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

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.