Poly(ionic liquid)s are a subclass of ionic liquids that feature polymerizable groups in either the anion, the cation or both. They are used as building blocks 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 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 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 and characterization of linear (pNiPAAm-SPA-AA) and its incorporation in a sIPN. A series of sIPN hydrogels have been synthesized, each having a different concentration of the (pNiPAAm-SPA-AA) linear copolymer, and their photo-response was analyzed in deionized water and in a series of NaCl solutions (0.5 wt%, 1 wt% and 5 wt%). For the sIPNs containing 100%, 200%, 300% and 400% w/w linear copolymer, the total area contraction after 30 min white light irradiation in deionized water was ≈3%, ≈6%, ≈10% and ≈13%. In conclusion, a linear p(NiPAAm-SPA-AA) copolymer was synthesized and incorporated in a crosslinked PSPA matrix to create photo-responsive sIPNs with finely tuned photo-actuation properties. References: [1] J. Yuan, D. Mecerreyes, M. Antonietti, Prog. Polym. Sci., 2013, 38, 1009-1036. [2] C. Boutris, E. G. Chatzi, C. Kiparissides, Polymer, 38 (1997) 2567-2570. [3] K. Sumaru, M. Kameda, T. Kanamori, T. Shinbo, Macromolecules, 37 (2004) 4949-4955.