Novel reversible thermoresponsive nanogel based on poly(ionic liquid)s prepared via RAFT crosslinking copolymerization

In this study, a facile strategy for the preparation of thermo‐ and pH‐responsive nanogels through reversible addition–fragmentation transfer (RAFT) crosslinking copolymerization of ionic liquid‐based monomers is demonstrated. The use of chain transfer agents (CTAs) containing carboxyl group in the RAFT polymerizations is the key to producing highly thermoresponsive nanogels. Experimental results demonstrate that the critical gelation temperature of the as‐prepared nanogels can be tuned by adjusting the feed ratio of monomer and CTA. Variable temperature Fourier transform infrared measurements and control experiments indicate that hydrogen‐bonding interactions between the carboxyl groups of CTAs are responsible for the thermoresponsive behaviors of poly(ionic liquid) (PIL)‐based nanogels. Furthermore, PIL‐based nanogels are also found to be pH‐sensitive, and can be further decorated by poly(N‐isopropylacrylamide) (PNIPAAm) via surface grafting polymerization. PNIPAAm‐grafted nanogel aqueous solutions can be reversibly transformed into macrogels upon a change in temperature. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 169–178