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 7B 14 heteroarm star copolymers with two types of water-soluble polymer arms emanating from the two opposing sides of the rigid toroidal ?-CD core. Janus-type A 7B 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 ?-CD derivative. At first, ?-CD-(I) 7 was obtained by reacting ?-CD with I 2 in the presence of PPh 3 at 70 ?C, which can selectively transform seven primary hydroxyl groups of ?-CD into iodine moieties. After converting to ?-CD-(N 3) 7via azidation of ?-CD-(I) 7, the subsequent esterification reaction of ?-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 ?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-(PNIPAM 25) 14 can reversibly self-assemble into two distinct types of polymeric vesicles with inverted nanostructures in aqueous solution.