摘要:

AbstractRaman spectroscopy, x‐ray diffraction, and thermal analysis are used to investigate the structure of linear high‐density polyethylene rapidly quenched from the melt to cryogenic temperatures. All the results point to the production of a glassy phase which crystallizes when heated above 17

ISSN:0098-1273    

DOI:10.1002/pol.1979.180170601

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractLight scattering from concentrated solutions of cellulose acetate in acetone is discussed in terms of exponential correlation functions for refractive‐index fluctuations. These are related to intermolecular aggregation. Light scattering, tensile creep and recovery, and hyperfiltration studies with films of cellulose acetate cast from acetone are discussed in terms of the state of aggregation in the films. It is concluded that intermolecular aggregates are probably small and imperfectly formed regions of microcrystallinity stable up to about 210°C, with the overall state one of near amorphous disord

ISSN:0098-1273    

DOI:10.1002/pol.1979.180170602

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractThe influence of polymer‐polymer interactions and ultrasonic parameters on the ultrasonic degradation of polycaproamide in aqueous 40% H2SO4was investigated. It was found that the rate data for the concentrations studied could be represented well by Ovenall's rate equation. However values of the rate constant chosen to fit Ovenall's equation tend to decrease with increasing concentration of polycaproamide from 0.5 to 2.0 g/100 cm3. With increasing ultrasonic power, the degradation rate increases, but it decreases as frequency is increased. This suggests that cavitation has a dominant rol

ISSN:0098-1273    

DOI:10.1002/pol.1979.180170603

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractInteraction of nonidentical polymer molecules in a dilute solution of a mixture of two polymers is quantitatively characterized byA24, the second virial coefficient for interaction of unlike species. This parameter is related to the compatibility of the two polymers in solution and is obtainable experimentally, e.g., by light scattering. With chemically markedly different polymers,A24depends neither on the molecular weight of the polymers nor on the solvent and becomes characteristic of the polymer pair. For a mixture of two copolymers or of a homopolymer and a copolymer with similar compositions,A24depends both on the solvent and on the molecular weight of polymers. Under such circumstancesA24ceases to be a quantity given only by the chemical structure of the two polymers; however, under suitable conditions it remains a sensitive function of the difference between the chemical nature of polymer components.

ISSN:0098-1273    

DOI:10.1002/pol.1979.180170604

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractComputer modelling studies of the progress of crystallization in polymer melts have been carried out initially on those systems analyzed by Avrami and then extended to include a number of complications which may be characteristic of real systems, in particular (a) mixed mechanism, (b) volume shrinkage, (c) variable crystalline density, and (d) nonrandom nucleation. It is concluded that the Avrami equation is a reasonable approximation to most of these systems except (c).

ISSN:0098-1273    

DOI:10.1002/pol.1979.180170605

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractPolystyrenes, both linear and crosslinked with various crosslink densities, having modified end‐group structures, were synthesized with the objective of studying chain‐end mobility in the glassy state. One end of each polymer chain of these polystyrenes was modified with a fluorescent molecule. These polymers containing fluorescent probes in specific environments have been used in studies of segmental motion using fluorescence depolarization. The mobility has been studied below the glass‐transition temperature as a function of temperature and crosslink density. The experimental data show that chain‐end mobility is not of major importance in connection with the β‐

ISSN:0098-1273    

DOI:10.1002/pol.1979.180170606

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractThe shear‐dependent complex viscosity η*12, which governs the linear time‐dependent stresses in a viscoelastic fluid undergoing infinitesimal shearing oscillations in‐line with a viscometric motion, has been investigated. Formulas relating η*12to measured quantities have been derived for the cone‐and‐plate and parallel‐plate geometries. In the former case, the formula has the same form as that found when there is no steady shearing present. For the parallel‐plate geometry, the formula is different because of the radial variation in the viscometric shear rate. In order to determine the empirical significance of this formula, η*12data were obtained for two fluids, NBS nonlinear sample No. 1 and a 4.3 g/dl aqueous polyethylene oxide (molecular weight, 5 X 106) solution using a Weissenberg rheogoniometer Model R‐18. Data were acquired and analyzed using a minicomputer on‐line with the rheogoniometer. The obtained data indicate that good agreement between the η*12measured using the two geometries is obtained only if the derived formulas are used. Also, it is shown that theoretical results of simple‐fluid theory a

ISSN:0098-1273    

DOI:10.1002/pol.1979.180170607

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractThe variety of wide‐angle x‐ray scattering (WAXS) patterns exhibited by nylon‐6 fibers with different fabrication histories is rationalized using a model comprising three limiting structures, viz., an α, a γ, and a pleated α structure. The γ and pleated α structures both have a single broad reflection in the range 2θ = 19° −25°, but differ in their annealing behavior. At 205° (in vacuo), the pleated α structure converts to the normal α structure by removal of the pleats, without breaking any hydrogen bonds. The γ structure, however, remains unchanged under this annealing condition since it is necessary to break all the hydrogen bonding in the structure to convert it to the α form. Different fabrication routes produce fibers which resemble the three ideal structures to varying extents. Fibers extruded at low speeds (and hence low spinline tension) resemble a mixed conventional α/pleated α structure with only a small γ component. Increasing the take‐up speed (and hence the spinline tension) of the as‐spun fiber, or in‐line drawing of the low orientation fiber (without prior storage), increases the γ content. If drawing of the low orientation fiber takes place after several hours storage (off‐line drawing), a largely α structure is produced. The intensity of the 020 reflection in the γ structure is shown to be very dependent on the degree of cry

ISSN:0098-1273    

DOI:10.1002/pol.1979.180170608

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractIn analyzing the shapes of diffraction peaks from polymers, it has been mistakenly assumed that it is possible to distinguish between models based on “microstrains” and on paracrystallinity. It is shown that either paracrystallinity or distortions due to dislocations give rise to disorder of the second kind andcannotbe distinguished by current diffraction methods. Fourier analysis of shapes of peaks from polymers gives quite satisfactory results, despite comments in the literature to the contrary. The analysis can now be carried out with single peaks; multiple orders are not requi

ISSN:0098-1273    

DOI:10.1002/pol.1979.180170609

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY

摘要:

AbstractThe melting behavior of continuous fibrillar crystals of high‐molecular‐weight polyethylene has been investigated. The macrofibers were grown from dilute solutions in xylene subjected to Couette flow in the temperature range between 103 and 118.5°C. The thermograms, as determined by differential scanning calorimetry, exhibit three melting endotherms with peak temperatures at 141, 150.5, and 159.5°C after extrapolation to zero scan speed. All peaks were found to be strongly superheatable. Reduction of fiber length, in particular by etching with fuming nitric acid, led to the disappearance of the melting peaks at 150.5 and 159.5°C. The remaining peak at 136°C appeared not to be superheatable. The heat of fusion of the fragmented fibers was 69.8 cal/g. Wide‐angle x‐ray diffractograms taken on a macrofiber while gradually heated at a rate of 0.35°C/min at constant length showed that the triclinic phase present in the fiber disappeared at 130°C and that the orthorhombic cell transformed into the hexagonal modification at 150°C. This hexagonal phase was still observable at 180°C. The retractive force developed on heating at constant length displays first a slight decrease followed by a maximum at 150°C. Beyond the latter temperature the stress decays abruptly corresponding to the temperature at which fracture of the fiber could be observed visually. From all these observations it is inferred that the first melting endotherm in the differential scanning calorimeter (DSC) thermograms arises from the melting of unconstrained fibrillar crystal regions which are able to shrink during fusion. Moreover, the melting of lamellar overgrowths on the elementary fibrils on shish‐kebab type may contribute to this endotherm. The second melting endotherm at about 150°C is associated with the transformation of the orthorhombic into the hexagonal lattice in constrained parts of the sample. This latter “rotator” phase allows slippage of the polymer chains past each other, giving rise to stress relaxation. The third endotherm arises from melting of this hexagonal phase and the heat take‐up connected with the formation of higher energygauchestates upon randomization of the chains in the melt. Almost smooth, fully constrained fibrillar crystals grown at high temperature absorb more than 15.5 cal/g during this process, indicating that the polymer chains in such fiber

ISSN:0098-1273    

DOI:10.1002/pol.1979.180170610

出版商:John Wiley&Sons, Inc.    

年代:1979

数据来源: WILEY