Thermal induced mobility of self-assembled platelets of polyethylene-block-poly(ethylene oxide) in liquid precursors of unsaturated polyester thermoset

We report the variation of the molecular assembly and crystallinity of polyethylene-block-poly(ethylene oxide) (EEO, 1400 g mol⁻¹) in a non initiated liquid resin of unsaturated polyester (UP). We particularly focus on the driving force that governs the variation of the molecular assembly of the block copolymer in the UP resin upon heating. For this purpose, we performed a set of experiments combining time resolved in situ SAXS and WAXS measurements upon heating and cooling. Upon heating, SAXS shows that the inter-distance of the EEO domains decreases dramatically for temperature above 75 °C (between 90 and 30 nm for the initial system at room temperature vs 9 nm at 110 °C) suggesting that the initially homogeneously dispersed EEO domains undergo aggregation. This is consistent with the macroscopic phase separation observed in such temperature range. In situ WAXS shows that the onset of the aggregation coincides with the melting of the PE domains suggesting that the flexibility of the platelets plays an important role in their aggregation. Upon cooling, peculiar behaviour is observed for the systems with higher EEO content, with an irreversible structure formation leading to macroscopic EEO rich domains dispersed in continuous UP rich phase.