A Study of Compatible Polymer Mixtures

The compatibility of various compositions of polystyrene (PS)-poly (vinyl methyl ether) (PVME) films and the thermally induced phase separation of such mixtures have been studied using several methods. Density measurements indicate extensive mixing of the PS and PVME chains in compatible PS-PVME films. Vapor sorption measurements have enabled calculation of the PS-PVME interaction parameter X′23 as a function of composition and temperature. The parameter X′23 is negative for compatible PS-PVME films in the composition range 35-65 wt % PVME satisfying the thermodynamic criterion for stability in a binary mixture. The temperature dependence of X′23 for the PS-PVME system suggests the existence of a lower critical solution temperature and an upper critical solution temperature. Vapor sorption measurements also indicate that the diffusion of benzene into a 45.3:54.7 PVME-PS film is Fickian, supporting the notion of extensive mixing of PS and PVME chains in the compatible mixture. Temperature-dependent measurements of spin-lattice relaxation time T1 component, spin-spin relaxation time T2 , and fraction of long T2 component by pulsed NMR indicate that compatible PS-PVME films can be described as microheterogeneous, in which PVME and PS chains, although being extensively mixed, are not completely mixed on the segmental scale. This is to be expected based on excluded volume and geometrical considerations.