Stimuli-induced multiple dissociation and micellization transitions of random copolymers

Abstract

A novel thermo- and light-responsive random copolymer poly(o-nitrobenzyl methacrylate)-co-2-(2-methoxyethoxy)ethyl methacrylate-co-oligo(ethylene glycol)methacrylate (P(NBMA-co-MEO₂MA-co-OEGMA)) was synthesized by atom transfer radical polymerization (ATRP). This amphiphilic random copolymer self-assembled into spherical micelles with a PNBMA core and a PMEO₂MA/POEGMA corona in aqueous solution. Aggregates were formed when the temperature increased above the lower critical temperature (LCST). Upon UV irradiation, the transformation of hydrophobic PNBMA into hydrophilic poly(methacrylic acid) (PMAA) induced the disruption of the initial micelles and the release of the encapsulated fluorescent dye, Nile Red, into water. The accordingly obtained hydrophilic random copolymer P(MAA-co-MEO₂MA-co-OEGMA) exhibited thermo- and pH-responsive behavior. Further increasing the temperature or decreasing the pH, P(MAA-co-MEO₂MA-co-OEGMA) formed PMEO₂MA/POEGMA-core or PMAA-core micelles with the re-encapsulation of Nile Red. This random copolymer has great potential in applications such as controlled release and selective encapsulation.