Synthesis and supramolecular self-assembly of stimuli-responsive water-soluble Janus-type heteroarm star copolymers

We report on the synthesis and stimuli-responsive self-assembly of novel double hydrophilic Janus-type A(7)B(14) heteroarm star copolymers with two types of water-soluble polymer arms emanating from the two opposing sides of the rigid toroidal b-CD core. Janus-type A(7)B(14) star copolymers of N-isopropylacrylamide (NIPAM) and 2-(diethylamino) ethyl methacrylate (DEA), (PDEA)(7)-CD( PNIPAM)(14), were synthesized by coupling atom transfer radical polymerization (ATRP) and click chemistry techniques, starting from a well-defined b-CD derivative. At first, beta-CD-(1)(7) was obtained by reacting b-CD with I-2 in the presence of PPh3 at 70 degrees C, which can selectively transform seven primary hydroxyl groups of b-CD into iodine moieties. After converting to b-CD-(N-3)(7) via azidation of b-CD(I)(7), the subsequent esterification reaction of b-CD-(N-3)(7) with 2-bromopropionic bromide afforded (N-3)(7)-CD-(Br)(14). The ATRP of NIPAM monomer in 2-propanol/DMF mixture at 25 degrees C using (N-3)(7)CD-( Br)(14) as the multifunctional initiator led to azide-containing 14-arm star polymers, (N-3)(7)-CD( PNIPAM)(14). Well-defined Janus-type double hydrophilic star copolymers were then prepared by the click reaction of (N-3)(7)-CD-(PNIPAM)(14) with an excess of monoalkynyl-terminated PDEA. Upon adjusting solution pH and temperatures, (PDEA(30))(7)-CD-(PNIPAM25) 14 can reversibly self-assemble into two distinct types of polymeric vesicles with "inverted'' nanostructures in aqueous solution.