摘要:

AbstractUltra‐oriented polyethylene fibers obtained by drawing to approximately 30 times their original length have a Young's modulus of approximately 800 kbar. Such fibers, if unconstrained, contract on heating to a length near the original. We have studied the forces causing this contractile behavior by monitoring the stress in the fiber while maintaining it at constant length. In the course of this we observed a complex sequence of both reversible and irreversible behavior. In the reversible case we observed first energy and then entropy elastic behavior. The most significant feature observed is that at sufficiently high temperature the fiber stress relaxes to an unmeasurably low value. A fiber allowed to relax in this way possesses a much lower room temperature tensile modulus (ca. 80 kbar) immediately after relaxation but, remarkably, this modulus increases to approach the initial high value over a period of a few hours when the fiber is stored either clamped or unclamped at room temperature. High x‐ray orientation is preserved throughout the storage period but the density which dropped during the stress decay rose again in the course of the spontaneous stiffening. None of the stress relaxed fibers displays large‐scale contractile behavior on subsequent heating.A phenomenological composite model is proposed which involves stiff microfibrils of short length—surrounded by a matrix present as a minority component. The softening of this matrix on heating and its subsequent stiffening on storage, involving a certain amount of melting and recrystallization, respectively, could then be responsible for the observed variations in the macroscopic tensile properties using simple fiber composite theories. The fibers are likely to be of extended‐chain type produced by the initial drawing while the matrix may consist of a combination of oriented amorphous material (tie chains), randomly oriented chains, and transverse lamellar overgrowth present in varying proportions in the different stages of sample treatment. The wider implications, fundamental and practical, of this remarkable self‐hardening process ar

ISSN:0098-1273    

DOI:10.1002/pol.1977.180150301

出版商:John Wiley&Sons, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractThe free‐volume theory describing diffusion in polymer–solvent systems is reexamined. Calculation of the specific free volume for such systems is discussed, and equations are presented for the determination of the self‐diffusion coefficients of the polymer and the solvent. Conditions under which the mutual diffusion coefficient can be deduced solely from free‐volume considerations are clarified, and a more general version of the free‐volume diffusion theory proposed by Fujita is presented. The further restrictions needed for the theory of Fujita are discussed, and it is concluded that these additional restrictions are responsible for failures of the Fuji

ISSN:0098-1273    

DOI:10.1002/pol.1977.180150302

出版商:John Wiley&Sons, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractA new free‐volume theory is combined with the thermodynamic theory of Flory and the entanglement theory of Bueche to provide a means of predicting the temperature, concentration, and molecular weight dependence of mutual‐diffusion coefficients in amorphous polymer–solvent systems. The predictions of the theory are compared with actual data for the ethylbenzene–polystyrene

ISSN:0098-1273    

DOI:10.1002/pol.1977.180150303

出版商:John Wiley&Sons, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractA method is presented for anticipating condition under which anomalous diffusion effects can be expected for amorphous polymer–solvent systems. The diffusion process is characterized by a dimensionless group called the diffusion Deborah number, and a method for calculating this dimensionless number is presented. Deborah number diagrams are constructed for the unsteady diffusion of ethylbenzene and polystyrene in thin films, and observed diffusion phenomena are discussed on the basis of these diagram

ISSN:0098-1273    

DOI:10.1002/pol.1977.180150304

出版商:John Wiley&Sons, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractMechanical relaxation at hypersonic frequencies is measured using Brillouin spectroscopy for polyisobutylene, atactic polypropylene, polydimethyl siloxane, and polyvinyl acetate. The temperatures of maximum loss determined in the gigahertz range are compared to the published transitions maps for the above polymers. It is found that the hypersonic relaxation data fall on an extrapolation of the secondary main chain glass–rubber relaxation line above the region where the primary and secondary lines merg

ISSN:0098-1273    

DOI:10.1002/pol.1977.180150305

出版商:John Wiley&Sons, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractWe consider the internal viscosity (IV) of polymer molecules in solution, and investigate how the IV might depend on solvent viscosity η0. From the Kirkwood model of a polymer, we derive in a nonrigorous manner two equations containing an IV, one equation valid for low η0and the other for high η0, and we show that in these respective cases the coefficient of the IV is independent of η0and linearly dependent on

ISSN:0098-1273    

DOI:10.1002/pol.1977.180150306

出版商:John Wiley&Sons, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractThe problem of a polyelectrolyte near the rod limit is formulated incorporating both the short‐range stiffness of the backbone (the “wormlike chain”) and the electrostatic interaction between segments taken as a Debye–Húckel potential. By the use of a physically valid approximation an expression is derived for the mean‐square extension length of a short polyelectrolyte chain. Some remarks are made on the relationship between the electrostatic interaction and the usual excluded‐volume problem for polym

ISSN:0098-1273    

DOI:10.1002/pol.1977.180150307

出版商:John Wiley&Sons, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractThermally stimulated discharge has been used in the past to diagnose and estimate the magnitude of electrical polarization in polymers. Nevertheless, molecular characterization of operative phenomena by this technique alone is often a difficult task. In the present work, infrared attenuated total reflection spectroscopy has been used to investigate the origin of thermally stimulated discharge currents near 200°C in externally unpolarized films of polyacrylonitrile (PAN). Spectroscopic analysis of thermally degraded films reveals some unsaturation of the PAN backbone and possibly the generation of cyanide ions. Opposite surfaces in a solvent‐cast film give different spectra, indicating a gradient in chemical degradation products across the film thickness. Data suggest that nonuniform generation of charged species and unsaturated bonds gives rise to internal potentials in PAN. The origin of thermally stimulated currents in PAN near 200°C is thus believed to be associated with the onset of chemical degradat

ISSN:0098-1273    

DOI:10.1002/pol.1977.180150308

出版商:John Wiley&Sons, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractLight scattering from polybutene‐1 films prepared by tubular extrusion was studied in order to investigate its crystalline superstructure and the deformation mechanism. Analysis of the light‐scattering patterns together with electron micrographs, indicate the existence of sheaflike crystalline superstructures. The sheaves are aligned nearly side by side with their axes preferentially oriented perpendicular to the machine direction. TheHvscattering patterns exhibit a “butterfly” appearance. Analysis of the patterns in terms of scattering and azimuthal angles at which the scattering intensity is a maximum yields information on the size and shape of the sheaflike texture. The information should be of importance in studies of anisotropic crystal growth caused by molecular orientation in the melt and of the deformation mechanism of the texture. The deformation behavior should be representative of that of different parts of spherulites, at least qualitatively; the deformation of the texture along the machine and transverse directions corresponds to deformation of equatorial and meridional regions of a spherulite, respe

ISSN:0098-1273    

DOI:10.1002/pol.1977.180150309

出版商:John Wiley&Sons, Inc.    

年代:1977

数据来源: WILEY

摘要:

AbstractThis paper reports of a study on eutectic solidification of the quasi binary system of unfractionated isotactic polypropylene and the dentritic growing diluent pentacrythrityl tetrabromide. This system was characterized by a eutectic‐type experimental phase diagram with a eutectic composition of 68% (w/w) of polypropylene. The eutectic temperature was found to depend on kinetics, and was established by differential scanning calorimetry to be 122 and 102°C at a cooling rate of 0.5 and 32°C/min, respectively. A remarkeable nucleating effect of the primary diluent crystals was observed in the solidification of diluted polypropylene solutions. Here the eutectic horizontal was located at a temperature which was 15°C higher than in the eutectic solutions exceeding the temperature at which the pure polymer crystallized from the melt by 8°C. The eutectic microstructures produced were found to depend on the rate of solidification, which was varied by pulling the polypropylene solutions through a fixed temperature gradient of 3°C/mm at different speeds ranging from 0.2 to 80 mm/hr. At rates lower than 3 mm/hr the polymer and the diluent crystallized simultaneously from the eutectic solution in a uncoupled mode of growth, forming a coarse structure of diluent crystals and isotactic polypropylene spherulites with dimensions of about 0.1 mm. At higher speeds the simultaneous crystallization of the macromolecules and solvent molecules proceeded in a co‐operative manner with a nonplanar growth front. A rodlike eutectic microstructure was produced, in which diluent rods, lined up in the growth direction, were dispersed in a polypropylene matrix. The lateral dimension λ1of these rods were found to depend on the growth rate R in the following way: λ12R= 10−9mm3/sec, and ranged from 0.3 to 1.0 μm. This was in accord with values calculated by using the current theory of rod eutectic growth of Jac

ISSN:0098-1273    

DOI:10.1002/pol.1977.180150310

出版商:John Wiley&Sons, Inc.    

年代:1977

数据来源: WILEY