Poly temperature-composition phase diagram

Fig. 3.21 Temperature-composition phase diagram for poly(benzyl-L-glutamate) in dimethyl formamide. Dashed line indicates areas of insufficient data. (From Miller et al. (94))...

Fig. 14 Creation of a single specimen polymer blend phase diagram from orthogonal polymer composition and temperature gradients. The polymers are polystyrene and poly(vinyl methyl ether) (PVME) a composition library placed orthogonal to a temperature gradient b completed gradient library polymer blend phase diagram. White points are data derived from traditional measurement for comparison. See text for details, (b reproduced with permission from [3])...

Blends of polystyrene/poly(2,6-dimethyl-l,4-phenylene oxide) and polystyrene/poly(vinyl methyl ether) were investigated by IGC over wide composition and temperature ranges. Flory-Huggins free energy parameters were obtained and are discussed as the criterion for thermodynamic miscibility. From the temperature variation of the free energy parameter, phase diagrams for both blends were obtained. 

Sophiea et al. published the first classical composition-temperature phase diagram, working with the semi-IPN net-polyurethane-mter-poly(vinyl chloride) [Sophiea et al., 1994b]. They found a lower critical solution temperature, LCST = 120°C below this temperature the system was one-phased, and above, two-phased. Such behavior is now known to be characteristic of most polymer blends (see Chapter 2). 

Typical phase diagrams that illustrate these principles are presented in Fig. 3.8 for isotactic poly(propylene)-alky phenol mixtures (24) and in Fig. 3.9 for poly (N,N -sebacoyl piperazine) (23) with various diluents. At the higher isotactic poly (propylene) compositions only liquid-solid curves are observed that result in typical melting temperature depression. Although at lower polymer concentrations... 

Another example refers to the transition from the liquid-crystalline to the crystalline state. While studying the phase equilibrii mi in the system poly (p -benzamide), dimethylacetamide (+LiCl), a diagram was obtained which is reproduced in Fig. 7- The compositions of the coexisting phases (isotropic and anisotropic) were determined experimentally. While conducting measurements in the region above lOO C, it was found that on holding the system for one or two days at this temperature both phases pass irreversibly into the gel state, which is accompanied by a... 

The comparison of the phase behavior of semi-IPNs based on almost miscible polymers—linear PS and poly-a-methylstyrene cross-linked by DVB and mixtures of the corresponding homopolymers—has shown that for homopolymer blends only one glass transition is observed, its position obeying the Fox equation. Simultaneously, for semi-IPNs there were two glass transitions, far from the glass transition temperatures of the components, for the same compositions where linear blends are miscible. A difference in phase behavior between blends and semi-IPNs seems to be evident. However, no phase diagrams allow one to determine the mechanism of phase separation. 

In the case of the PBI blends discussed above, phase separation takes place a few degrees above the glass transition temperature for most blend compositions. This can be seen from the phase diagram for PBI/Ultem poly (ether imide) blends, as shown by Karasz and MacKnight. This suggests that the miscibility which is observed is a metastable phenomenon which is controlled by kinetic factors. The observed phase separation also indicates that it will be difficult to melt process the blends in the miscible state, due to the reasons already discussed. 

At one given temperature the composition of, and phase equilibria in, a ternary aqueous solution can be represented on an isothermal triangular diagram. The construction of these diagrams has already been described. Poly-thermal diagrams can also be constructed, but in the case of complex systems the charts tend to become congested and rather difficult to interpret. 

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