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

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Abstract
We report on the synthesis and stimuli-responsive self-assembly of novel double hydrophilic Janus-type A7B14 heteroarm star copolymers with two types of water-soluble polymer arms emanating from the two opposing sides of the rigid toroidal β-CD core. Janus-type A7B14 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 β-CD derivative. At first, β-CD-(I)7 was obtained by reacting β-CD with I2 in the presence of PPh3 at 70 °C, which can selectively transform seven primary hydroxyl groups of β-CD into iodine moieties. After converting to β-CD-(N3)7viaazidation of β-CD-(I)7, the subsequent esterification reaction of β-CD-(N3)7 with 2-bromopropionic bromide afforded (N3)7-CD-(Br)14. The ATRP of NIPAM monomer in 2-propanol/DMF mixture at 25 °C using (N3)7-CD-(Br)14 as the multifunctional initiator led to azide-containing 14-arm star polymers, (N3)7-CD-(PNIPAM)14. Well-defined Janus-type double hydrophilic star copolymers were then prepared by the click reaction of (N3)7-CD-(PNIPAM)14 with an excess of monoalkynyl-terminated PDEA. Upon adjusting solution pH and temperatures, (PDEA30)7-CD-(PNIPAM25)14 can reversibly self-assemble into two distinct types of polymeric vesicles with “inverted” nanostructures in aqueous solution.

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