摘要:

Molecular weight dependence of polymer packing density in the amorphous state as predicted by the intermolecular bundle (IMB) model of Kargin, Kitaigorodskii, and Slonimskii, by the entangled statistical coils (ESC) model of Flory and Bueche, and by the statistical chain folding (SCF) model of Robertson is compared with experimental data for density and surface tension of molten polyethers. An experimentally observed sudden drop of ρ and γ at some characteristic molecular weight Mcrand the subsequent gradual increase of these parameters with MW is best accounted for by the SCF model. On the basis of some phenomenological considerations in conjunction with an extension of the SCF model to allow for the segregation of macromolecular coils at MW = Mcr, an empirical equation predicting the dependence of the zero-shear rate viscosity of high-molecular weight polymers on the 3.5 power of MW is obtained. The relationship between Mcrand the “critical” viscosity molecular weight Mcis briefly discussed.

ISSN:0022-2348    

DOI:10.1080/00222347508219418

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

A study has been made of the crystallization of amylose from stirred solutions. It was found that a highly turbulent flow can induce fibrillar crystallization in a 5% solution of amylose in 1NKOH and in 35% chloral hydrate. Furthermore it was observed that these fibrillar crystals were insoluble in the original solution after crystallization.

ISSN:0022-2348    

DOI:10.1080/00222347508219419

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

Linear polyethylenes have been cross-linked both chemically and by irradiation. In each case oriented samples have been produced both by cold drawing followed by annealing and by crystallization under strain. Elastic moduli have been measured in different directions and over a wide range of temperatures. Structural investigations have shown that all the samples have lamellar morphology, but the lamellae are differently oriented, being perpendicular to the draw direction in strain-crystallized materials but inclined at 45° to this direction in the cold-drawn materials.

ISSN:0022-2348    

DOI:10.1080/00222347508219420

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

The relative amounts of the α- and γ-crystalline forms of nylon 6 obtained from the glassy state under different crystallization conditions have been studied by the X-ray diffraction procedure described in the previous paper. The weight fraction of the γ-form decreases with increasing crystallization temperature above 160°C and that of the α-form increases. Growth of the γ-form is predominant in crystallization at 100°C and of the α-form at 200°C. Differential scanning calorimetry and density data are presented. A large amount of a thermally unstable form is included in the γ-form crystallized from the glassy state at lower crystallization temperatures and is transformed into the a-form with annealing at 200γC. Thermal stability of the γ-form obtained from the glassy state was quantitatively investigated and discussed.

ISSN:0022-2348    

DOI:10.1080/00222347508219421

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

Electron microscopy reveals a characteristic structural organization consisting of poorly organized spherulites with an open fibrous texture in which the strands appear to be built up from microfibils. X-ray and birefringence results are also discussed.

ISSN:0022-2348    

DOI:10.1080/00222347508219422

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

Diffusion coefficients for oxygen in narrow range molecular weight distribution samples of polystyrene (anionically prepared) have been measured at 25°C. Diffusion coefficients decrease asymptotically with increasing molecular weight up to a molecular weight of about 20 × 103. Results have been interpreted semiquantitatively in terms of the free volume theory of diffusion, the chain ends contributing relatively more to the free volumes of the low molecular weight polymers at subglass transition temperatures.

ISSN:0022-2348    

DOI:10.1080/00222347508219423

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor

摘要:

Tensile experiments on polystyrene (PS) in various pressure-transmitting fluids were performed up to 4.0 kbar to study the effects of test media on the mechanical behavior of amorphous polymers under pressure. The fracture stress of PS in silicon oil environment was found to depend strongly on the viscosity of oil and the strain rate of tensile tests. As the strain rate increases, the fracture mode at 2.5 kbar was observed to change from brittle to ductile at some critical strain rate, a rate which shifts to a higher value with decreasing viscosity of silicon oil. In addition, creep fracture experiments conducted at 2.5 kbar in silicon oil with different viscosities suggested that the environmental effects are governed by the rate of diffusion of the environmental liquid into the tensile specimen. Fourier transform infrared measurements performed on specimens fractured in silicon oil environment under pressure proved that the penetration of liquid takes place mainly through the porous structure of the crazes. It was also found, surprisingly, that water, which hardly affects the mechanical behavior of PS at atmospheric pressure, becomes a significant stress-cracking agent under higher pressure.

ISSN:0022-2348    

DOI:10.1080/00222347508219424

出版商:Taylor & Francis Group    

年代:1975

数据来源: Taylor