Hairpin Configurations of Triblock Copolymers at Homopolymer Interfaces

Abstract

The organization of triblock copolymers containing a central block of polystyrene (PS) and two outer blocks of poly(methyl methacrylate) (PMMA), denoted P(MMA-b-S-b-MMA), at the interface of immiscible homopolymers was investigated by dynamic secondary ion mass spectrometry. Selective labeling of either the two end blocks or the central block provided the contrast necessary to determine the spatial arrangements of the blocks at the interfaces. Triblock copolymers at the interface between PS and poly(vinyl chloride) (PVC), poly(2,6-dimethylphenylene oxide) (PXE) and PVC, and PXE and PMMA were investigated. In all cases it was found that the triblock copolymers were organized such that the central block preferentially segregated to one homopolymer whereas the end blocks segregated to the other forming a “hairpin” type of conformation. For different triblock copolymer concentrations, essentially the same distribution of segments at the interface is found, differing only by a scaling factor. Adding excessive amounts of the triblock to the interface, however, causes a substantial broadening, which suggests aggregation of the copolymers at the interface. In comparison to P(S-b-MMA) diblock copolymers of equal molecular weight and composition, the triblock copolymer at lower concentrations produces a larger broadening of the interface. However, for concentrations approaching half the copolymer period, the interfacial broadening for the two cases in similar. In addition, although the central PS block of the triblock is anchored to the interface at both ends, the extension of this block away from the interface is very similar to that seen for the PS block of the corresponding diblock copolymer. © 1992, American Chemical Society. All rights reserved.