A new thermoresponsive polymer of poly(N-acryloylsarcosine methyl ester) with tunable LCST
Poly(N-acryloylsarcosine methyl ester) (PNASME), a thermoresponsive N-ester substituted polyacrylamide has well-defined molecular weight and low Ð, was synthesized by solution RAFT polymerization. The synthesized PNASME exhibited a cloud point temperature (Tcp) or lower critical solution temperature (LCST) at 44.0 oC. It was found that various factors could affect Tcp of PNASME, e.g, the polymer molecular weight, the polymer concentration, the salt effect on Tcp following the order of Hofmeister series, urea increasing Tcp, and phenol decreasing Tcp, respectively. The mechanism of urea and phenol inducing the phase transition of PNASME was revealed by 2D NOESY spectra, and how the hydrogen bonding between PNASME and the solutes of urea and phenol affected the phase transition of PNASME was clarified out. The contrary effect on the Tcp of PNASME induced by urea and phenol affords the convenience to adjust the thermoresponse of PNASME, and the tunable thermoresponse of the diblock copolymer of poly(N-acryloylsarcosine methyl ester)-block-poly(N-isopropylacrylamide) is demonstrated. The present study is believed to offer a new pathway to tune the solution behavior of thermoresponsive polymers.