Blends binary, demixing

Macrophase separation after microphase separation has been observed in an AB block copolymer/homopolymer C blend (Hashimoto et al 1995). Blends of a PS-PB starblock copolymer (75wt% PS) and PVME homopolymer were prepared by solvent casting. Binary blends of PS and PVME exhibit a lower critical solution temperature (LCST), i.e. they demix at high temperatures. The initial structure of a 50% mixture of a PS-PB diblock and PVME shown in Fig. 6.20(a) consists of worm-like micelles. Heating led to macrophase separation as evident... 

Until recently, very little quantitative information was available on blends of block copolymers. The literature is summarized in Table 6.3. Hoffman et al. (1970) reported microscopic demixing of blends of PS-PB diblocks, with two maxima in the domain size distribution, but with no evidence tor macrophase separation. These findings must be treated with caution in the light of more recent results. Hadziioannou and Skoulios (1982) used SAXS and SANS to investigate the morphology of binary blends of PS-PI diblocks, and binary PS-PI/PS-PI-PS or PS-PI/PI-PS-PI blends or blends of the two types of triblock. They found that the blends were microphase separated, and that the sharpness of the interface was not reduced in blends compared to neat copolymers. The transition between a lamellar and a cylindrical structure was shown to depend primarily on blend composition. In contrast, the transition from a lamellar to a disordered phase at... 

The phase behavior of binary blends becomes much more complex if one relaxes the assumption of incompressibility. Then both liquid-liquid demixing and liquid-vapor phase separation are possible and the system is described by two scalar order parameters - density and composition (p, 4>) or the two densities of the species (pcos j Phd)- The interplay between the two types of phase... 

A demixing induced crystallization is shown in Figure 3.33 (route B in Figure 3.25) for the binary PCL/PS 40/60 blend. 

Tanaka and Nishi (1985) were the first to report about the existence of coupling between crystallization and demixing in crystallizable blends. A competition between demixing and crystallization is seen in binary blends of a semicrystalline and an amorphous polymer when the crystallization curve and the miscibility gap intersect. The morphology of blends exhibiting such behavior is determined by the ratio of the rate of crystallization and of demixing. Four important situations can be distinguished (Fig. 3.41) ... 

Relevant to the study of ternary blends of PCL/phenoxy/PVME are the data on PCL/phenoxy and PCL/PVME binary blends discussed earlier (Sects. 16 and 18.2). Also relevant are studies of phenoxy/PVME blends. Both Robeson et al. [167] and Uriarte et al. [168] demonstrated miscibility over the whole composition range as evidenced by single, composition-dependent TgS the latter group also demonstrated that the binary blends are characterised by LCST behaviour with a rather flat cloud-point curve located at about 430-440 °C over most of the composition range. The same workers determined heats of demixing from the magnitudes of relevant endothermic transitions obtained by differential scanning calorimetry. 

A phase diagram of a binary polymer blend can be derived from the Tg of the demixed phases under the following conditions ... 

In blends that show a miscibility gap in their composition range, the phase transitions and the superstructure can be markedly affected by the contemporary presence of both crystallization and demixing phenomena, depending on the concentration of the crystallizing component. A competition between the kinetics of the two phenomena can be observed in blends with crystalline and amorphous components when the region of phase separation intersects the crystallization range, as schematically shown in Figure 10.7 for a binary system with a UCST [46]. 

---