A new visible light and temperature responsive diblock copolymer

A visible light and temperature responsive diblock copolymer of poly[6-(2,6,2′,6′-tetramethoxy-4′-oxyazobenzene) hexyl methacrylate]-block-poly(N-isopropylacrylamide) (PmAzo-b-PNIPAM) was synthesized via reversible addition–fragmentation chain transfer (RAFT) polymerization by carefully tuning the polymerization conditions. The PmAzo-b-PNIPAM block copolymer forms micelles in water, and the hydrophobic and visible light responsive PmAzo block forms the core of the micelles and the thermoresponsive PNIPAM block keeps the micelles suspended in water. The size of the micelles is firmly correlative with the degree of polymerization (DP) of the PmAzo and PNIPAM blocks. The PmAzo-b-PNIPAM micelles are thermo-responsive and photo-responsive. Aggregation of micelles occurs at temperature above the phase transition temperature of the PNIPAM block, which slightly decreases with the DP of the PmAzo block. The visible-light-induced isomerization of the azobenzene moieties in the PmAzo block leads to a decrease or increase of the hydrodynamic diameter Dh of the micelles depending on the irradiation light wavelength.