ABC triblock copolymers/epoxy-diamine blends. 1. Keys to achieve nanostructured thermosets

Epoxy thermoset blended with polystyrene-block-polybutadiene-block-poly(methyl methacrylate) triblock copolymers have been investigated before and after the epoxy-amine reaction, coupling different techniques: dynamic mechanical thermal analysis (DMTA), transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). Before reaction, the three blocks self-organize on a nanometer scale, in PS spheres surrounded by PB nodules while the PMMA blocks are solubilized with the epoxy precursors, forming a swollen corona. Using MCDEA as hardener, the domain sizes were found not to be affected throughout the network formation. The final structure is composed of undiluted PS and PB blocks forming a spheres on spheres morphology, most of the PMMA chain remaining embedded in the epoxy network. A partial deswelling of the PMMA brush does occur during the epoxy-amine reaction, resulting in a pure PMMA phase. This phase, evidenced by DMTA, is most likely located at the vicinity of the interface with the PB microdomains. On the other hand, using DDS as hardener induces the phase separation of the PMMA blocks in the early stages of reaction, leading to flocculated, micrometer size elongated nanostructures and opalescent materials. Transparent nanostructurated thermosets were obtained when the following requirement was met: that the PMMA homopolymer remained soluble within the growing thermoset polymer during the whole reaction. The effects of impurities on the triblock behavior have also been studied and compared to the effects of impurities on a diblock behavior.