Abstract
We present the synthesis and solution properties of dual stimuli-responsive poly(N-isopropylacrylamide-co-spiropyran acrylate) (P(NIPAAm-co-SPA)) copolymers of varying composition prepared via nitroxide-mediated copolymerization. The resulting copolymers feature molar masses from 40,000 to 100,000 g/mol according to static light scattering and an SPA content of up to 5.3%. The latter was determined by 1H NMR spectroscopy and UV–Vis spectroscopy. These materials exhibit reversible response upon irradiation in polymeric films for a minimum of three cycles; their response in solution to both light and temperature was also investigated in an aqueous TRIS buffer (pH 8). Irradiation was carried out using LED setups with wavelengths of 365 and 590 nm. In aqueous solution, a custom-made setup using a fiber-coupled 200 W Hg(Xe) lamp with 340 and 540 nm filters was used and additional heating of the copolymer solutions during irradiation allowed to study influence of the presence of either the spiropyran or merocyanine form on the cloud point temperature. Hereby, it was found that increasing the SPA content leads to a more pronounced difference between both states and decreasing cloud points in general.
Highlights
Over the last decades, numerous polymeric materials that respond to an external stimulus such as temperature, pH value, or ionic strength have been reported
TheSynthesis polymerizable spiropyran derivative was synthesized according to a procedure reported The polymerizable polymerizable spiropyran derivative was synthesized synthesized according to aa procedure procedure reported by by Raymo and Matyjaszewski et al
Thereby, we found that the temperature response of PNIPAAm and the reversible transition from the spiropyran to merocyanine form of Spiropyran Acrylate (SPA) can be combined
Summary
Numerous polymeric materials that respond to an external stimulus such as temperature, pH value, or ionic strength have been reported. Among these examples of stimuli-responsive materials, fewer studies have reported materials that can respond to more than one trigger, and, in the best case, two orthogonal stimuli have been reported. Temperature is the most applied and extensively investigated, with various studies exploiting the lower critical solution temperature (LCST). PNIPAAm exhibits a lower critical solution temperature (LCST) in water at 32 ◦ C [19], and since its discovery in 1968 has served as a key example for temperature-responsive polymers in aqueous media [20].
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