Photoinduced morphology change in ionic supramolecular block copolymer†

Abstract

Physically mixing two dissimilar polymers often results in a macroscopically segregated blend with poor optical clarity and mechanical properties. Previously, we demonstrated that chain end functionalization of immiscible polymer blends with oppositely paired acid and base groups leads to an ionic supramolecular block copolymer with electrostatically stabilized microdomains that suppress macroscopic phase separation. In this work, a functionalized polydimethylsiloxane with a photochromic diarylethene (DAE) end-group (PDMS-ω-DAE) is blended with a sulfonic acid end-functionalized polystyrene (PS-ω-SO₃H), forming an ionic supramolecular block copolymer with tunable morphology by light. When the DAE is irradiated with UV light, it triggers an isomerization from the ring-opened (DAE–O) to the ring-closed (DAE–C) form. The light-induced conformational change in the chain-end group chemistry substantially alters the ionic junctions, leading to a phase structure difference in the solid-state from hexagonally packed cylinders (HEX) to lamellae (LAM). After UV radiation, the more localized positive charge on DAE–C led to stronger ionic bonds between the two dissimilar blocks, while the repulsion between adjacent DAE–C groups increased. The stronger electrostatic repulsion along the interface resulted in increased interfacial area per polymer chain and thus induced such phase transition. The light-induced phase transition of this system demonstrates that the ionic interactions can be tuned on-demand to create different morphologies from a single polymer blend.