摘要:

Comparison is drawn between data obtained from dielectric relaxation and thermally stimulated discharge current (TSDC) measurements on blends of carboxyl-terminated butadiene acrylonitrile (CTBN) with an epoxy resin (ER) obtained by reaction of the diglycidyl ether of bisphenol A (DGEBA) with either triethylenetetramine (TETA) or diamino-diphenylmethane (DDM). The effect of varying the composition of CTBN on the nature of the phase separation was examined using electron microscopy and was also evident from changes in the dielectric spectrum and the calculated activation energy for the molecular relaxation process. The morphology consists of spherical rubber particles dispersed in an epoxy matrix at low levels of CTBN, and at higher concentrations epoxy resin is observed to be precipitated as spheres within the rubbery phase. Detailed analysis of the dipolar spectra indicates that at low concentrations there appears to be some cosolution of the epoxy in the CTBN.

ISSN:0022-2348    

DOI:10.1080/00222349308215484

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The structure development during melt curing of poly(phenylene sulfide) (PPS) is reported. The changes in the structure were monitored using various characterization techniques such as differential scanning calorimetry, thermogravimetric analysis, infrared spectroscopy, and optical microscopy. It was observed that the thermal parameters such as melting point and heat of fusion are very sensitive to the structural changes and can be effectively used to monitor the curing process. The effect of curing environment was also investigated, and it was found that the rate of change of structure is considerably higher in air than in nitrogen. The results are discussed on the basis of the different mechanisms for curing of PPS.

ISSN:0022-2348    

DOI:10.1080/00222349308215485

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The presence of the aliphatic hydroxyl group in poly(ethylene-co-vinyl alcohol) (EVOH) suggests that these copolymers have the potential for forming miscible blends with a variety of polymers containing complementary functional groups such as esters, (meth)acrylates, acetoxys, pyridines, etc. There is a paucity of examples of miscible EVOH blends in the literature, however. Hydrogen bonding, which is very complicated in EVOH copolymers and involves an extraordinary variety of nter- and intramolecular species, plays an important role in the phase behavior of EVOH blends. We have applied an association model to this problem and arrived at the following important conclusion. Miscibie EVOH blends with polymers containing ester or acetoxy groups do exist, but they have lower critical solution temperatures below normal processing temperatures (< 200 °C). This is primarily a consequence of the fact that EVOH copolymers are strongly self-associated, while the interassociation of the hydroxyl groups of EVOH with the carbonyl groups of the complementary polymers is comparatively weak.

ISSN:0022-2348    

DOI:10.1080/00222349308215486

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Transport properties of dichloromethane vapor were measured in atactic polystyrene films (aPS), obtained by casting chloroform ando-dichloro-benzene solutions. The diffusional behavior is characterized by three stages, depending on vapor activity. In the first stage, at low activity, the diffusion coefficient is independent of concentration; the second stage, which occurs above a critical activity, is characterized by concentration-dependent diffusion and by the appearance of anomalous sorption curves; in the third stage the strong polymer-solvent interaction induces structural transformation of the samples. The diffusional behavior of the cast films is very similar to that of aPS films obtained by hot pressing, and also the extrapolated parameters are very close, leading to the conclusion that the structural organization is quite similar in both cases. At low penetrant activity the films cast fromo-dichlorobenzene and dried at 70 °C show a lower sorption than the others; the presence of domains in which the chains are differently packed in such a way as to be impermeable to the vapors in the low range of vapor activity is suggested.

ISSN:0022-2348    

DOI:10.1080/00222349308215487

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Much attention is being devoted to polymer/salt hybrids prepared by dispersing inorganic salts in polymers, because the hybrids have high ionic conductivities (1,2). Many of the investigations have concentrated on the system polyester-alkali metal salts, such as poly(ethy1ene oxide)-NaI (3). A few other polymers, such as poly(viny1idene fluoride) and poly(ethy1ene imine), have been examined as the polymer matrix for dissolving the salts (4, 5). In the field of solid state ionics, an active area of research is the attempt to obtain polymer/salt hybrids with higher conductivity. Most of the investigations have been directed toward the evaluation of conductivity for new polymer-salt systems.

ISSN:0022-2348    

DOI:10.1080/00222349308215488

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor