RAFT synthesis of a thermally responsive ABC triblock copolymer incorporating N-acryloxysuccinimide for facile in situ formation of shell cross-linked micelles in aqueous media

A poly(ethylene oxide) (PEO)-based macromolecular chain transfer agent (macro-CTA) was employed to demonstrate the controlled polymerization of N,N-dimethylacrylamide (DMA) in anhydrous 1,4-dioxane at 70 °C using reversible addition-fragmentation chain transfer polymerization. This macro-CTA was then used to mediate the statistical copolymerization of DMA and the reactive monomer N-acryloxysuccinimide (NAS), forming a diblock copolymer of PEO-b-(DMA-s-NAS). Subsequent chain extension with N-isopropylacrylamide (NIPAM) yielded a PEO-b-(DMA-s-NAS)-b-NIPAM thermally responsive triblock copolymer. In aqueous solution at room temperature the triblock copolymer chains exist as unimers but form micelles when the solution temperature is raised above the lower critical solution temperature (LCST) of the NIPAM block. The hydrodynamic dimensions and micellization temperatures depend on the length of the NIPAM block. Incorporation of the NAS units into the triblock copolymer allows for facile formation of uniform shell cross-linked micelles by reaction with difunctional primary amines in aqueous media. These shell cross-linked micelles swell when the solution temperature is lower than the LCST of the NIPAM block.