Influence of associative dynamic covalent cross-links on poly(ethylene oxide)-block-polystyrene vitrimers

Vitrimers are polymer networks cross-linked by associative dynamic covalent bonds, which achieve bond exchange through an addition-elimination mechanism. This allows the network to fluctuate its topology while still maintaining connectivity. Converting a block copolymer to a vitrimer potentially offers an additional pathway toward controlling self-assembly. In this work, we study how adding associative dynamic covalent bonds affects the block copolymer order-disorder transition temperature (T_ODT) and nanostructure. To prepare model block copolymer vitrimers, low molecular weight poly(ethylene oxide)-block-poly(styrene-stat-4-((4-vinylbenzyl)oxy)benzaldehyde) block copolymer precursors were synthesized using a two-part synthetic scheme. The styrenic block was then cross-linked with a diamine crosslinker to form a vitrimer that undergoes an imine metathesis cross-link exchange reaction. The combination of small angle X-ray scattering (SAXS) and oscillatory dynamic mechanical analysis (DMA) were used to measure the effect of cross-link density on the T_ODT and accessible morphologies of the block copolymers.