摘要:

A modified version of the Leary-Henderson-Williams equilibrium thermodynamic theory is used to predict microstructural properties for tapered poly(styrene-butadiene) diblock copolymers containing a random copolymer between the blocks. The interphase thickness, interphase volume fraction, and repeat distance are all predicted to increase as the volume fraction of the added random copolymer increases, whereas the microphase-separation temperature is shown to decrease. Comparison of model results with experimental data for tapered poly(styrene-isoprene) diblock copolymers reveals good agreement for small amounts of the additional random copolymer (up to about 20 vol%). Trends indicate that, at large fractions of random copolymer, the tapered block copolymer may be in a homogeneous state when the nontapered block copolymer would be phase separated under the same conditions.

ISSN:0022-2348    

DOI:10.1080/00222348908212325

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

PVDF/PMMA polyblends have been investigated over the entire composition range by DSC, IR. XRD, SEM, and dielectric techniques. Crystallization of PVDF is observed in the polyblends with PVDF content ≥20 wt%. DSC results indicate depression of crystalline melting temperature of PVDF crystals in the polyblend samples. Glass transition temperature of the amorphous phase is also lowered with the increase in the PVDF concentration. XRD and IR absorption results show the predominance of phase III crystals in pure PVDF as well as polyblend samples. SEM micrographs show spherulitic crystal structure of PVDF; the size of the spherulites is about 18 μ. These spherulites become gradually less distinct as the concentration of PMMA increases in the polyblend samples. 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. The αc-relaxation, which has generally been observed for phase II PVDF, does not appear in the dielectric loss thermograms of PVDF and of polyblend samples, indicating the absence of phase II PVDF in our samples.

ISSN:0022-2348    

DOI:10.1080/00222348908212326

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Melt flow properties, solution behavior, and mechanical properties of the sulfonated EPDM ionomers obtained by sulfonation of high molecular weight EPDM in the presence of a phase transfer catalyst were studied. The results showed that these ionomers can be processed more easily than those obtained by sulfonation without a phase transfer catalyst. Addition of zinc stearate lowered the melt viscosity, represented by the torque value of a Brabender torque rheometer, and increased both the flow activation energy and the tensile strength. Both melt viscosity and tensile strength increased with sulfonate content of the ionomer up to 30 meq/100 g. An increase of neutralization degree barely affected the melt viscosity and flow activation energy, but enhanced the tensile strength up to an equivalent ratio of 2 and also lowered the solution viscosity. Cations used in neutralization exerted significant influence on the properties of the ionomers. For monovalent cations, melt viscosity and tensile strength decreased with decreasing ionic potentials, while for divalent cations, with increasing ionic potentials and with decreasing covalent character, tensile strength decreased but melt viscosity increased. The order of decreasing solution viscosity was almost the same as that of melt viscosity, except for the reversal of Ca and Mg. Addition of ethyl alcohol decreased the solution viscosity of the ionomer, while addition of ethylene glycol increased the solution viscosity.

ISSN:0022-2348    

DOI:10.1080/00222348908212327

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The deformation at room temperature of thick (ca. 2 mm) and thin (ca. 1000 Å) films of polybutene was characterized by electron microscopy and electron x-ray diffraction. The thin films, as studied, draw by micronecking whereas the thick films draw uniformly. In both types of samples the details of the deformation process varied with the orientation of the lamellae in the original spherulitic structure; in all cases, however, the lamellae broke up into “mosaic” blocks prior to uniform fibril formation. The tetragonal-hexagonal phase transformation accompanying the deformation of fresh polybutene films generally appeared to occur within the blocks except in those situations in which the lamellae are being drawn perpendicular to the molecular axes, that is, parallel to the lamella surface; in the latter case the tetragonal form can be at least partially retained until unfolding and fibril formation occurs.

ISSN:0022-2348    

DOI:10.1080/00222348908212328

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Films of isotactic polypropylene (iPP) were quenched to between 5° and 40°C, with a very thin substrate. Wideangle x-ray diffractograms for these samples show that above 25°C the monoclinic phase appears, in addition to the smectic. The amorphous fraction was derived from the study of transport properties; it was the same for all the samples and different from the value obtained from density data. It is suggested that at room temperature, just before the monoclinic phase appears, there is a complex structural reorganization, in which the smectic phase contains many voids and imperfections. This makes the use of density data unapplicable for determination of the phase composition. The variation of transport properties was studied during the aging of the sample quenched at 25°C. From this study it is suggested that the aging phenomenon occurs in two stages: a rapid decrease of the amorphous fraction followed by a progressive reduction of mobility of the amorphous chains.

ISSN:0022-2348    

DOI:10.1080/00222348908212329

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Elastic moduli of an amorphous cellulose chain in helix form are calculated starting from energy maps describing the values of the relative energy of different conformations caused by the rotation of the intra- and inter-cellulose-monomer β-glucosidic linkages. Indications are evident that the amorphous cellulose chain is in a “prestretched” conformation in its native form and environments.

ISSN:0022-2348    

DOI:10.1080/00222348908212330

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The characteristic textures of the mesophase in ethyl-cyanoethyl cellulose/dichloroacetic acid cholesteric liquid crystalline solutions were studied under different conditions by means of a polarized light microscope with a hot stage. It was found that the mesophase textures were directly related to the concentration and the temperature of the solutions. With increasing concentration, the disk-like texture changed, first, into an oily-streak texture and then into a randomdomain texture. The disk-like and oily-streak mesophase textures also changed gradually with time into the focalconic texture or the pseudoisotropic texture. Changes in the texture with temperature were affected by thermodynamic and kinetic factors. In the equilibrium state, the mesophase aggregates were smaller at higher temperature than at lower temperature, but their birefringence did not decrease with the temperature.

ISSN:0022-2348    

DOI:10.1080/00222348908212331

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor