(388g) A New Type of Unimolecular Polymeric Nanoparticle: Janus Double-Brush Copolymers

Representing a new type of unimolecular nanoparticle, double brush copolymers (DBCs) with each graft site quantitatively carrying two different grafts have been studied in our laboratory.  Two types of DBCs, one with polystyrene and polylactide grafts and the other with polylactide and poly(ethylene oxide) grafts, were synthesized through the preparation of well-defined diblock macromonomers with pendent norbornene groups at block junctions, followed by “grafting through” these macromonomers via ring-opening metathesis polymerization.  Well-defined chemical structures of these DBCs were proven through MALDI and NMR analysis of the macromonomers, as well as GPC analysis of both macromonomers and DBCs.  The nanostructures of DBCs were characterized by DLS, AFM, and TEM.  Specifically, the Janus morphologies of the DBCs with both polystyrene and polylactide grafts were visualized by TEM imaging, providing critical evidence to verify DBCs as Janus nanomaterials.  With amphiphilic nanostructures, the DBCs with both polylactide and poly(ethylene oxide) grafts showed different bulk solution properties as compared with their macromonomer precursors.  Moreover, these amphiphilic DBCs can effectively stabilize biphastic systems, and miniemulsions using these DBCs as surfactants exhibited remarkably high stability.