Light Scattering and Phase Separation Studies on Cyclohexane Solutions of Six-Arm Star Polystyrene†

Abstract

Light scattering and phase separation experiments were performed for four six-arm star polystyrene (6SPS) samples with weight-average molecular weights Mw of 9.62×104 to 1.16×106 in cyclohexane below the theta temperature (34.5 °C). From the former experiment, the apparent second virial coefficient J was obtained as functions of the polymer volume fraction φ and temperature T, along with the spinodals. In the latter experiment, the concentrations of coexisting two phases were determined as functions of T. The critical point Tc determined from the coexisting curve was lower than that for four-arm star polystyrene (4SPS) when compared at the same Mw. As was the case for 4SPS and linear polystyrene in cyclohexane, J for 6SPS at each T in a region of large φ was represented by a universal function of φ/P0.1 regardless of P (the volume of the polymer chain relative to that of the solvent molecule), although it differed from the common function previously found for the other two types of polystyrene. It was concluded that the solubility of 6SPS higher than that of 4SPS in cyclohexane as indicated by the lower critical point is attributable to the chain-end effect.