Dual photo- and thermo-responsive copolymers based on spiropyrans : synthesis and self-assembly into nanostructured materials

Grimm, Oliver GND

Within the scope of this thesis, various photo-responsive (spiropyran) and thermo-responsive (2-(2-(2-methoxyethoxy) ethoxy) ethyl acrylate or N-isopropylacrylamide) moieties were incorporated with copolymers or block terpolymers, and their dual-responsive behaviour in solution, micellar systems and polymeric membranes investigated. First, dual-responsive copolymers were synthesised using photo-responsive nitrobenzospiropyran acrylate (SPA) with a thermo-responsive moiety, either N-isopropylacrylamide (NIPAAm) or 2-(2-(2-methoxyethoxy) ethoxy) ethyl acrylate (TEGA). The copolymerisation of both combinations to form P(NIPAAm-co-SPA) and P(TEGA-co-SPA) is possible by free radical polymerisation thermally initiated with AIBN. A more sophisticated method, nitroxide-mediated polymerisation, was then applied since it permits the formation of well-defined hydrophobic copolymer macroinitiators that are suitable for block extension. This simplified the determination of the degree of polymerisation and enabled the formation of amphiphilic block terpolymers. Upon optimisation, a set of water-soluble copolymers from each thermo-responsive comonomer were prepared. The seven P(NIPAAm-co-SPA) copolymers contained 0 to 5.28 mol% of SPA according to 1H-NMR and an absolute molar mass ranging from 32,000 to 124,000 g/mol. The five P(TEGA-co-SPA) copolymers contained 0 to 16 mol% of SPA and an absolute molar mass 37,000 to 58,000 g/mol. In both cases, the amount of SPA in the monomer mixture is reflected in the final copolymer composition. To investigate the dual responsive behaviour, the copolymers were dissolved in a pH 8 buffer solution, where the best photo-responsive behaviour is observed in the pH-range from 2 to 10. Upon irradiating the copolymers at 340 nm, a change in absorbance at 550 nm indicates the amount of SPA in the zwitterionic merocyanine form increases. This process could be reversed by irradiation at 540 nm and could be repeated at least three times.


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