Multi-stimuli-responsive polymers enabled by bio-inspired dynamic equilibria of flavylium chemistry

As part of a complex equilibria network with other chemical species, flavyliums, the chromophoric component of anthocyanins, hold great potential for use in functional polymers. This study presents the successful syntheses of polymers containing two distinct flavylium-structures, generated via post-modification of a parent polymer synthesised using reversible addition-fragmentation chain transfer (RAFT) polymerisation. The selective modification of acetophenone moieties enabled precise tuning of the polymers' properties, which are strongly influenced by the markedly different chemical characteristics of flavyliums and the other species in equilibria with them. The synthesised flavylium-containing polymers exhibit multi-stimuli responsiveness to variations in solvent, pH, light, and temperature, thereby introducing intricacy and viable functionality to the polymer system. The surface activity and critical aggregation concentrations (CAC) of the synthesised polymers were studied using profile analysis tensiometry (PAT), revealing distinct aggregation and self-assembly behaviours. Fractal-like aggregates formed by the flavylium-containing polymers were investigated using cryogenic electron microscopy (Cryo-EM) and small-angle X-ray scattering (SAXS). This research bridges the colourful dynamic equilibria of flavylium chemistry with polymer chemistry, paving the pathway for further investigations into flavylium-polymer interactions and the development of tuneable material properties of responsive polymers.