Analysis of the phase behaviour in ternary polymer blends based upon Flory's equation-of-state theory

Abstract

The phase behaviour in ternary blends consisting of three chemically different homopolymers was analysed by the extended version of Flory's equation-of-state theory. To avoid arbitrary adjustment of the equation-of-state parameters, polystyrene (PS), poly(vinyl methyl ether) (PVME), poly(2,6-dimethyl-1,4-phenylene oxide) (PPE) and polybutadiene (PB) were used as model polymers. Thus, the pure-component properties were fixed by this process. The unknown set of binary exchange interaction parameters X ij and Q ij were obtained either by fitting the theoretical phase diagram to the experimental one using X ij and Q ij as adjustable quantities or from the experimentally known X ij and Q ij values. Using these data of X ij and Q ij it was found that the calculated binary phase diagrams fit the experimental ones qualitatively well. Up to this point the theory has corroborated its validity for two-component systems. Spinodals of three different ternary model blends were calculated over a wide temperature range. The first mixture, PS(1)/PVME(2)/PPE(3), consisted of two binary blend combinations with lower critical solution temperature ( LCST) and one with upper critical solution temperature ( UCST) behaviour. In the second example a closed miscibility gap was found in the ternary blend despite all binary mixtures being compatible. As a third model mixtures of PPE(1)/PS(2)/PB(3) were used. At low temperature a one-phase regime was found at ø 3<0.07. Raising the temperature increased the compatibility and finally a LCST at the PPE(1)/PS(2) side of the composition triangle occurred.