Dual thermo- and photo-responsive micelles based on miktoarm star polymers

We report the synthesis and characterization of three novel azobenzene-containing miktoarm star polymers AB(3) (M-n = 14 800, D-M = 1.22, M-n = 17 400, D-M = 1.10 and M-n = 26 200, D-M = 1.12) as well as their self-assembly properties in water. The three polymers are composed of an azopolymer and three identical arms of poly(N,N-diethylacrylamide) (PDEAA), featuring thermo-responsive properties. By carefully selecting the polymerization degree of PDEAA, and consequently the hydrophobic/hydrophilic ratio, a specific miktoarm polymer has been identified that forms stable micelles in water as is clearly revealed by Transmission Electron Microscopy (TEM). In addition, the thermo-and photo-responsive properties of the polymeric micelles in water were investigated. Encapsulation of Nile Red was probed via fluorescence spectroscopy as well as its release from the loaded probes triggered by UV irradiation, which causes a trans-to-cis isomerisation of the azobenzene moieties.