Eight‐arm star polystyrene in methylcyclohexane: Cloud‐point curves, critical lines, and coexisting densities and viscosities

Abstract

Abstract We measured the cloud‐point curves of eight‐arm star polystyrene (sPS) in methylcyclohexane (MCH) for polymer samples of three total molecular masses [weight‐average molecular weight ( M w ) × 10 −3 = 77, 215, or 268]. We found a downward shift of 5–15 K in the critical temperature ( T c ) of the star polymer solutions with respect to linear polystyrene (PS) solutions of the same M w . The shift in T c became smaller as M w increased. The critical volume fraction for eight‐arm sPS in MCH was equal within experimental uncertainty (10–40%) to that of linear PS in MCH. For sPS of M w = 77,000 in MCH, we studied the mass density (ρ) as a function of temperature ( T ). As for linear polymers in solution, the difference in ρ between coexisting phases (Δρ) could be described over t = ( T c − T )/ T c for 1.1 × 10 −4 < t < 4.7 × 10 −3 with the Ising value of the exponent β in the expression Δρ = B t β . Both ρ( T ) above T c and the average value of ρ below T c were linear functions of temperature; no singular corrections were observed. The measurements of the shear viscosity (η) near T c for sPS ( M w = 74,000) in MCH indicated a strong critical anomaly in η, but the data were not precise enough for a quantitative analysis. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 129–145, 2004