UCST-driven self-assembly and crosslinking of diblock copolymer micelles

Abstract

The upper critical solution temperature (UCST) behaviour of poly[oligo(ethylene glycol) monomethylether methacrylate] (POEGMA) in 1-octanol was exploited to self-assemble and crosslink micellar aggregates. Four diblock copolymers, POEGMA-block-poly(N-isopropylacrylamide) (POEGMA-b-PNIPAM), POEGMA-b-poly(N,N-diethylacrylamide) (POEGMA-b-PDEAM), and two examples of POEGMA-b-[PNIPAM-co-poly(pentafluorophenyl acrylate)] (POEGMA-b-(PNIPAM-co-PPFPA)), containing different amounts of activated PFP esters, were found to reversibly self-assemble into well-defined spherical micelles upon cooling in 1-octanol, as evidenced by dynamic light scattering (DLS) and electron microscopy. Transition temperatures, measured by turbidity and DLS, were around room temperature and the PNIPAM and PDEAM blocks did not significantly influence the critical temperature of the POEGMA block compared to homo POEGMA. The aggregates exhibited an inverted morphology compared to PNIPAM core–POEGMA shell micelles accessible through a thermally triggered self-assembly in water exploiting the lower critical solution temperature (LCST) behaviour of PNIPAM. Inverted micelles with PNIPAM-co-PPFPA coronae in 1-octanol were shell crosslinked using a diamine and subsequently transferred into water. This procedure yielded cage-like structures with swollen POEGMA cores and crosslinked PNIPAM shells. The shells reversibly collapsed onto the cores when heated above the LCST of PNIPAM, providing particles with novel architecture and the potential to host and release guest molecules by a thermal trigger.