Commercial triblock polymers (Kratons) consisting of polystyrene and a polydiene were characterized via gel permeation chromatography and small-angle x-ray scattering in order to determine the amount of free polystyrene and diblock material and to clarify the effect of these polymeric impurities on the morphology of solvent-cast samples. Gel permeation chromatography measurements revealed the Kratons to consist of 80–85% triblock, 15–20% diblock, and trace amounts of free polystyrene. Pure triblocks, impurity-doped pure triblocks, the Kratons, and a postpolymerically degraded Kraton were examined with regard to the effect of polymeric impurities on morphology. Small amounts (<5%) of free polystyrene induce a regularization of the glassy domains, while increased amounts of this homopolymer apparently lead to diffuse phase boundaries. The presence of diblock polymer results in a loss of macrolattice details, indicating the presence of less ordered and more diffuse glassy domains.
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Fetters et al. (1972) studied this question.