Generation of large and locally aligned wormlike micelles in block copolymer/epoxy blends

Abstract

A dispersion of wormlike micelles, empirically found in some block copolymer (BCP) / epoxy blends, has been reported to produce a significant toughening of epoxy networks. In this study, a rationale procedure to generate and trap large and locally aligned wormlike micelles in an epoxy matrix is reported. A BCP / epoxy / hardener blend was selected that was homogeneous at the polymerization temperature but became nanostructured in the course of polymerization leading to hexagonally packed cylinders (HPC) domains. When a similar BCP with a molar mass about three times larger than the first one and with the same ratio between blocks was used, the nanostructuration into HPC domains was frustrated by diffusional limitations of the large cylindrical micelles generated. A morphology consisting of a dispersion of large and locally aligned wormlike micelles was trapped in the cross-linked epoxy. The selected BCP was polystyrene (PS)-b-poly(ethylene oxide) (PEO), with molar masses M = 43 kDa or 136 kDa and a mass fraction of PEO close to 25 wt %. The network precursors were based on diglycidylether of bisphenol A (DGEBA) and 4,4´-methylenebis(2,6-diethylaniline) (MDEA). Low- and high-molar-mass BCP generated, respectively, HPC domains and wormlike micelles, as supported by TEM images and SAXS spectra.