Coexistence curve of polystyrene in methylcyclohexane. X. Two-phase coexistence curves for ternary solutions near the tricritical compositions

Tricritical phase equilibrium properties were studied for the ternary solution of two polystyrene homologs in methylcyclohexane by numerical analysis of the generalized Flory–Huggins equation with an empirical interaction parameter and by experimental measurements. For critical solutions at the tricritical molecular weight ratio two-phase coexistence curves were calculated very near to the critical points as 10−7 in the reduced temperature. The shape of the coexistence curves changed markedly depending on the overall compositions of the solution. For the tricritical solution the coexistence curve was asymmetric due to an interference with the critical line but the asymptotic behavior near the tricritical point was not revealed by the present calculation. Two-phase coexistence curves were measured for ternary solutions with the molecular weight M1=1.87×104 and M2=41.2×104 which yielded the molecular weight ratio 22 close to the empirical tricritical value 23 found in literatures. The coexistence curves measured for solutions not far from the tricritical one exhibited the characteristic features calculated for solutions near the tricritical one.