Effect of Molecular Weight on Blend Miscibility

Excimer fluorescence from a guest polymer blended with a nonfluorescent polymer host is used to study the influence of the molecular weight of the two components on the miscibility. The ratio of the excimer to monomer emission intensities, I D /I M, for poly(2-vinylnaphthalene) (P2VN) is measured in blends with polystyrene (PS). Differential scanning calorimetry (DSC) is employed to establish conditions for miscibility in 35 % P2VN/PS blends from which a criterion for miscibility in low concentration systems may be inferred. Increases in I D /I M above the values expected for miscible systems that occur with increased host molecular weight or guest concentration are analyzed using Flory-Huggins theory. An interaction parameter of 0.020 ± 0.004 is consistent with the fluorescence results over a relatively narrow concentration range.