Hydrogen bonding reinforcement as a strategy to improve upper critical solution temperature of poly(N-acryloylglycinamide-co-methacrylic acid)

Abstract

Hydrogen bonding reinforcement via copolymerization of N-acryloylglycinamide (NAGA) with methacrylic acid (MAA) is employed as a strategy to improve the upper critical solution temperature (UCST) to a biologically relevant range. P(NAGA-co-MAA) copolymers with MAA molar fraction in the range of 1–81 mol% are synthesized via reversible addition–fragmentation chain transfer (RAFT) polymerization. The UCST (3.5–37.5 °C) of the copolymers scales with MAA molar fraction in the range of 10–60 mol% when measured at pH 4 and 1 wt% concentration. Using a copolymer with a suitably high UCST as a macromolecular chain transfer agent, doubly thermoresponsive nanogels consisting of P(NAGA-co-MAA) copolymer as the shell and cross-linked poly(N-isopropylacrylamide) (PNIPAM) as the core are synthesized via RAFT aqueous dispersion polymerization. The nanogels show distinct thermal transitions with both upper and lower critical solution temperatures (UCST and LCST).