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

Abstract

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.