Decoration of shell cross-linked reverse polymer micelles using ATRP: A new route to stimuli-responsive nanoparticles

We demonstrate the use of atom transfer radical polymerization (ATRP) to graft polymers onto preformed shell cross-linked reverse micelles (SCRM). Reverse polymer micelles are first obtained in organic solvents and stabilized by cross-linking of the shell using the photoinduced dimerization of coumarin groups (>310 nm). The structurally locked SCRM are then used as micellar macroinitiators for further polymerization from their surface of monomers such as styrene and dimethylaminoethyl methacrylate (DMAEMA) via ATRP. The decoration of an outer corona of PDMAEMA renders the nanoparticles containing a hydrophilic core soluble in water, with the solubility being sensitive to changes in pH and temperature. In addition, such decorated SCRM are light-responsive., The photoinduced cleavage of cyclobutane bridges (<260 nm) leads to the de-cross-linking of the shell and thus the disintegration of the micellar aggregates. The characterization results, using size-exclusion chromatography (SEC), dynamic light scattering (DLS), and transmission electron microscope (TEM), show an excellent control over the reactions, the molar mass, and the polydispersity of SCRM before and after the surface-initiated ATRP. The "decoration" of SCRM offers a new route to designing stimuli-responsive polymer nanostructures that cannot be prepared through only block copolymer self-assembly.