Solvent Effect on Photo / Thermo Responsive behaviour and Application of Poly(N-isopropylacrylamide) End-capped with 4-Propoxyazobenzene in Aqueous Media

Abstract

ABSTRACT The photoisomerisation behaviour of Poly(N-isopropylacrylamide) end-capped with 4-propoxyazobenzene (PNIPAM-Azo-OC3H7) was studied in a conconsolvent mixture of water and dioxane. The trans-cis isomerisation rate of PNIPAM-Azo-OC3H7 was mildly affected by the solvent compositions. Interestingly, the addition of dioxane could not only change the lower critical solution temperature (LCST) of PNIPAM-Azo-OC3H7 aqueous solution but also accurately controlled the increase or decrease in the LCST during UV irradiation. The LCST change (ΔT) could be adjusted from −5.0°C to 10.0°C, which was affected by the cononsolvent type, the second solvent and polymer concentration. Transmission electron micrographs (TEMs) showed that the PNIPAM-Azo-OC3H7 solution could self-assemble into different nano-micelles in different amounts of miscible solvents. UV irradiation of PNIPAM-Azo-OC3H7 solution was found to induce different changes in particle shape and size, which in turn led to either decrease or increase in the LCST changes in this novel responsive system. Furthermore, Nile red was tested here as a fluorescence probe for photo-induced release from PNIPAM-Azo-OC3H7 micelles, and the results suggested that this polymer could be used as a hydrophobic chemotherapeutic drug carrier for controlled release.