摘要:

AbstractA study of the average molecular optical anisotropy 〈γ2〉 of tetrahedral lattice polyethylene chains of any length has been carried out by using Markov processes. The results of this treatment include simplified models of polymer chains, as well as more elaborate models, which are in current

ISSN:0449-2978    

DOI:10.1002/pol.1971.160090601

出版商:John Wiley&Sons, Inc.    

年代:1971

数据来源: WILEY

摘要:

AbstractA comparative study of the average molecular optical anisotropy 〈γ2〉 of the polyoxyethylene chain,\documentclass{article}\pagestyle{empty}\begin{document}${\rm R} \hbox{---} {\rm O}\rlap{--} ({\rm CH}_2 {\rm CH}_2 {\rm O}\rlap{--} )_n {\rm R}$\end{document}where R = CH3, H andnis the degree of polymerization of the molecule, was carried out for the different internal rotational models considered in Part I of this series. In particular, the results obtained show that the condition of interdependence between internal rotational angles of nearest‐neighboring bonds increases the average molecular optical anisotropy by about 4% (n≫ 1), compared with the case of independent rotations. This increase is much weaker than in polyethylene chains, for which it is about 20% under analogous co

ISSN:0449-2978    

DOI:10.1002/pol.1971.160090602

出版商:John Wiley&Sons, Inc.    

年代:1971

数据来源: WILEY

摘要:

AbstractElectron spin resonance spectroscopy has been used to study the effects of 15 MeV electrons, x‐rays, and ultraviolet radiation on poly‐4‐methylpentene‐1 (TPX) both at 77°K and at room temperature. At least seven identifiably different paramagnetic species are observable in unstabilized oxygen‐free TPX after irradiation, and additional species exist in the stabilized grades. The species which predominates under most conditions is interpreted as being due to the loss of hydrogen from a main‐chain tertiary carbon atom; interpretations of most of the other species are also given. Oxygen is found to diffuse rapidly into the polymer and to react with the free radicals to form peroxy species. In the absence of oxygen the radiation damage is expected to lead ultimately to crosslinking or double‐bond formation, or with oxygen to degradation. The general nature of the free radicals produced by electron or x‐ray irradiation is the same, but there are significant differences for ultraviolet irradiation. The observed spectra for irradiated TPX and their interpretations are in good agreement with the spectra and later interpretations for irradiated polypropylene, but are in less satisfactory agreement with the published papers on polybutene‐1 and pol

ISSN:0449-2978    

DOI:10.1002/pol.1971.160090603

出版商:John Wiley&Sons, Inc.    

年代:1971

数据来源: WILEY

摘要:

AbstractNative celluloses of various biological origins, as well as regenerated celluloses were examined by electron microscopy after suitable dispersion. In all cases the specimens were found to be composed of a common filamentary unit which is rectangular in cross section and has the approximate dimensions 35 × 20 Å. It is suggested that these are the basic morphological units of cellulose; they are therefore called protofibrils. For protofibrils of regenerated cellulose it is shown that: (1) the molecular contour length greatly exceeds the protofibril length, (2) the mass of the protofibril corresponds to that of a single molecule, and (3) the protofibril length increases with molecular weight. Additionally, high resolution electron micrographs of native and regenerated protofibrils show an apparent axial texture with a periodicity of about 40 Å. From these observations and the knowledge that the molecular chain axis is aligned parallel to the protofibril axis, a model of the protofibril is deduced. The model consists of a ribbon which is pleated on itself so as to form a planar zigzag structure of rectangular cross section. This supersedes a previously proposed model of circular cross section. The structure is composed of a single folded, chain, arranged so that the short extended segments between the folds are parallel to the protofibril axis. The protofibril is thus regarded as the morphological expression of the cellulose molecule. Microfibrils and protofibrils often exhibit kinks, the angle between the kinked portions being 120°. This phenomenon is satisfactorily explained by the protofibril model and in fact provides good support for it. Finally, various properties of cellulose are considered in relation to the model. By contrast with the earlier crystalline–amorphous concepts of cellulose fine structure, it is suggested that protofibrils are completely crystalline structures, and that the properties of cellulose may be understood by considering processes that occur at the level of the protofibril as a

ISSN:0449-2978    

DOI:10.1002/pol.1971.160090604

出版商:John Wiley&Sons, Inc.    

年代:1971

数据来源: WILEY

摘要:

AbstractNew structural phenomena which can be produced in polymers at low temperatures or by the action of high forces are described and discussed. Experimental evidence supports the argument that the deformation of polymers can develop not only as a result of conformational changes of the macromolecules proper but also by transformation of more complex structural formations. The consequence of this phenomenon is the possibility of large deformations far below the glass‐transition temperature in a crystalline polymer with well‐developed supermolecular structure. This type of deformation takes place without molecular orientation. Another phenomenon discussed is the sharp change of supermolecular structure in crystalline polymers caused by the action of a shock wave. These effects ought to be connected with an energetic rather than entropic deformation mechanism because the transformations occur at a supermolecular level. Thus, there can be two extreme types of deformation processes: the well‐known conformation changes that occur at a molecular level, and the deformation of supermolecular structures. Examples of the pure form of the latter type of mechanism obtained under extreme conditions are

ISSN:0449-2978    

DOI:10.1002/pol.1971.160090605

出版商:John Wiley&Sons, Inc.    

年代:1971

数据来源: WILEY

摘要:

AbstractDrawn and subsequently annealed polyethylene film was restretched along the original draw axis at various temperatures. The internal deformation was analyzed in terms of the structural parameters of a simplified model. The elementary deformations are the rotation of crystals around thebaxis and shear at the crystal interface. The rigidity of the crystal plays an important role during extension; and as a result, disorientation of chains in the crystal occurs at high strain. At the same time, crystals deform in such a way that the crystalline chains tilt about thebaxis along the (h00) plane. This deformation of the crystal is affected by temperature. The increase in long spacing with extension can be interpreted roughly by the changes in structural parameters. The strain in amorphous region in also discussed in relation to these parameters.

ISSN:0449-2978    

DOI:10.1002/pol.1971.160090606

出版商:John Wiley&Sons, Inc.    

年代:1971

数据来源: WILEY

摘要:

AbstractStudies have been made of the secondary relaxation processes in the solid state of a number of polymers containing aromatic groups in the polymer chain. The polymers investigated include one, polystyrene, with the aromatic group in side‐chain positions, and six high polymers in which phenylene rings lie in the main backbone chain. In polystyrene, wagging and torsional motions of the side chain phenyl rings give rise to a low‐temperature δ‐relaxation which is centered at 33°K (1.7 Hz) and which has an activation energy of about 2.3 kcal/mol. Most of the polymers with phenylene rings in the main chain exhibit a low‐temperature relaxation in the temperature region from 100°–200°K. This relaxation process is centered at 159°K (0.54 Hz) in poly‐p‐xylylene, at 162°K (0.67 Hz) in polysulfone, and at 165°K (1.24 Hz) in poly(diancarbonate). In poly(2,6‐dimethyl‐p‐phenylene oxide), two overlapping low‐temperature relaxations are found, one in the range 125–140°K and the other near 277°K (ca. 1 Hz). The low‐temperature secondary relaxation process in all of these polymers is believed to be associated with local reorientational motion of the phenylene, or substituted phenylene, rings or with combined motion of the phenylene rings and nearby chain units. For these low temperature relaxation processes, the activation energy is about 10 kcal/‐mole. The temperature location of the relaxation appears to depend on the specific units to which the phenylene rings are attached and on steric and polar effects caused by substituents on the ring. In the poly‐p‐xylylenes the relaxation is shifted to much higher temperatures by a single Cl substitution on the ring but remains at essentially the same temperature position when dichlorosubstitution is made. The effects of water on the magnitude and temperature location of the observed low temperature relaxations, as well as the implications of the study for other polymers containing aromatic groups

ISSN:0449-2978    

DOI:10.1002/pol.1971.160090607

出版商:John Wiley&Sons, Inc.    

年代:1971

数据来源: WILEY

摘要:

AbstractThe diffusive permeability of waterP, which relates to diffusive flux of water under a concentration gradient of water (measured by diffusion of tritiated water), and the hydraulic permeability of waterK, which relates to the water flux under a hydraulic pressure gradient are defined. For the case of diffusive transport one hasP=KRT/ν1, where ν1is the molar volume of water. The relationship betweenPandKwas investigated as a function of hydrationH, i.e., the volume fraction of water in swollen polymer membranes. The following characteristic features of water permeability are revealed. (a) In the lowhydration region (H<0.2), water permeates by diffusion even under an applied hydraulic pressure gradient andKRT/ν1=P. (b) In the higher hydration regionKRT/ν1is greater thanP, and the ratio ω =KRT/ν1Pincreases nearly exponentially with decrease of (1‐H)/H. Water in this region moves partly by bulk flow under an applied hydraulic pressure gradient but moves only by diffusion in the absence of a pressure gradient. (c) The dependence of logPon (1‐H)/His nearly linear in regions of both high and low hydration but the slopes are different. The transition occurs in about the sameHrange where the discrepancy betweenPandKRT/ν1becomes significant. Excellent agreement was found between the experimental data forPas a function ofHand the theoretical prediction based on the free‐volume concept of diffusive transport in hydrated homogeneo

ISSN:0449-2978    

DOI:10.1002/pol.1971.160090608

出版商:John Wiley&Sons, Inc.    

年代:1971

数据来源: WILEY

摘要:

AbstractThe glass transition temperatures of a number of poly(vinyl phenyl ketones), poly‐(vinyl benzoates), and poly(phenyl acrylates) have been measured by a refractometric method. The effects exerted onTgby the nature and position of the ring substituents and by the different groups binding the pendant phenyl rings to the polyvinyl chain are discussed. The importance of knowledge of the side‐group motions in the glassy state for the interpretation of glass temperature data is emphasi

ISSN:0449-2978    

DOI:10.1002/pol.1971.160090609

出版商:John Wiley&Sons, Inc.    

年代:1971

数据来源: WILEY

ISSN:0449-2978    

DOI:10.1002/pol.1971.160090610

出版商:John Wiley&Sons, Inc.    

年代:1971

数据来源: WILEY