A polymer–solvent system with two homogeneous double critical points: Polystyrene (PS)/(n-heptane + methylcyclohexane)

Liquid–liquid (LL) critical demixing loci have been experimentally determined in the (T,P) projection for some polystyrene/solvent systems with nonspecific interaction for (∼ 270 K < T < ∼ 500 K) and (0 MPa < P < 200 MPa). A lower homogeneous double critical pressure and lower homogeneous double critical temperature have been located for a solution of PS (M_w = 2.0 × 10⁶) dissolved in an n-heptane/methylcyclohexane mixture [PS/n-C₇H₁₆/CH₃C₆H₁₁//0.029/0.194/0.777 (wt. fractions)]. That solution forms the first example of a polymer/solvent with nonspecific interaction that exhibits two double critical points. A symmetrical representation of the LL critical loci in the (P,T) plane is developed. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2747–2753, 1999