Polystyrene phase separation from PVME

Roth et al. [42] used steady-state fluorescence measurements to study the emission spectra of pyrene and anthracene dyes covalently bonded to polystyrene (PS) upon phase separation from poly(vinyl methyl ether) (PVME). The total fluorescent dye content in the samples was <0.02 mol%. As shown in Figure 25.15a, before phase separation the fluorescence intensity of the spectra decreased slowly with increasing temperature. However, after phase separation (see Figure 25.15b) a sharp increase in fluorescence intensity was observed, which was attributed to the removal of fluorescence quenching of the dye by the local presence of the more polar PVME component in the misdble state. These results showed clearly that the PS/PVME blend displays a lower critical solubility temperature (LCST) type of phase diagram. 

To test this prediction of the crossover from mean-field to Ising-t5q)e behavior, very precise small-angle neutron scattering measurements were completed on blends of deuterated polystyrene (d-PS) and poly(vinyl methyl ether) (PVME) at the critical concentration for a series of temperatures as the one-phase mixture approaches the temperature of phase separation (ie, the critical point Tc in Fig. 7) (61). The data were analyzed by fitting the measured I (q) to the random phase approximation to estimate l(g=0) for each temperature, where the temperature is controlled to 0.01 K... 

In the first category, polystyrene (PS) and poly(vinyl methyl ether) (PVME) have been reported to be compatible when films are cast from suitable solvents.5 But phase separation can be induced in a compatible film simply by heating the mixture to about 150°C. Subsequent slow cooling of the phase-separated mixture resTilts in a compatible film. The thermally induced phase separation behavior of PS-PVME mixture indicates the existence of LOST. The presence of UCST was not reported, althoTigh, according to Patterson s theory, if LOST exists, UCST should also exist. 

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