摘要:

The crystal lamella is well established as a basic structural unit of most semicrystalline polymers. It is also accepted that the chain axis is generally not parallel to the normal to the large flat lamella surfaces, but inclined at some angle to it. Due to the random orientation of lamellae in bulk polymers where spherulitic growth predominates, no direct method exists for determining . However, the angle has been determined by acid etching bulk samples and then using electron microscopy techniques on fragments. An alternative approach is utilized in this work. The etched fragments, after suitable washing procedures, were sedimented to form an oriented mat. An x-ray diffraction technique was employed in which the regions of high pole density for several crystallographic planes were determined. From these results, the inclination angle was determined to be 40.4°, with a standard deviation of 1.5°. This study represents the first time that an x-ray pole figure technique has been used to determine chain inclination in isotherm-ally crystallized PE.

ISSN:0022-2348    

DOI:10.1080/00222348708248062

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

A recently developed nonequilibrium thermodynamic theory of continuum rheology is combined with a generalized definition of thermomechanical transitions, to produce a single equation for interrelating the basic variables (stress o, strain rate ε, pressure p, temperature T, and structure ℊ) at a transition. Specialization of ℊ to represent uncrosslinked polymers leads to incorporation of molecular weight M as a variable. New predictions are thus made for the glass transition [Tg(M), Tg(p), Tg(ε) and others] and compared successfully with data. Particularly remarkable are the results that 1/Tgis a piecewise linear function of In M, and T is piecewise linear with p. Comparable results and confirmation with data arise when applying the theory to the liquid-liquid transition, Tll(M). For random copolymers, application of a single mixing rule to the transition equation leads to a prediction of Tgas a function of composition and the Tgifor the homopolymers (components i). This relationship reduces, in various cases, to several familiar equations in which the parameters were simply empirical, thus providing an interpretation of those parameters and defining restrictions applicable to each case. Finally, an alternative interpretation of ℊ in terms of free volume allows the theory to be extended to other systems, including those with small molecules.

ISSN:0022-2348    

DOI:10.1080/00222348708248063

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Dielectric and structural properties have been studied for solution-mixed PVDF/PMMA polyblend samples up to a maximum PVDF weight fraction (W) 0.4. Crystallization of PVDF has been observed in polyblends with PVDF weight fractions 0.4 and 0.3. Analysis of XRD results shows that the pure PVDF as well as the polyblend samples (with W = 0.3 and 0.4) have phase III PVDF crystals. Dielectric parameters, ε′ and ε″, have been measured in the temperature range 40°–140°C and frequency range 100 Hz-1 MHz. The dielectric constant of the polyblend samples falls in between those of the pure components and increases with the PVDF content. The dielectric loss thermograms of PMMA show the β relaxation of the polymer, which may have contribution from the α relaxation also. A part of the αarelaxation of PVDF is observed in its dielectric loss thermograms. A small hump is observed in the dielectric loss thermograms of the polyblends which could be due to the β relaxation of PMMA and the glass transition of the amorphous phase of the polyblends. Charge carrier trapping appears to make a large contribution to the dielectric parameters.

ISSN:0022-2348    

DOI:10.1080/00222348708248064

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Dielectric and IR measurements were carried out for copolymers of isopropyl methacrylate with methacrylic or acrylic acid at various content units. The acid units introduced into isopropyl methacrylate polymer chain formed acid dimers and free acid units in the neighborhood of isopropyl methacrylate units. According to the segmental mode relaxation of main chains (α process), the motion of main chains was found to be restricted by acid dimers formed among acid groups, and reinforced by the free acid units. The acid dimers and free acid units acted even on the local mode relaxation of isopropyl methacrylate side chains. The relaxation strength of the α process (Δα) for copolymer samples increased with temperature. The increase in Δαwas attributed to an increase in the number of motional units caused by breakdown of the acid dimmers. The dissociation energy (ΔH0) of the acid dimmer could then be estimated from the temperature dependence of Δεα.

ISSN:0022-2348    

DOI:10.1080/00222348708248065

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Some detailed investigations recently carried out on plasma-polymerized organosilicon films have revealed a number of phenomena which may be related to a phase transition taking place at ca. 270 K. The existence of this effect is confirmed by measurements of the temperature dependence of the thermal expansion coefficient of these films, by DSC measurements, and by measurements of the temperature dependence of the dielectric constant. It was found that the observed phase transition effect appears to be related to the presence of water molecules in the film volume. The water molecules form aggregates strongly bound to the film structure and stay there even under vacuum and at high temperature (to ca. 450 K).

ISSN:0022-2348    

DOI:10.1080/00222348708248066

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The dielectric relaxation of poly(phenyl methacrylate) and two poly(methoxy-substituted phenyl methacrylate)s was studied over the frequency range from 30 Hz to 3 × 105Hz and the temperature range from −100°C to 170°C. Each sample shows three relaxation processes, termed α, β, and γ, within the temperature ranges 90° to 130°C, 20° to 90°C and −60° to −20°C, respectively. The α and β processes were attributed to the micro-Brownian motion of the main chain and the entire side chain, respectively. The γ process was suggested to be associated with the motion of methoxy phenyl groups at the end of the side chain.

ISSN:0022-2348    

DOI:10.1080/00222348708248067

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The phenomenon of antiplasticization was examined for poly-vinyl chloride containing 10 phr tricresyl phosphate, by means of dynamic mechanical tests and with constant strain rate equipment, using both tension and plane-strain compression deformation modes. While the activation energy for both α and β relaxations was decreased by the addition of the plasticizer, the magnitude of β dispersions decreased and the modulus increased over a temperature range lying between the α and β transitions of the plasticized polymer. Similar changes were found with respect to the yield stress measurements, from which a contour diagram was drawn showing the strain rate/ temperature relationship of antiplasticization. The values of activation energy for yield phenomena were found to lie between those obtained for the α and β relaxations. The activation volume, on the other hand, was found to increase over the same temperature range in which antiplasticization is observed.

ISSN:0022-2348    

DOI:10.1080/00222348708248068

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor