoichiometric and nonstoichiometric ratios of diamine and diepoxide. Theoretical expressions for these quantities have been calculated using the methods recently developed by Macosko and Miller. These relationships were found to give close agreement with the experimental behavior.
Structure of diepoxide–diamine network polymers. II. Soluble chemical species
Authors: Charlesworth John M.
Published: April 2003

Gel permeation chromatography has been used to separate diepoxide–diamine oligomers, produced at a variety of stoichiometric ratios, into individual chemical species. Probability theory has been applied to calculate expressions for the amounts of each of these compounds and close agreement has been found with the experimental results. In conjunction with previous conclusions, this provides compelling evidence in favor of a purely random reaction mechanism, contrary to the inhomogeneous network‐forming mechanism suggested by other workers. The effect of adding an inert diluent prior to reaction has been investigated and it is evident that the fraction of intramolecularly formed bonds increases as the concentration of polymer decreases.
Studies on partially polymerized 2,4‐hexadiyn‐1,6‐bis(p‐toluenesulfonate)
Authors: Patel G. N.
Published: April 2003

An improved procedure for the synthesis of high‐purity 2,4‐hexadiyn‐1,6‐bis(p‐toluenesulfonate) (PTS) is described. The melting point of partially polymerized PTS increases monotonically with increasing polymer conversion (<12%). The increase in melting point is due to formation of a solid solution of unreacted monomer and polymer chains. The relation between the melting point and polymer conversion can be used for determination of polymer conversion. The low‐conversion (<12%) poly PTS is soluble in dimethylformamide. The solution is yellow (λmax ≃ 450 nm) and does not undergo a color change when the temperature is lowered or a nonsolvent is added. Gel permeation chromatography (GPC) studies show that the molecular weight distribution of poly PTS is very broad and does not change with increasing polymer conversion up to <12%. The degree of polymerization for the low‐conversion polyPTS is very low, about 20 repeat units. The G value for initiation centers (radicals) is about 2. The properties of the low‐conversion partially polymerized PTS are compared with the corresponding properties of poly(diacetylene diurethanes).
Rheological study of an aromatic polyamide‐hydrazide
Authors: Baird D. G. , Ciferri A. , Krigbaum W. R. , Salaris F.
Published: April 2003

Rheological and rheo‐optical data are reported for the poly(terephthalamide of p‐aminobenzhydrazide), X‐500, in dimethyl sulfoxide solutions in the concentration range 0.2 to 6.0 g/100 ml. The objective of these measurements is to seek evidence of shear‐induced isotropic → nematic phase transition. Three types of measurement, Couette, cone and plate, and capillary rheometer, all indicate that this system exhibits flow instabilities at high shear rates and concentrations. In this region both the viscosity and the primary normal stress difference decrease with time under shear. In the capillary rheometer the apparent viscosity is smaller for shorter capillaries and, for short capillaries, there is a range of shear rates in which plug flow and a coiled extrudate are observed. These instabilities may arise from the existence of a mixture of isotropic and nematic phases. At lower shear rates, where the flow behavior appears normal, the concentration dependence of the flow birefringence increases at a critical polymer concentration C This value is in reasonable accord with the concentration corresponding to the change of slope of logη (measured at low shear rate) vs. logCp. Both the latter measurements appear to be sensitive to the onset of the phenomenon, which may be due to a shear‐induced transition or the rheological effect of chain entanglements.
Thermal behavior of co[poly(ethylene terephthalate)‐p‐oxybenzoate]
Authors: Lader Harry J. , Krigbaum W. R.
Published: April 2003

In a previous investigation of a co[poly(ethylene terephthalate)‐p‐oxybenzoate] containing 30 mole % oxybenzoate units (referred to as T2/30), Krigbaum and Salaris identified the endotherm at tIII = 244°C as a nematic → isotropic transition. Subsequent investigation revealed that the tIII endotherm disappeared if the polymer is heated to the isotropic melt or dissolved and reprecipitated. The loss of the tIII transition might be due to molecular weight reduction, sequence randomization, or erroneous identification of the transition. Viscosity and high‐field NMR data eliminate the first two explanations. Annealing studies at temperatures higher than those of the earlier work demonstrate that the tIII transition, in fact, represents the melting of crystallites formed during a high‐temperature annealing operation. Moreover, we cannot determine the thermodynamic melting temperature of the copolymer from solid‐state annealing studies. Hence, the principal objective of the study of Krigbaum and Salaris, to compare the enthalpies and entropies of the nematic → isotropic and crystal → isotropic transitions, must be fulfilled in future work.
Statistical mechanical model of diffusion of complex penetrants in polymers. II. Applications
Authors: Pace R. J. , Datyner A.
Published: April 2003

The theory of Part I is applied to the diffusion of several aromatic diffusants in two “smooth chained” polymers: poly(ethylene terephthalate) (PET) and natural rubber. Modifications of the theory necessary to accommodate vinyl polymers are discussed and applied to benzene in PMA and PEA. In all cases the theory agrees satisfactorily with the experimental D(0,T) and D(c,T)/D(0,T) data, and the values of the disposable rg and Δ parameters are of the expected order. The limiting Arrhenius behavior of benzene in natural rubber appears to be correctly predicted. The cell model is definitely more appropriate than the free volume model for the calculation of enfolding chain effects in highly crystalline PET. For the three amorphous polymers the two models give comparable results, the cell model being somewhat superior for natural rubber and PMA.
Diffusion in a multicomponent inhomogeneous system with moving boundaries. I. Swelling at constant volume
Authors: Rudolph F. B.
Published: April 2003

A medium B contains a substance C which can diffuse. This mixture of B and C is brought into contact with a medium A which itself can diffuse into B. Now C diffuses through a swollen layer of A and B into A. The present study examines mathematically this process which, among other things, could serve as a model for migration in a system consisting of plastic packaging (polymer plus an additive) and the contents of the package. It is assumed that medium A (contents) with a constant diffusion coefficient diffuses into medium B (plastics) and that the diffusion of substance C (additive) in the pure B and into A can also be described by constant diffusion coefficients. The diffusion coefficient of substance C in the zone of mixed A and B is taken to be dependent on the concentration of A in B. Partition coefficients are assumed to exist at all interfaces between the media. The general equations of this coupled diffusion process are solved explicitly. The solutions are discussed and illustrated by several special cases. Furthermore, the total amount of C in A is calculated as a function of the diffusion coefficients of the partition coefficients of time, and of the concentration of A in B.
Thermally stimulated discharge currents from polystyrene‐chloranil complex
Authors: Pillai P. K. C. , Rashmi
Published: April 2003

Transitions in a polystyrene‐chloranil molecular complex have been analyzed by thermally stimulated discharge (TSD) current measurements. Peaks have been observed in the current spectra at 79 (α), 128 (ρ), and at 36°C (β). These peaks are attributed to the following mechanisms: the α peak to the randomization of dipoles at the glass–rubber transition, the ρ peak to the release of space charges via long‐range molecular motions at the liquid–liquid transition, and the β peak to the torsional vibrations of the phenyl side group. A high‐temperature treatment is found to narrow the distribution of the α relaxation and removes the ρ peak from the TSD spectrum. Repeated TSD runs on the same sample have been found to generate charges which give a small peak at 141°C. Absorbed water is found to shift the β and α relaxations to 39 and 91°C. Activation energy, relaxation time, and relaxation constant have been calculated for the α relaxation by the method of Bucci et al. The calculated values of activation energies have been compared with those reported in the literature for pure polystyrene.
Diffusion with discontinuous swelling. V. Type II diffusion into sheets and spheres
Authors: Peterlin A.
Published: April 2003

Type II diffusion into uniform spheres (radius R) and sheets (thickness 2l) is calculated under the assumption that the glass‐gel boundary proceeds at a constant velocity v from the surface towards the interior of the sample, that the diffusion coefficient Dg in the glass is constant and that the diffusion coefficient Dr of the rubbery gel is so much higher than vR or vl that practically no sorbate gradient is needed for the transport through the gel of the sorbate. The diffusion process is completed when this boundary reaches the center of the sample. The concentration profile of the sorbate in the glassy matrix in front of the boundary varies with time and velocity v. It does not, however, influence the boundary propagation velocity. Hence the often observed increase of the rate of the weight gain just at the end of the diffusion process is not considered at all. The relative weight gain of the sample W(t)/W∞ as a function of time is the only quantity usually measured. From the ordinate intercept A and the initial slope B of the plot of W(t)/t1/2W∞ vs. t1/2, one can calculate the characteristic transport properties, i.e., the diffusion coefficient Dg of the glass and the velocity v of the glass–gel boundary.
Dielectric properties of oligomers. VII. Low‐molecular‐weight propylene glycols
Authors: Ikada E. , Fukushima H. , Watanabe T.
Published: April 2003

The dielectric properties of low‐molecular‐weight propylene glycols HO[CH(CH3)CH2O]nH (n = 3, 4, 5) were investigated to clarify the effect of chain length on the dielectric properties. The measurement of dielectric constant and dielectric loss was carried out over the frequency range 30 Hz to 30 MHz at temperatures of −20 to −65°C. The static dielectric constants of these glycols are between 10 and 30, slightly smaller than values for the corresponding ethylene glycols of the same degree of polymerization. All of the Cole–Cole arcs, even that for pentapropylene glycol, can be represented by the empirical Davidson–Cole equation. The dielectric properties of homologous propylene glycols are compared with those for the ethylene glycols and are discussed in terms of the effects of chain length and intermolecular hydrogen bonds.
Recoverable compliance of a series of bimodal molecular weight blends of polystyrene
Authors: Orbon Stephen J. , Plazek Donald J.
Published: April 2003

A series of bimodal molecular weight polystyrene blends was prepared. One component had a molecular weight greater than Mc and one less. The recoverable compliances were measured, and the retardation spectra determined via direct inversion. The retardation spectra of the blends are interpreted on the basis of the behavior of the spectra of the components, as a function of composition. It was observed that the low molecular weight component acted as a solvent. The effect of blending on the high molecular weight spectrum was to shift the position of the first peak to longer times and that of the second peak to shorter times. The peak separation was found to be proportional to the 3.4 power of the product of the molecular weight and the volume fraction of the high molecular weight component.
Melting and crystallization of IUPAC low‐density polyethylenes—characterization by differential scanning calorimetry
Authors: Magill J. H. , Peddada S.
Published: April 2003

Melting and crystallization measurements were made on three low‐density polyethylenes claimed to be chemically similar and to have comparable flow behavior, but exhibiting differences in processing and end‐use properties. These IUPAC‐characterized materials were found to possess almost indistinguishable DSC melting curves obtained from the original polymers or for samples isothermally crystallized in this work. However, in isothermal melt crystallization experiments that were made at high sensitivity, readily distinguishable features were found, thus highlighting the DSC procedure as a useful, simple, and valid means of detecting subtle differences in the crystallizability. These differences are more easily revealed in solidification than in melt flow curves and are undoubtedly correlatable with physical processing where crystallization plays a significant role in determining the material end‐product behavior of semicrystalline polymers.
Some remarks on the dynamics of polymer melts
Authors: Daoud M. , De Gennes P. G.
Published: April 2003

Considering one long chain (N monomeric units) in a homodisperse melt of chemically identical, but shorter, “solvent” chains (P monomers per chain), we propose some tentative scaling laws for the self‐diffusion constant D(N) and the relaxation time T(N) of the solute chain. We also discuss the viscosity increment δη due to a small volume fraction Φ of the long chains. We find three regimes of behavior, depending on N and P, and on the distance between entanglement points (assumed smaller than N and P): (A) reptation of the N chain; (B) Stokes–Einstein regime; the solute moves like a usual polymer coil in a viscous fluid of P chains; (C) mixed regime, where D(N) is controlled by reptation, while δη is of type B. Contrary to our earlier belief, we find no significant regime where the process of “tube renewal” could be dominant.
Transport properties in concentrated polymer solutions
Authors: Perico A. , Cuniberti C.
Published: April 2003

Transport properties of polymer solutions at finite concentration are derived in the partial draining case by formulating a static version of the theory given by Freed and Edwards (FE) for unentangled concentrated polymer solution. The method follows the Kirkwood—Riseman theory for infinitely dilute solutions: the dynamics of the polymer are ignored apart from the overall rotation or translation of the chain and the solvent velocity is given by the Navier—Stokes equations perturbed by point friction forces. The concentration dependence of viscosity and translational friction coefficient of finite chains obtained by numerical calculations are compared with the results of the FE closed‐form solution. It is shown that the screening of the hydrodynamic interaction approximately follows Debye‐like behavior in the entire range of concentration. The progressive balancing of the increasing intramolecular hydrodynamic interaction with its reduction due to the screening effects, as the molecular weight increases, is well evidenced by comparing results obtained at constant number concentration for different chain lengths.
Statistical thermodynamics of polymer solutions. VIII. Effect of intermolecular correlations on rayleigh scattering
Authors: Casassa Edward F.
Published: April 2003

The effect of intermolecular correlations on the angular dependence of the intensity of Rayleigh scattering from a dilute solution of a flexible‐chain polymer in a good solvent is studied for an approximate model that retains the random‐flight intramolecular segment‐pair correlation while probabilities of multiple intermolecular contacts are simplified as products of probabilities of single contacts, all conditional on a common “initial” contact. This model, unlike one in which a polymer chain is represented as a spherically symmetrical cloud of segments, gives very little deviation from Zimm's “single‐contact” approximation in light scattering: i.e., the initial concentration dependence of the concentration/intensity ratio is almost the same at all scattering angles. This behavior, which appears to underestimate the intermolecular correlations, can be accounted for by the symmetry of the bimolecular cluster as represented by the model.
Raman spectra of styrene‐sodium methacrylate copolymers—evidence for ion clustering
Authors: Neppel A. , Butler I. S. , Eisenberg A.
Published: April 2003

Raman spectra of a series of styrene‐sodium methacrylate copolymers of varying sodium methacrylate contents have been investigated in the 425–100 cm−1 region. The bands appearing at 254 and 166 cm−1 have been attributed to ion multiplets and clusters, respectively. From an analysis of the intensities of these bands and a comparison of these intensities with those obtained from an analysis of dielectric data, it seems that Raman spectroscopy is a useful method for determining the concentrations of ions in the two different kinds of sites.
Concentration dependence of the viscoelastic properties of polystyrene‐tricresyl phosphate solutions
Authors: Plazek Donald J. , Riande Evaristo , Markovitz Hershel , Raghupathi N.
Published: April 2003

Based on creep and creep‐recovery measurements, the viscoelastic functions [J(t), Jr(t), J′(ω), J″(ω), G′(ω), G″(ω), and L(lnτ)] are presented for solutions of a narrow molecular‐weight‐distribution polystyrene in tri‐m‐tolyl phosphate in the concentration range of 1% to 100% polymer. For concentrations of 25% polymer and above, two maxima are exhibited by the retardation spectrum, L(lnτ). In the neighborhood of each of the maxima the retardation spectra of the more concentrated solutions can be superimposed by translations along both the logL and logτ axes. Reflecting the increasing width of the rubbery plateau with increasing polymer concentration, the dependence of the concentration time‐scale shift factors is greater for the terminal region of response. The response of the solvent is seen at the lower concentrations and it is a less sensitive function of the concentration than that of the polystyrene. This behavior is associated with the previously reported observation of two glass‐transition temperatures in the middle concentration range. For the higher concentrations, both the steady‐state and rubbery‐plateau compliances are inversely proportional to the square of the concentration.
Method for viscosity measurements at high pressure
Authors: Birnboim Meyer H. , Weiss H.
Published: April 2003

The technique of quasielastic light scattering is utilized to determine the viscosity of fluids subjected to large hydrostatic pressures. In this method, a small concentration of insoluble polystyrene spheres of known diameter, 0.109 μm, is added to the fluid. The high‐pressure cell in which the fluid is contained has three optical windows. The laser light scattered from the suspended spheres is analyzed to determine the diffusion coefficient of the spheres. Since, by the Stokes law, the viscosity of the fluid is determined from the measured diffusion coefficient and known particle radius r. A small correction is required for the contraction of the spheres and for refractive‐index change of the water under pressure. Results on the viscosity of water at 25°C up to pressures of 2.5 kbar are reported and compared with published results. This method is applicable to lubricants and polymer solutions where the viscosity is many orders of magnitude greater than that of water.
Unperturbed dimensions of cyclochain polymers
Authors: Pavlova S. A. , Timofeeva G. I. , Ronova I. A. , Pancratova L. A.
Published: April 2003

The conformational parameters of three polyoxadiazoles were calculated by a direct computer simulation assuming free rotation about virtual bonds. The results obtained proved to be close to those derived from viscosity and sedimentation experiments.
Crystallization of polydioxolan. III. Microscopy and dilatometric analysis of the crystallization kinetics
Authors: Archambault Pierre , Prud'Homme Robert E.
Published: April 2003

Crystallization kinetics has been studied for a polydioxolan (PDOL) sample, over a wide temperature range, by dilatometry and microscopy. The dilatometry results can be analyzed using the Avrami equation. At temperatures higher than 22°C, the crystallization data must be analyzed in two steps: the first part of the curve corresponds to PDOL with a very disordered morphology (Phase I) while the second part of the crystallization curve is related to a spherulitic morphology (Phase II). The passage from the low to the high crystallization temperature region is associated with a change in the Avrami exponent from 3 to 4. The crystal surface free‐energy product σσe was found to be 18 × 102 erg2/cm4, very close to that of polyoxymethylene. The crystallization kinetics was studied by microscopy over the temperature range−18 to 35°C. Growth and nucleation rates were recorded. Two phases are found only at temperatures higher than 22°C. The appearance of Phase II is related to a decrease in the growth rate of the sample. From the growth rates, the crystal surface free‐energy product σσe was found equal to 17 × 102 erg2/cm4. The detailed analysis of the crystallization of the two phases reveals a complicated process which can be divided into four different steps: (a) growth of a disordered phase, Phase I; (b) nucleation of a higher birefringence structure; (c) propagation of a high birefringence phase; and (d) spherulitic growth, Phase II. The analysis of PDOL crystallization strongly suggests the presence of a hedrite → oval → spherulite transition: the hedrite formation corresponds to step (a), the oval formation to steps (b) and (c), and the spherulite formation to step (d).
Melt crystallization of polypropylene: Effect of contact with fiber substrates
Authors: Campbell D. , Qayyum M. M.
Published: April 2003

The isothermal crystallization of isotactic polypropylene at different temperatures in the presence of fibrous substrates has been investigated. It is shown that preferential transcrystalline growth occurs at the fiber surface and that changes in nucleation density in the bulk material adjacent to the fibers also occur, the extent of which is dependent on temperature and fiber volume fraction. The effects are discussed in terms of the diffusion of heterogeneities in the bulk due to interaction and the adsorption on the fibers.
Further studies of the preferred chain conformation of crystalline poly(vinylidene chloride)
Authors: Wu M. S. , Painter P. C. , Coleman M. M.
Published: April 2003

The polymer chain conformation of crystalline poly(vinylidene chloride) (PVDC) has been the subject of controversy for the past three decades. In this study, a combination of techniques has been employed in an attempt to elucidate the preferred conformation of PVDC. Conformational models containing two monomers per translational repeat distance have been considered. Calculations of the translational repeat distance and the nonbonded Cl ⃛Cl contact distance between two adjacent CCl2 groups have been performed for each of the models. By comparing these results with those derived from x‐ray analysis and a theoretical estimation of the minimum nonbonded Cl ⃛Cl contact distance, an initial judgment of the structural feasibility of the models has been gained. A symmetry analysis has been performed for each conformational model and theoretical estimations of the polarization and intensity of the CCl and CH stretching vibrations have been obtained. These results have been compared with experimental infrared and Raman spectra. It is concluded that a TXTX′ (where X and X′ are torsional angles of equal value but opposite sign) chain‐conformational model for PVDC is favored.
Normal vibrational analysis of poly(vinylidene chloride)
Authors: Wu M. S. , Painter P. C. , Coleman M. M.
Published: April 2003

Normal coordinate calculations have been performed for poly(vinylidene chloride) employing a TXTX′ conformational model (X and X′ denote torsional angles of equal value but opposite sign). A valence force field previously determined from the model compounds 2,2‐dichloropropane and 2,2‐dichlorobutane was directly transferred to the chain conformation of the polymer. The results are in excellent agreement with the observed vibrational spectra and we have been able to satisfactorily assign all the major normal modes.
Partial molal volumes of polymers in aqueous solutions from partial molal volume group contributions
Authors: Zana R.
Published: April 2003

It is shown that the partial molal volumes (pmv) of the repeat units of nonionic polymers in aqueous solutions calculated from pmv group contributions, obtained from pmv data for small molecules and salts in aqueous solutions, agree in most instances to within ± 1 cm3/mole with the experimental values. The pmv of ionic polymers calculated from pmv group contributions have been found to be always larger than the experimental values. The difference gives a lower bound of the cooperative electrostrictive effect of neighboring charged sites of the polymer chain on surrounding water molecules.
Isotope effect in the diffusion of hydrogen and deuterium in polymers
Authors: Toi Keio , Takeuchi Kazutoshi , Tokuda Taneki
Published: April 2003

Temperature dependences of diffusion and permeation coefficients of hydrogen and deuterium in glassy and rubbery polymer films have been measured. The size of the free volume element in rubbery polymers has been calculated according to the theory of Frisch and Rogers for the quantum isotope effect, but the free volume is too large for precise calculation below the glass‐transition temperature. The cooperative movement of segments is also discussed using the ratio of preexponential factors for diffusion mechanisms above and below the glass‐transition temperature.
Lamellar morphology of polyethylene: Electron microscopy of a melt‐crystallized sharp fraction
Authors: Grubb D. T. , Keller A.
Published: April 2003

The morphology of linear polyethylene of Mw/Mn 1.19 crystallized isothermally from the melt has been investigated. Electron microscopy (EM) of stained thin sections gave exceptionally well‐defined images. There were no qualitative differences between Regime I and Regime II crystallization, but the lamellae grown at lower supercooling were thicker, larger, and had fewer spiral growths per unit area of fold surface. Small‐angle x‐ray scattering indicated a much sharper distribution of lamellar thicknesses than EM and Raman LAM did. This is evidence of the complementary nature of the techniques and not a contradiction. EM also revealed nonrepresentative features in detail. There were extremely thin lamellae formed on cooling, indicating molecular weight segregation even in this fractionated material, and there were extremely thick lamellae, attributed to isothermal thickening. As the representative lamellae are also supposed to have thickened isothermally, this raises the issue of when and how the lamellae which are the primary products of crystallization can be identified.
Thermal expansion of epoxy‐resin/particle composites—a size effect
Authors: De F. F. Pinheiro M. , Rosenberg H. M.
Published: April 2003

The thermal expansion of epoxy‐resin (Epikote 828)/particle composites has been measured in the range 77 to 450 K. The fillers used were Cu spheres (seven sizes from 5 to 150 μm diameter) and glass ballotini spheres (three sizes from 3.5 to 200 μm diameter). The volume concentrations used were 0.3 and 0.5 for Cu and 0.3 for glass. The experiments show that the addition of filler raises the glass transition temperature Tg, especially for fine particles. Below the normal value of Tg the thermal expansion is independent of particle size while above Tg the expansion is considerably smaller for samples containing the smaller particles. The effect is more pronounced for Cu than for glass filler. In addition a rapid heating rate reduces the expansion for specimens containing smaller particles but it does not effect the expansion for those containing large particles. The results, which are discussed in the light of the work of other authors, suggest that the addition of particles increases Tg by changing the nature of the polymer not only immediately at the particle surface but also for a considerable distance into the polymer itself. This probably occurs because the epoxy bonds strongly to the particles and this inhibits segmental rotations of the polymer even at considerable distances from the particle surface.
Effect of hydrolysis and drying on the siloxane bonds of a silane coupling agent deposited on E‐glass fibers
Authors: Ishida Hatsuo , Koenig Jack L.
Published: April 2003

Molecular structural changes of a vinyl functional silane coupling agent on E‐glass fibers, induced during the immersion test in hot water, have been studied using Fourier transform infrared spectroscopy. The amount of the coupling agent on the glass fibers is reduced by hydrolytic degradation. Silanol groups formed by the hydrolysis of the siloxane groups have been detected in the FT‐IR difference spectrum in the range 930–840 cm−1 due to the SiO stretching mode of the SiOH groups. Heat treatment produces partial reformation of the siloxane bonds.
Effects of pressure on the compressibility and crystallization of poly(ethylene terephthalate)
Authors: Wei K. Y. , Cuculo J. A.
Published: April 2003

The effects of pressure on the compressibility and crystallization of poly(ethylene terephthalate) (PET) have been investigated. The Instron capillary rheometer was adapted as a high‐pressure dilatometer to perform experiments up to 40,000 psi. Compressibilities of solid and molten PET were measured. The increases in compressibility with increase in temperature for the solid state are discussed in terms of free‐volume theory. Results obtained for the melt are explained by invoking the second law of thermodynamics and the effect of pressure on the Gibbs free energy. The effects of temperature and compression rate on the pressure of crystallization (Pc) were also studied. As the crystallization temperature was increased from 240 to 286°C, Pc increased by about 16,000 psi. As the compression rate was raised from 1%/min to 8%/min, Pc increased 10,000 psi. At some undetermined compression rate above 8%/min it seemed impossible to induce crystallization in the melt, even with pressures up to 40,000 psi. Analysis of data on the kinetics of crystallization of PET melt under high pressures revealed low Avrami exponents, for which no unequivocal explanation is offered. It is possible, however, that crystallization at high pressure promotes the formation of a morphology made up of a certain percentage of “extended chains.” The alteration in the attendant spatial geometry involved in the crystallization might explain the lower Avrami exponents found. In another set of experiments, crystallization temperatures (Tc) were measured by slowly cooling PET melt under high pressures. As the pressure was raised from 3000 to 15,000 psi, Tc increased from about 246 to 282.5°C. These results are consistent with thermodynamic theory.
Rheology of concentrated solutions of helical polypeptides
Authors: Kiss Gabor , Porter Roger S.
Published: April 2003

Rheological studies were carried out on concentrated m‐cresol solutions of two helical synthetic polypeptides; poly‐γ‐benzyl‐L‐glutamate (PBLG; molecular weight, 150,000) and poly‐ϵ‐carbobenzyloxy‐L‐lysine (PCBZL; molecular weight, 200,000). Steady shear measurements were made over a range of 0.01–16,000 sec−1 to obtain steady shear viscosity and first normal stress difference. Dynamic viscosity and dynamic storage modulus were measured both by oscillatory shear between cone and plate and also by an eccentric rotating disk device over frequency ranges of 0.1–400 and 0.1–63 rad/sec, respectively. The concentration ranges were such that both liquid crystalline and isotropic solutions were investigated. The previously reported observations of an apparent negative first normal stress difference within a defined range of shear rate for liquid crystalline solutions were confirmed for the PBLG and PCBZL solutions. At high shear rates the peaks in plots of steady shear viscosity against concentration were profoundly suppressed but peaks in first normal stress difference versus concentration were not. The observation of liquid crystalline order in PCBZL/m‐cresol solutions at room temperature constitutes evidence that the inverse coil‐helix transition temperature is lower in concentrated solutions than in dilute solutions. The critical concentration for formation of the liquid crystalline phase was higher for PCBZL than for PBLG, despite a higher axial ratio, due to helix flexibility.
Etude diélectrique de trois copolymères ethylène—monoxyde de carbone
Authors: Decossas Françoise , Moliton André , Marchal Eve
Published: April 2003

Dielectric absorption measurements are made on three ethylene‐carbon monoxide copolymers containing 2.3, 8.7, and 18 CO per 1000 CH2 at frequencies ranging from 1 kHz to 1 MHz throughout the 90–373°K temperature range. Mean values of the activation energies of the γ, β, and α relaxations are found to be, respectively, 11.5, 41.5, and 31 kcal/mole from measurements done at fixed frequency by varying the temperature and 27 kcal/mole for the α relaxation as obtained from measurements at steady temperatures with drifting frequencies. The interaction energy of the CH2 unit in the crystalline polyethylene chain with its neighbors is calculated on the basis of the chain rotation model as well as of the rotation‐translation model proposed by Hoffman et al. It seems that their αc models accounting for the molecular origin of the α relaxation have to be rejected. It is further shown that the sharp decrease of permittivity for high temperature (above 330°K at 1 kHz) is only due to the marked decrease of the density of polyethylene with increasing temperature.
Crystallinity of bulk polyacetylene
Authors: Akaishi Tsukasa , Miyasaka Keizo , Ishikawa Kinzo , Shirakawa Hideki , Ikeda Sakuji
Published: April 2003

The fine structure of bulk trans‐polyacetylene (PA) was investigated by x‐ray diffraction. The degree of crystallinity 0.81, determined by Ruland's method, was significantly higher than the value for linear polyethylene. The disorder parameter k was 5, which is much larger than the value for polyethylene. These results led us to propose that PA crystals are more disordered than PE crystals owing to the higher rigidity of PA chains. Small‐angle x‐ray diffraction indicated that the crystal morphology is of the extended‐chain type rather than lamellar. All results obtained in this work showed that the fine structure of PA bulk is such as to facilitate electrical conduction of bulk PA.
Crystallization and morphology of melt‐solidified poly(vinylidene fluoride)
Authors: Lovinger Andrew J.
Published: April 2003

Crystallization of poly(vinylidene fluoride) (PVF2) from the melt yields two types of spherulites. The first consists of large, highly birefringent, and tightly banded spherulites of the α‐form, which are seen at all temperatures. The second type, termed mixed, crystallizes with a newly reported unit cell which appears to be the correct one for γ‐PVF2, but may contain inclusions of a different form (probably α‐PVF2); it is seen only at relatively high temperatures and frequently exhibits irregular or disorganized birefringent and morphological features. In thin films, some mixed spherulites contain regions of single‐crystal‐like aggregates which are grown parallel to the substrate and appear essentially nonbirefringent between crossed polars. Mixed spherulites frequently undergo transformations at their growth fronts leading to initiation of α‐growth. These transformations are associated with the generally higher growth rate of α‐spherulites which may exceed that of their mixed counterparts by almost seven times. However, with increasing temperature this difference in growth rates is progressively reduced and ultimately reversed.
Thermoplastic urethane elastomers. VI. Dilute solution properties in various solvents
Authors: Seefried C. G. , Koleske J. V. , Critchfield F. E. , Pfaffenberger C. R.
Published: April 2003

A thermoplastic urethane elastomer prepared from a polycaprolactone diol, 4,4′‐diphenylmethane diisocyanate, and 1,5‐pentanediol was fractionated and the solution properties of the fractions were characterized in terms of viscosity and sedimentation. Mark‐Houwink relations were established for data obtained at 30° in various solvents:

In dimethylacetamide, tetramethylurea, and N‐methyl pyrrolidone, the value of Kθ increased systematically in the range (1.7 to 2.0) × 10−3. Lower values of Kθ were obtained in dimethylformamide (0.8 × 10−3) and meta‐cresol (0.9 × 10−3). The molecular expansion coefficients in the various solvents were approximated from the experimental viscosity data. Short‐range interactions between the solvent molecules and polymer chains are suggested as possible causes for differences in the hydrodynamic parameters.
Quantitative determination of mesomorphic regions in oriented polymers from wide‐angle X‐ray diffraction
Authors: Lemanska Gizela , Narebska Anna
Published: April 2003

A method for quantitative characterization of the noncrystalline region in poly(ethylene terephthalate) (PET) fibers based on x‐ray wide‐angle diffraction data is elaborated. The procedure consists in a computational resolution of the diffracted intensity into individual peaks for 010, 110, and 100 planes and into isotropic and anisotropic components of diffuse scattering. The results show that the content of mesomorphic regions in the noncrystalline part of PET fibers with draw ratio of λ = 3.0 varies from 12% to 32% depending on the temperature of heat treatment.
Characterization of polyethylene shish‐kebabs by small‐angle X‐ray scattering
Authors: Van Hutten P. F. , Pennings A. J.
Published: April 2003

Small‐angle x‐ray scattering has been used to characterize a variety of polyethylene fibers of the so‐called shish‐kebab type. These fibers are aggregates of elementary fibrils each consisting of a backbone with a lamellar overgrowth. Intense scattering is due to voids between the lamellae giving rise to a “Bragg maximum” reflecting the ordering of lamellae along the backbones. It can be described by rather broad distributions for both the interlamellar spacings and the lamellar thicknesses. This is shown by comparing experimental scattering curves with SAXS patterns calculated on the basis of the theory for one‐dimensional scattering of linearly ordered lamellar systems, using the general paracrystalline model. A negative exponential distribution for the center‐to‐center distance of the lamellae, characteristic of a random nucleation process, apparently cannot be employed for the description of these shish‐kebab morphologies. From a discussion on the discrepancies between experimental and theoretical scattering curves it is concluded that the fibers may be inhomogeneous with respect to the statistics of lamellar ordering. This may be due to the nonisothermal character of the crystallization process.