Analysis and Dilute Solution Properties of 12- and 18-Arm-Star Polystyrenes^†

The homogeneity of samples of 12-arm- and 18-arm-star polystyrenes was investigated by ultracentrifugation sedimentation in a 9 solvent and with gel permeation chromatography combined with low-angle laser light scattering. The former method permits the detection of star polymers with different numbers of arms in a sample, and the latter allows the determination of the number of arms in the stars. Light scattering studies revealed that the star polymer coils are expanded from the random walk size in a 9 solvent for the linear polymer. The strong upward curvature at n < 4 in the reciprocal scattering curve of the stars in a good solvent suggests that the average segment density distribution in the stars is more uniform than predicted by the random walk model. Sedimentation velocity and intrinsic viscosity measurements indicate that these highly branched polymers behave hydrodynamically almost like hard spheres in dilute solution.