bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of molecular weight on the growth rates of low melting spherulites of trans‐1,4‐polyisoprene
Authors: Lovering Edward G. 
Published: April 2003

AbstractGrowth rates of G of low‐melting spherulites in fractions of trans‐1,4‐polyisoprene have been measured. The data were analyzed by use of an equation, ln G = ln G0 − ΔF*/RTc, valid at temperatures close to the equilibrium melting point. Plots of ln G against a function of the critical free energy of nucleation ΔF* result in a family of straight lines having a common intercept, ln G0, which is independent of molecular weight. The slope of these lines is a measure of the interfacial free energy of the crystallites and increases with the molecular weight, reflecting increasing irregularity in the structure of the semicrystalline mass. Comparison of growth rates of low‐melting and high‐melting trans‐1,4‐polyisoprene indicates that G0 does not, to a first approximation, depend on the nature of the crystals growing from the melt. The temperature at which spherulites of the two crystalline forms grow at equal rates has been calculated.
NMR study of molecular motion in oriented long‐chain alkanes. III. Oriented n‐C32H66
Authors: Olf H. G. , Peterlin A. 
Published: April 2003

AbstractThe NMR second moment of a uniaxially oriented mat of single crystals of n‐C32H66 (in the orthorhombic form) was measured at temperatures from −170°C to 70°C and at various alignment angles γ between the orientation axis (preferential direction of the molecular chains) and the NMR magnetic field. Accurate expressions are given for the NMR second moment of an orthorhombic normal paraffin CnH2n+2 of arbitrary molecular chain length n for n ≥ 10, in the following states of molecular motion: no motion (a rigid lattice), rotation of CH3 groups, and rotation of the chains around their axes with superimposed rotation of CH3 groups. In addition to these well‐known motions, n‐C32H66 is found to exhibit an α process. The corresponding decrease of the NMR second moment shows the dependence on γ predicted for “flip‐flop” motion, i.e., rotational jumps of the chain molecules around their axes through 180° and a simultaneous translation along these axes by one CH2 group. The overall decrease in second moment occuring at the transition to the hexagonal rotator phase in n‐C32H66 can be quantitatively accounted for. The dependence of this decrease on the alignment angle γ, however, is in disagreement with calculations based on a simple rotation of the chains around their axes. Considerable torsion of the chains superimposed on the rotation would improve agreement between theory and experiment.
Viscoelastic behavior of polyvinylcyclohexane
Authors: Kelchner R. E. , Aklonis J. J. 
Published: April 2003

AbstractThe tensile stress relaxation master curve for polyvinylcyclohexane (completely hydrogenated polystyrene) has been measured. Direct relaxation experiments were carried out at several temperatures above the glass transition temperature over the rather long time range of four orders of magnitude. This long time span was realized by calculating the modulus during the period when a constant small strain rate was applied to the sample as well as during the usual constant strain interval. A computer solution to the Boltzmann superposition equation allowed data from these two regions to be joined into a smooth curve representing E(t), a parameter indicative of an instantaneous strain experiment. The measured Ti was found to be 143°C; Tg is expected to fall within several degrees of this temperature. This result is apparently at odds with a previously reported Tg value of 120°C. More importantly, the maximum value of the negative slope of the stress relaxation master curve of polyvinylcyclohexane in the primary transition region was only slightly different from that for polystyrene. This observation clearly indicates that the molecular factors which result in the highly coupled nature of the primary transition in polystyrene are not strongly dependent upon any side‐chain π–π interactions which might be present in polystyrene.
Determination of thermodynamic parameters of polymer–solvent systems from sedimentation–diffusion equilibrium in the ultracentrifuge
Authors: Scholte Th. G. 
Published: April 2003

AbstractSedimentation equilibrium in the ultracentrifuge means that there is such a distribution of molecular species throughout the cell, that the centrifugal forces are balanced by differences in the activities. This provides a method for determination of the activities and the chemical potentials in polymer solutions which, in principle, is very simple and reliable. A complication is caused by polydispersity of the dissolved polymer. If one assumes that the interaction parameter depends on concentration and temperature, but not on molecular weight, it is possible to determine the chemical potential of polymer and solvent from the ultracentrifugal data. Experiments have been carried out on the systems polystyrene–toluene and polystyrene–cyclohexane at different temperatures and in the concentration range 0–80 wt‐%. The results are expressed in the data for the chemical potential of the solvent, the number average chemical potential of the polymer and the interaction parameter χ.
Unperturbed dimensions of poly(2‐methyl‐6‐phenyl‐1,4‐phenylene oxide) and poly(2,6‐diphenyl‐1,4‐phenylene oxide) chains
Authors: Shultz A. R. 
Published: April 2003

AbstractThe unperturbed chain dimensions of unfractionated poly(2‐methyl‐6‐phenyl‐1,4‐phenylene oxide) and poly‐(2,6‐diphenyl‐1,4‐phenylene oxide) have been measured by combining molecular weight data from light scattering with intrinsic viscosity data in chloroform. The unperturbed chain dimensions of the former polymer were also measured directly by light scattering dissymmetry in a critical consolute solvent mixture (methyl cyclohexane: 1,4‐dioxane 50:50 by volume). The results of these measurements and of measurements reported by other investigators are satisfactorily explained by postulating no dimension‐expanding prejudice in azimuthal angle in chain conformers of the 2,6‐substituted‐1,4‐phenylene oxide polymers. This corresponds to equal population of the two chain rotation energy minima at azimuthal angles 90° and 270°. Accepting this postulate, one calculates from the observed chain dimensions that the COC bond angle is 118–120° in these aromatic polyethers in solution.
Yield condition and propagation of Lüders' lines in tension–torsion experiments on poly(vinyl chloride)
Authors: Bauwens J. C. 
Published: April 2003

AbstractWe have derived from the Eyring theory of non‐Newtonian flow a yield condition which is valid for an arbitrary state of stress. Experimental data obtained in simple axial compression tests show the influence of the hydrostatic stress on the yielding of poly(vinyl chloride). This fact confirms the proposed condition and disproves the von Mises criterion. Tension–torsion tests performed on thin tubes lead to results which fit our condition fairly well. The pattern of Lüders' lines appearing on the surface of thin tubes subjected to simple tension, simple shear, and tension–torsion are parallel to the direction where the value of the normal stress is equal to the hydrostatic stress.
Wide‐line proton magnetic resonance spectra of some celluloses
Authors: Pittman Robert A. , Tripp Verne W. 
Published: April 2003

AbstractCharacteristic wide‐line proton magnetic resonance absorption spectra of a number of representative cellulose preparations have been obtained in the dry state and after addition of about 7% water. Line widths, second moments, spin‐spin and spin‐lattice relaxation times have been determined. The second moment of the absorption curve of dry cellulose was found to correlate well with the crystalline fraction for most specimens. A technique is described for determining the number of water‐cellulose protons exchanging relative to the number of cellulose protons not exchanging. The reduction in absorption line width observed when water is added to cellulose is shown to be quantitatively consistent with such a proton exchange phenomenon.
Measurements of the relaxation spectra of unplasticized poly(vinyl chloride) melts
Authors: Horsma D. A. 
Published: April 2003

AbstractWe have measured the relaxation modulus in the temperature range 150–220°C of two samples of poly(vinyl chloride) resin with different molecular weights. The data were treated by the principle of reduced variables to yield composite curves. The shift factors (aT) when plotted against reciprocal temperature gave good straight lines from which apparent activation energies were obtained. An apparent activation energy of 50 kcal/mole was obtained for both samples. A relaxation spectrum for each resin was calculated from the relaxation modulus data. These spectra showed a marked molecular weight dependence. The spectra were in the range characteristic of the terminal zone of the entanglement plateau. Zero‐shear‐rate viscosities were obtained from the integration of relaxation modulus plots. From extrapolation of capillary viscosity data it is shown that the viscosity of the higher molecular weight resin used in this study does not approach its zero‐shear value until shear rates less than 10−3 sec−1 are reached. The effect of supermolecular flow units is briefly discussed.
Diffusion of radioactively tagged 1,1‐diphenylethane and n‐hexadecane through rubbery polymers: Dependence on temperature and dilution with solvent
Authors: Wong Chiu‐Ping , Schrag John L. , Ferry John D. 
Published: April 2003

AbstractThe diffusion of 1,1‐diphenylethane in trace amounts through eight rubbery polymers has been studied by radioactive tagging of this penetrant with 14C. For several polymers, the dependence on temperature and on dilution (swelling) by untagged diphenylethane was investigated. In the diluted systems, tagged n‐hexadecane was also used as a trace penetrant. The temperature and concentration dependences were interpreted rather successfully in terms of the free volume. In comparing different polymers, with a 4000‐fold range of diffusion coefficients, the translatory friction coefficient of 1,1‐diphenylethane was found to be proportional to that of n‐hexadecane to the power 1.06. This is interpreted qualitatively by the free volume concept to indicate a slightly less efficient mobility mechanism for the diphenylethane.
On the determination of molecular weight distributions from sedimentation–diffusion equilibrium data at a single rotor speed
Authors: Lee D. A. 
Published: April 2003

AbstractThe problem of inferring molecular weight distributions from concentration gradient data taken at sedimentation‐diffusion equilibrium for a single rotor speed is ill posed: significantly different distributions correspond to concentration gradients which differ so slightly that they cannot be distinguished by the experiment. It is this intrinsic property of the problem which accounts for the lack of success of the several schemes proposed for its solution. Integral equation theory is applied to show explicitly just what can be inferred with bounded error. Several methods for recovering this information are discussed and applied to example problems.
Comonomer and stereosequence distributions in high polymers
Authors: Pyun Chong Wha 
Published: April 2003

AbstractComonomer and stereosequence distributions in linear high polymers are considered from the point of view of the general theory of stationary random sequences. Although the discussion is centered about binary polymerizations which may be regarded as stationary Markov processes of low order, attention is paid to distinguish results valid for any stationary random process including stationary non‐Markov processes from those special to a particular Markov process. Alternative derivations of copolymer composition equations are given along with a corrected version of a previously suggested scheme of relating conditional probabilities of different orders. The nature and relative merits of the several measures proposed in the literature to characterize comonomer and stereosequence distributions are also discussed in some detail.
Dynamic mechanical relaxation effects in some poly(arylene sulfones)
Authors: Kurz James E. , Woodbrey James C. , Ohta Masao 
Published: April 2003

AbstractPoly‐4,4′‐oxydiphenylenesulfonyl and poly‐4,4′‐methylenediphenylenesulfonyl were synthesized by an electrophilic substitution polymerization of the arylene monosulfonyl chloride monomers. The glass‐transition temperatures Tg of these polymers were determined by calorimetric and dynamic mechanical measurements, and the number‐average molecular weights were determined by vapor‐pressure osmometry. Both polymers were found to have the same Tg at equivalent molecular weight; the limiting value at high molecular weight is 238°C. Both polymers have two dynamic mechanical relaxation peaks at temperatures far below Tg. One is in the neighborhood of 0°C, and the other is at −110°C. Plausible origins for these relaxations, and the absence of any near 0°C in poly(4,4′‐isopropylidenediphenylene‐co‐4,4′‐sulfonyldiphenylene dioxide), are discussed.
Polymer characterization by coupling gel‐permeation chromatography and automatic viscometry
Authors: Goedhart D. , Opschoor A. 
Published: April 2003

AbstractA method is proposed for use of the universal calibration curve, i.e., the product of molecular weight and intrinsic viscosity versus retention volume, in calculating the molecular weight distribution of a polymer from gel‐permeation chromatography (GPC) when the Mark‐Houwink relation of the polymer in the solvent used for the GPC is unknown. This is achieved by measuring the viscosity of each fraction with an automatic capillary tube viscometer. Application of this technique to poly(vinyl chloride) and poly(vinyl acetate) proved to be successful.
Viscoelastic behavior of an amorphous polymer under oscillations of large amplitude
Authors: Vinogradov G. V. , Yanovsky Yu. , Isayev A. I. 
Published: April 2003

AbstractThe influence of periodic shear deformation and steady flow on a typical amorphous polymer is discussed. Forced sinusoidal vibrations were applied and the complex viscosity was determined. The action of a vibration of finite amplitude is equivalent to steady flow with a definite finite shear rate. Both processes cause truncation of the long‐time part of the relaxation specturm. It may be accepted to a first approximation that the long‐time boundary of the remaining part of the relaxation spectrum conforms to the long‐time part of the initial spectrum, even if the plateau region of the spectrum is truncated. The concept of limiting truncation of the short‐time part of the spectrum is introduced, this corresponding to the minimum absolute value of the complex viscosity versus reduced frequency and the lowest values of the dynamic and apparent viscosities. With an approximate representation of the relaxation spectrum, calculations were made of the maximum values of the viscosity and the coefficient relating the first difference of normal stresses to the square of the shear rate, and also of the apparent viscosity and normal stresses as functions of the shear rate. The calculated values are compared with experimental measurements, and it is shown that the correlation of the apparent viscosity and the absolute value of the complex viscosity is distributed at high frequencies, being superseded by a correlation between the apparent and dynamic viscosities.
Determination of polymer branching with gel‐permeation chromatography. II. Experimental results for polyethylene
Authors: Drott E. E. , Mendelson R. A. 
Published: April 2003

AbstractThe recently developed methods of characterizing branching in polymers from gelpermeation chromatography and intrinsic viscosity data are verified experimentally. An iterative computer program was written to calculate the degree of branching in whole polymers. Long‐chain branching in several low‐density polyethylene samples was determined by both the fraction and whole polymer methods. The two methods gave consistent ranking of the branching in the samples although absolute branching indices differed. Effects of various experimental errors and the particular model used for branching were investigated. For polyethylene, the data show that the effect of branching on intrinsic viscosity is best described by the relation 〈g3〉W1/2 = [η]br/[η]1 where 〈g3〉w is the weight‐average ratio of mean‐square molecular radii of gyration of linear and trifunctionally branched polymers of the same weight‐average molecular weight.
Heats and entropies of fusion of linear aliphatic polyesters. I. Experimental determinations
Authors: Hobbs Stanley Y. , Billmeyer Fred W. 
Published: April 2003

AbstractPoly(ethylene adipate), poly(ethylene suberate), and poly(ethylene sebacate) were synthesized by a modified ester interchange procedure. Polydispersity was reduced and low molecular weight material removed by fractional crystallization. Samples of 50–60% crystallinity were prepared by bulk crystallization and annealing. Melting points and amorphous densities were obtained by dilatometry. Melting points were 7–12°C higher than previously reported. Heats of fusion were measured by differential scanning calorimetry and extrapolated to 100% crystallinity by using measured amorphous densities and recently redetermined crystalline densities. Entropies of fusion were calculated and separated for the first time into volume expansion and conformational contributions.
Heats and entropies of fusion of linear aliphatic polyesters. II. Molecular origins
Authors: Hobbs Stanley Y. , Billmeyer Fred W. 
Published: April 2003

AbstractThe conformational contribution to the entropy of fusion was calculated for poly(ethylene adipate), poly(ethylene suberate), and poly(ethylene sebacate) from consideration of rotational potentials and steric interactions in model systems. An enumeration scheme similar to that applied to polyethylene was used. Comparison of the observed and calculated conformational entropies indicated the importance of a high‐energy chain twist in the crystalline polyesters in reducing their measured conformational entropies. The rigidity of the polyester chains in the melt is discussed in comparison to polyethylene. The contribution of the polar ester groups to the heats of fusion of the polyesters is evaluated semiempirically.
Thickness of the interphase layer determined from volume changes produced by mutual diffusion in binary microheterogeneous polymer mixtures
Authors: Letz Ján 
Published: April 2003

AbstractThe mutual diffusion of pairs of polymers has been studied at 160°C for two systems: isotactic polypropylene with polyethylene and poly(vinyl chloride) with polyethylene. From the assumption that Fick's law is valid and with a rhombohedral lattice model for the microheterogeneous system, it was possible to obtain from volume changes the thickness of the interphase layer after various diffusion times. It was found that the values so calculated differ considerably from the experimental values, the greatest deviations occuring after 20 min diffusion. From this it follows that non‐Fickian diffusion strongly influences the distribution of concentrations in the diffuse interface, and thus affects the calculated value of the interphase layer thickness. For both polymer pairs Fickian behavior was confirmed for up to about 10 min diffusion time, in good agreement with experimental data.
Size distribution analysis of polymer latex systems by use of extrema in the angular scattering intensity
Authors: Wallace Thomas P. , Kratohvil Josip P. 
Published: April 2003

AbstractThe angular position of the extrema of the vertically polarized scattering intensity has previously been utilized for a method of particle size analysis for systems of monodisperse, spherical, isotropic particles which conform to the Rayleigh‐Gans‐Debye theory. The consequences of a finite polydispersity, which is always present in real systems, was not assessed and the application of the method has resulted in erroneous characterization of some latex systems. This work is concerned with (1) reporting the effects of finite polydispersity on the method of analysis, (2) pointing out previous misuse of the method, and (3) introducing a method of analysis which is based on the position of the extrema but which also considers polydispersity and the exact Mie calculation. This method enables one to characterize a scattering system in terms of a modal diameter and a distribution‐width parameter by utilizing prepared diagrams for a particular relative refractive index.
Self‐seeded crystallization and its potential for molecular weight characterization. I. Experiments on broad distributions
Authors: Keller A. , Willmouth F. M. 
Published: April 2003

AbstractThe effect of varying molecular weight distribution on the self‐seeding phenomenon was investigated by using high molecular weight polyethylene fractions prepared by the stirring‐induced crystallization method of Pennings. The numbers of self‐seeding nuclei per gram were determined by measuring crystal dimensions, and were found to increase with increasing molecular weight of the polymer, in accord with previous findings. In another experiment, self‐seeded single crystals were grown from materials of various molecular weights, prepared by blending two samples of differing molecular weight in various proportions. The concentration of nuclei varies linearly with the weight fraction of high molecular weight polymer in the mixture. This result is shown to be consistent with the proposition that each nucleus contains on the average an identical number (most plausibly one) of molecules of very high molecular weight. The application of this finding to the determination of molecular weights is discussed, and it is shown that the technique provides a method of unprecedented sensitivity for the characterization of the very high end of the molecular weight spectrum. Some morphological results are also presented. In particular, direct observations of the nuclei were found to be consistent with the loosely connected multiple nucleus structure, which had been proposed previously to account for certain light‐scattering results.
Surface crystallization of polypropylene
Authors: Fitchmun D. R. , Newman S. 
Published: April 2003

AbstractCrystallization of compression‐molded isotactic polypropylene and polyethylene is invariably spherulitic; generally, nucleation occurs randomly throughout the sample. In a special case where nucleation predominates at the surface, spherulitic growth centers become crowded and are forced to propagate unidirectionally into the bulk (transcrystallinity). Conditions for the formation of transcrystallinity have been investigated by optical and scanning electron microscopy. The occurrence of transcrystallinity is attributed to heterogeneous nucleation induced at the mold surface. To be effective, the mold surface must have a nucleating efficiency equal to or greater than that of adventitious nuclei present in the polymer. As the crystallization temperature approaches the melting point, the activity of mold surfaces is found to increase leading invariably to transcrystalline formation. The degree of activity of various mold surfaces correlates with the known activity of specific dispersed nucleating agents having similar chemical structures. Contrary to claims in the literature, the surface energy of the mold surface and temperature gradients across the melt surface do not play a primary role in transcrystalline formation of polypropylene.