In one aspect, the present invention is directed to a thermally responsive AB diblock copolymer prepared by RAFT polymerization wherein the diblock copolymer comprises poly(N-(3-aminopropyl)methacrylamide hydrochloride)-block-(N-isopropylacrylamide). Nanostructures of the thermally responsive diblock copolymer are formed by molecularly dissolving the diblock copolymer in aqueous solution at room temperature; and increasing the solution temperature to form nanostructures, for example vesicles or micelles. The first RAFT polymerization of an unprotected amino acid based monomer directly in water is also disclosed. The present invention also provides a method of forming shell cross-linked vesicles by adding a RAFT synthesized anionic homopolymer to a solution of the thermally responsive diblock copolymer. A method of forming interpolyelectrolyte complexed micelles or vesicles is also disclosed, the method comprising preparing by sequential aqueous RAFT polymerization a block copolymer comprised of N,N,-dimethyl acrylamide (DMA), N-acryloyl alanine (AAL) and N-isopropyl acrylamide (NIPAM); dissolving the block copolymers into aqueous solution; raising the solution temperature above the lower critical solution temperature of the NIPAM block; allowing the micelle solution to equilibrate; adjusting the pH of the solution to about 5; adding a cationic polymer to the solution; and stirring the solution. The reaction is readily reversed by the addition of a salt solution. In another aspect of the invention a reversible shell cross-linked micelle of a triblock copolymer cross-linked with cystamine is disclosed where a cleaving agent can be added to cleave the micelles. The reaction can be reversed with the addition of tris(2-carboxyethyl)phosphine or dithiothreitol.
 The United States government may own rights to this invention pursuant to grants provided by the Department of Energy (DE-FC26-01BC15317) and the MRSEC program of the National Science Foundation (DR-0213883)