CO2-Stimulated morphology transition of ABC miktoarm star terpolymer assemblies

The integration of stimuli-responsive polymers with polymeric assemblies enables exquisite control over their nanostructures. Herein, we report the CO2-regulated self-assembly behaviors of a series of amphiphilic miktoarm star terpolymers star-[poly(ethylene glycol)-polystyrene-poly[2-(N,N-diethylamino)ethyl methacrylate]] (μ-PEG-PS-PDEA). These μ-PEG-PS-PDEA assemblies show enhanced CO2-responsibility with the increase in the molecular weight (Mn) of the PDEA segment. For μ-PEG-PS-PDEAx (x represents the Mn of the PDEA block, x = 9.3k, 12.2k, 25k), we observed an unusual sphere/vesicle-to-lamella transition upon CO2 stimulation. As the Mn of PDEA increases from 9.3k to 25k, the morphology of these lamellae evolves from nanophase segregated “E. coli-shaped” nanosheets to nanoribbons, then to nanodiscs. We studied the pH, zeta potential and the microscopy images of the assemblies before and after CO2 stimulation, and accordingly speculated the possible mechanisms for the morphology transformation and the nanophase segregation. Our results indicate that the combination of CO2 stimulation with miktoarm star polymers could potentially extend the horizon of macromolecular self-assembly.