摘要:

The effect of annealing on the low-angle x-ray diffraction patterns from drawn and rolled samples of nylon 66 is investigated, and the results are compared with those obtained on single crystals. Two periodicities are observed for annealing in the lower range of annealing temperatures, the longer period being approximately twice the shorter, hence possibly the result of a “doubling” mechanism. In samples annealed at higher temperatures a large temperature-reversible change in long spacing is observed, which can be explained by partial melting. Small changes in long spacing at lower temperatures can be accounted for by changes in the lattice structure.

ISSN:0022-2348    

DOI:10.1080/00222347708208749

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

The relaxation phenomena of two semicrystalline polymers, poly(vinyl fluoride) and poly(vinylidene fluoride) were studied by a dilaitometric technique in the temperature range from—30°C to 200°C. The premelting (Tαc), upper [Tg(U)] and lower glass [Tg(L)] transitions are observed for both polymers, as well as a transition in PVF2which is sensitive to thermal history. Comparison of our results with previous work, in most cases at higher frequencies, as well as thermal treatment of PVF2allow us to make assignments and calculate activation energies for the relaxations. Certain characteristic quantities are given, namely, T < Tg(L)/Tg(L), Tg(L)/Tm, and Tαc/Tm, as well as αΔgand ΔαTg.

ISSN:0022-2348    

DOI:10.1080/00222347708208750

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

The relaxation phenomena of two semicrystalline polymers, polyoxymethylene and poly(ethylene oxide), were studied by a dilatometric technique in the temperature range—30 to 200°C. Polyethylene was also investigated, in order to compare property-structure relations. The premelting (Tαc) and upper glass [Tg(U)] transitions are observed in all three polymers. Comparison of our results with previous work, at higher frequencies in most instances, as well as thermal treatment of one of our samples (polyoxymethylene) allow us to make the assignments and calculate the activation energies for the relaxations. Certain characteristic quantities are given: [T < Tg(L)/Tg(L)/], Tg(L)/Tm, and Tαc/Tm, as well as ΔαTgand αΔg.

ISSN:0022-2348    

DOI:10.1080/00222347708208751

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

Chemical relaxation for cis-l,4-polybutadiene crosslinked at 7000 kg/cm2by γ-irradiation was compared with that for one crosslinked at atmospheric pressure. The degree of thermal degradation was similar in both specimens, but the specimen crosslinked at 7000 kg/cm2formed fewer new networks in the initial stage than the specimen crosslinked at atmospheric pressure. The G value for the formation of crosslinking points was proportional to the-0.5 power of the dose rate at high pressure. This indicates that the radiation-induced crosslinking at high pressure proceeds in a chain reaction as proposed from the high G value in a preceding paper. The lower formation of new network chains for the specimens crosslinked at 7000 kg/cm2is concluded to be due to lower mobility of polymer radicals that crosslink by recombination near the clusters of crosslinking points produced by the chain reaction.

ISSN:0022-2348    

DOI:10.1080/00222347708208752

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

Parabola density and radius is shown to decrease as the testing temperature increases. Furthermore, both the density and radius of the parabolas depend on their position on the fracture surface: their magnitude decreases as the distance from the notch increases. Finally, a criterion for parabola formation based on two mechanisms, plastic flow activation and craze initiation, is discussed.

ISSN:0022-2348    

DOI:10.1080/00222347708208753

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

Measurement of translational diffusion coefficients by laser light scattering has been proposed as a convenient, rapid, and accurate method for characterization of macromolecular species in solution. We have determined diffusion coefficients at infinite dilution in various solutions of a series of narrow molecular weight polystyrene samples and found that the data are consistent with only one of two studies reported in the literature. The concentration dependence of the diffusion coefficient for molecules of different particle weight is investigated, and the infinite dilution values are used to access the unperturbed hydrodynamic dimensions and the excluded volume. The diffusion data are compared with the corresponding intrinsic viscosity values and related to the particle weight. Finally a simple method for evaluating macromolecular polydispersity is described and applied to two polystyrene samples with broad molecular weight distribution.

ISSN:0022-2348    

DOI:10.1080/00222347708208754

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

The crystal structure of poly(ethylene sulfide) has been determined by electron diffraction. The analysis was based on the combined use of single crystal and fiber diffraction data. The refined structure consists of chains with glide symmetry, and is in essential agreement with a model previously determined by x-ray diffraction. A test for the validity of a kinematic approximation to the electron scattering, based on the conservation of chain symmetry, is introduced.

ISSN:0022-2348    

DOI:10.1080/00222347708208755

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

Electrical polarizations in as-cast and electrically polarized films of stretched and unstretched polyacrylonitrile have been measured with the thermally stimulated discharge technique. Preferential orientation of nitrile side groups in polarized specimens is inferred from birefringence and x-ray diffraction experiments, but the contribution of observed persistent electrical polarization appears to be small. The major contribution is concluded as being due to trapped space charges, some part of which may be associated with residual solvent molecules. Small ordered regions within polyacrylonitrile are expected to play a role in development of each contribution to final persistent electrical polarization.

ISSN:0022-2348    

DOI:10.1080/00222347708208756

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

Kraton 1101, a styrene—butadiene—styrene triblock copolymer (SBS), was blended with homopolymers of styrene (PS) of various molecular weights by dissolving in mutual solvents. All polyblends cast from mixed solvents of tetra-hydrofuran and methyl ethyl ketone were found to be plasticlike. Stress-strain curves of these materials all exhibited a yield point and a flat drawing region. Samples can be stretched beyond 500% strain without fracture. Blends containing high amounts of added PS (>40%) showed stress-whitening effects. Most samples undergo necking when strained beyond the yield point. However, the necked regions are rubbery and exhibit high elasticity rather than irreversible drawing. Dynamic mechanical data of stretched and unstretched polyblends show that the former have enhanced loss tangent region between the primary glass transition loss peaks of styrene and butadiene blocks. The increased loss tangent is due to the decreased storage modulus values of the stretched samples, while the loss moduli remained unchanged. Stress-strain data of gradient (layered) polyblends are also presented.

ISSN:0022-2348    

DOI:10.1080/00222347708208757

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor

摘要:

Electron micrographs of a series of polyblends of poly(styrene-b-butadiene-b-styrene (SBS) and polystyrene (PS) are presented. These poly blends were cast from three different solvents, i.e., tetrahydrofuran—methyl ethyl ketone (THF/ MEK), benzene—heptane, and carbon tetrachloride. PS of four different molecular weights were used. It is shown that when the molecular weight of PS exceeds that in the block copolymer, a third phase in the form of “islands” is formed. Lamellarlike structures are formed in the block domains upon the addition of homopolymer. Stretching perturbs the morphology of the block domains somewhat, and produces craze marks in the PS islands. The craze marks are removed upon annealing. These results are discussed in conjunction with the observed mechanical behavior of the same polyblends reported in Part I of this series.

ISSN:0022-2348    

DOI:10.1080/00222347708208758

出版商:Taylor & Francis Group    

年代:1977

数据来源: Taylor