Photo-responsive semi-interpetrating network hydrogels based on poly(ionic liquids) and a poly(N-Isopropylacrylamide-Spiropyran-Acrylic Acid) copolymer

Poly(ionic liquids) are a subclass of ionic liquids that feature polymerizable groups in either the anion, the cation or both. They are used as a building block for a wide range of materials which can be used for a broad spectrum of applications, including conducting materials in solar cells, lithium rechargeable batteries, actuators and other electrochemical devices [1]. Poly(N-isopropylacrylamide) (pNiPAAm) is known to exhibit a lower critical solution temperature (LCST) in an aqueous medium [2]. By incorporating other co-monomers in the pNiPAAm network, such as spiropyran (SPA) photochromic units, materials which exhibit are both thermo- and photo-responsive can be synthesized [3]. By crosslinking a poly(ionic liquid), such as tributylhexylphosphonium 3-sulfopropylacrylate (PSPA), in the presence of a linear poly(N-isopropylacrylamide-co-spiropyran-co-acrylic acid) (pNiPAAm-SPA-AA) copolymer, a semi-interpenetrating network (sIPN) was synthesized. The following research focuses on the synthesis of and characterization of linear (pNiPAAm-SPA-AA) and its incorporation in a sIPN. The photo-induced shrinking of the resulting sIPN was characterized in the presence of deionized water and NaCl solutions of different concentrations