Thermo- and pH-Responsive Polymer Derived from Methacrylamide and Aspartic Acid

Abstract

A new type of thermo- and pH-responsive homopolymer was synthesized using reversible addition−fragmentation chain transfer (RAFT) polymerization. A novel functional methacrylamide monomer bearing α-aspartic acid derivative in the side chain, i.e., N-methacryloyl-l-β-isopropylasparagine benzyl ester (MA-iAsn-OBen), was first synthesized. Three poly(N-methacryloyl-l-β-isopropylasparagine benzyl ester)s [poly(MA-iAsn-OBen)] with controllable molecular weight and narrow molecular weight distribution were then prepared using RAFT polymerization. Selective removal of benzyl groups produced poly(N-methacryloyl-l-β-isopropylasparagine) [poly(MA-iAsn-OH)], which displayed a reversible lower critical solution temperature (LCST) in water. In addition, the LCST can be adjusted from 29 to 60 °C by changing solution pH values, salt concentrations, and polymer molecular weights. Using macromolecular chain transfer agent and RAFT polymerization, we prepared well-defined amphiphilic mPEG45-b-poly(MA-iAsn-OBen)53 diblock copolymer and double hydrophilic block copolymer [mPEG45-b-poly(MA-iAsn-OH)53]. The latter showed a thermo-induced self-assembly in water due to collapse of poly(MA-iAsn-OH) segment. We found that mPEG45-b-poly(MA-iAsn-OH)53 was soluble at room temperature while formed vesicles above the LCST of poly(MA-iAsn-OH)53.