A UNIVERSAL RELATIONSHIP FOR DIFFUSION IN TERNARY POLYMER-SOLUTIONS - THE INCOMPATIBLE POLYMERS POLYSTYRENE AND POLYISOBUTYLENE IN BENZENE

This paper reports self-diffusion coefficients determined by dynamic light scattering for polystyrene (PS, probe) in a polyisobutylene (PIB, matrix) over wide ranges of relative molecular weights of the two polymers with benzene as the solvent (theta solvent for PIB at 24.5-degrees-C). The refractive index of benzene is matched with that of PIB, resulting in single-exponential autocorrelation functions in the dynamic light scattering experiments. When the matrix chains are entangled, universal plots are found of the form log (DM)probe versus (C/C(e))matrix over wide ranges of concentration of the matrix where C(e) is the entanglement concentration. This relationship also applies both for M(probe) >> M(matrix) and M(probe) << M(matrix). The previously used logarithmic diagrams of (DM)probe versus (C/C*)matrix are also valid as universal plots but are less sensitive representations. At higher temperatures where there is increased mutual interpenetration of the PIB chains, the PS component is increasingly segregated from the matrix at progressively lower PIB concentrations. The effect is not simply related to C*PIB.