Resolution of sub-Rouse modes of polystyrene by dissolution

The properties of the softening glass to rubber dispersion of two archetypal amorphous polymers, polystyrene and polyisobutylene, appear to differ greatly. Previously, these differences have been explained by the larger intermolecular coupling between the repeat units in executing the local segmental motions in polystyrene than polyisobutylene. Dissolution of polystyrene into a solvent with a lower glass temperature certainly diminishes the intermolecular coupling and could make the softening dispersion of the polystyrene solution resemble bulk polyisobutylene. Creep compliance measurements of solutions of polystyrene in tri-m-tolyl phosphate are used to show that this expectation is the case. At 17% polystyrene, the properties of the softening dispersion of the solution are nearly identical to that of bulk polyisobutylene, including the appearance of a resolved sub-Rouse mode.