Synthesis of Poly(N-isopropylacrylamide)−Poly(ethylene glycol) Miktoarm Star Copolymers via RAFT Polymerization and Aldehyde−Aminooxy Click Reaction and Their Thermoinduced Micellization

A facile synthetic pathway to poly( N -isopropylacrylamide) (PNIPAM)−poly(ethylene glycol) (PEG) miktoarm star copolymers with multiple arms has been developed by combining reversible addition−fragmentation chain transfer (RAFT) polymerization and aldehyde−aminooxy “click” coupling reaction. Star PNIPAM with aldehyde functionalized core was initially prepared by the RAFT arm-first technique via cross-linking of the preformed linear macro-RAFT agents using a newly designed aldehyde-containing divinyl compound 6,6′-(ethane-1,2-diylbis(oxy))bis(3-vinylbenzaldehyde) (EVBA). It was then used as a multifunctional coupling agent for the subsequent formation of the second-generation PEG arms via the click coupling reaction between its aldehyde groups and aminooxy-terminated PEGs. The thermoresponsive micellization behavior of PNIPAM−PEG miktoarm star copolymer with different PEG arm numbers in water was also investigated. Opportunities are open for thermoinduced intermolecular or intramolecular micellization of PNIPAM−PEG miktoarm star copolymers via controlling the content ratio of PNIPAM and PEG, forming multimolecular micelles and unimolecular micelles, respectively.