Successive order–order transitions of the hierarchical morphology of a dendron-jacketed block copolymervia subsequent stretching alignment and self-assembly

Abstract

A dendron amphiphile 4′-(3,4,5-trioctyloxybenzoyloxy)benzoic acid (TOB) is designated to bind, via hydrogen bonding, into vinylpyridine blocks of polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP), for a high TOB grafting density of 0.7. Stretching followed by specific annealing enables the TOB-jacketed P4VP blocks, P4VP(TOB)_0.7, to exhibit several liquid crystal (LC) phases with increasingly better packing strength, from bilayer smectic to a highly oriented and hexagonally packed columnar phase; thereby, the global structure of the supramolecular complex PS-b-P4VP(TOB)_0.7 evolves from body-centered-cubic to face-centered-cubic (FCC), then to a highly oriented tetragonally perforated layer (TPL) structure, as evidenced by in situ small- and wide-angle X-ray scattering and transmission electron microscopic images. In particular, captured is the subtle transition of the FCC-packed PS domains, via an epitaxial extension along the 〈110〉 direction, into the perforated layers of TPL. Modulation of the local and global packing sequence via external stretching and annealing proves to be an efficient way in preparing oriented and hierarchically ordered dendron-jacketed block copolymers.