Novel amphiphilic and photo-responsive ABC 3-miktoarm star terpolymers: Synthesis, self-assembly and photo-responsive behavior

Novel amphiphilic and photo-responsive ABC 3-miktoarm star terpolymers consisting of hydrophilic poly(ethylene glycol) monomethyl ether (MPEG), hydrophobic polystyrene (PS) and azobenzene-containing poly[6-(4-methoxy- azobenzene-4′-oxy) hexylmethacrylate] (PMMAZO) were synthesized by a combination of atom transfer radical polymerization (ATRP) and click chemistry. MPEG was first end-capped by an epoxide ring, which was opened by sodium azide for the preparation of the modified MPEG bearing reactive azide group and hydroxyl group (MPEG-(OH)(N₃)). Click chemistry was then performed to conjugate α-alkynyl-ω-diethylamino-PS and MPEG-(OH)(N₃) for the preparation of a block copolymer with reactive hydroxyl group at the junction point (MPEG(-OH)-b-PS), which was further esterified with 2-bromoisobutyryl bromide to prepare the macroinitiator with reactive bromo group at the central point (MPEG(-Br)-b-PS). Finally, an azobenzene-containing PMMAZO arm was introduced into the diblock copolymer by ATRP of 6-(4-methoxy-azobenzene-4′-oxy) hexylmethacrylate monomer (MMAZO) initiated with macroinitiator MPEG(-Br)-b-PS for the preparation of ABC 3-miktoarm star terpolymer (MPEG)(PS)(PMMAZO). The self-assembled morphologies of the star terpolymers in selective solvents changed from bowl-shaped structures to multibowl-shaped structures with the lengthening of the hydrophobic chains (PS or PMMAZO). Photo-responsive investigation showed that the different aggregation states had a great effect on the photo-induced isomerization behaviors. These results may provide guidelines for the design of effective photoresponsive anisotropic materials.