Phase separation curves of poly(alpha-methylstyrene) in methylcyclohexane

We report new measurements of the liquid-liquid phase separation curves of poly(alpha-methylstyrene) + methylcyclohexane, for three well-characterized samples of the polymer with number average molecular weights of(A) 19 700, (B) 32 300, and (C) 72 000 g/mol. Sample A (polydispersity index PI = 1.02 ) has a critical point at a mass fraction m(c) of polymer of 0.20 +/- 0.02 and a critical temperature T-c at (305.70 +/- 0.09) K. The critical point f or sample A is not at the apex of the phase separation curve, which indicat es that the polymer was not sufficiently monodisperse to behave as one comp onent. Sample B (PI = 1.02) has m(c) = 0.15 +/- 0.02 and T-c = (318.3 +/- 0 .4) K; this critical point is at the apex of the phase separation curve wit hin our resolution. Sample C (PI = 1.05) has m(c) = 0.11 +/- 0.02 (not the apex of the curve) and T-c= (328.9 +/- 0.4) K. From these measurements, we find a theta temperature Theta of (357 +/- 5)K and an entropy of dilution p arameter psi(1) of 0.49 +/- 0.06. The polymer/solvent interaction parameter chi(1) at T-c for each sample is (A) 0.54 +/- 0.01, (B) 0.56 +/- 0.01, and (C) 0.58 +/- 0.01. The uncertainties for Theta, psi(1), and chi(1) are giv en as one standard deviation.