Synthesis, characterization and self-assembly of ion-bonded amphiphilic A2B miktoarm star copolymers containing an azobenzene unit at the core

An azobenzene-containing supramolecular copolymers, consisted of two polystyrene (PSt) arms and one poly(ethylene oxide) (PEO) arm linked via ionic bond, has been designed and successfully synthesized. Monomethoxy PEO with phenylazobenzenesulfonic acid as the terminus (PEO-Ndouble bond; length as m-dashN-SO3H) was utilized to react with polystyrene carrying tertiary amino group at the middle of the polymer chain (PSt2-N(CH3)2) to form ion-bonded supramolecular star copolymers (PSt2-Ndouble bond; length as m-dashN-PEO) with an azobenzene group at the core based on the interaction between sulfonic acid group and amino group. The obtained copolymers were characterized by 1H nuclear magnetic resonance (1H NMR) and gel permeation chromatography (GPC) techniques. The self-assembly behavior of the copolymers with different molecular weight of PSt was investigated, which shows solid spherical aggregates in water. The aggregation leads to the lower isomerization degree (54%) at the photostationary state in water compared with that in 1,4-dioxane (82%).