Spiropyran-containing water-soluble and photoreversible copolymers

Photoreversibility in polymer design enables the control of physical properties using light, and in concert with water-solubility permits applications in aqueous environments. Inspired by environmental application, the primary goal of this paper is to develop a new synthesis pathway and to characterize the structure and functional behavior of spiropyran-containing photoreversible and water-soluble polymers. A one-step facile acylation reaction yielded the spiropyran-containing acrylate (SPA) monomer. Free radical copolymerization afforded a series of copolymers of SPA and oligo(ethylene oxide) monoacrylate monomer (OEOA) (Mn = 480 g/mol). Thermal analysis, including thermogravimetric analysis and differential scanning calorimetry, revealed the influence of SPA content on copolymer weight loss profile and OEOA side chain crystallization/melting. Copolymers exhibited good water solubility owing to the hydrophilic OEOA side chain. Solution rheology unveiled a shear-thickening effect related to the SPA pendent group and revealed the solution viscosity dependence on polymer concentration in aqueous solutions. In water, the designed spiropyran-containing polymers displayed photoreversibility and exhibited high photo-fatigue resistance with >90% of UV-vis absorbance preserved after five cycles. Preliminary Cu2+ complexation studies with SPA-co-OEOA copolymers indicated 88% removal of Cu2+ after UV irradiation, which suggests opportunities as light-responsive polymers for Cu2+ removal.