Excluded-Volume Effects in Star Polymer Solutions: Four-Arm Star Polystyrene in Benzene

Abstract

Radii of gyration, second and third virial coefficients, and intrinsic viscosities have been determined by light scattering and viscometry for four-arm star polystyrene samples with weight-average molecular weights Mw of 9.1 × 104 to 3.1 × 106 in benzene at 25 °C. They are compared with typical data for linear polystyrene in the same solvent to establish the ratios of the respective properties of the star chain to those of the linear chain at high Mw. The relation between the radius expansion factor and the excluded-volume parameter z for Mw > 3 × 105 comes close to the known relation for the linear polymer in the coil limit and is described by the previously proposed interpolation formula. On the other hand, the viscosity expansion factor vs z plot appears significantly below that for linear polystyrene, the difference remaining to be explained theoretically. The values obtained for the interpenetration function are in the range between 0.43 and 0.46 and about 1.8 times as large as those for the linear polymer. They agree closely with recent Monte Carlo simulation data, but their comparison with the previously constructed interpolation expression suggests that, as in the case for linear flexible polymers, the effect of chain stiffness on the second virial coefficient needs to be considered for Mw below 106.