Dynamic light scattering measurements are reported as functions of concentration and temperature for polystyrenes of well defined molecular weight and polydispersity in a good solvent (toluene) and in Theta solvents (cyclohexane, methylcyclohexane, and deuteromethylcyclohexane) in the homogeneous region but under conditions approaching liquid-liquid demixing, including demixing via spinodal decomposition. The results are compared with DLS measurements reported in the previous paper for demixing via nucleation/growth.