Thermo- and pH-Responsive Association Behavior of Dual Hydrophilic Graft Chitosan Terpolymer Synthesized via ATRP and Click Chemistry

Abstract

A comb-like dual hydrophilic graft chitosan terpolymer, chitosan grafted with both poly[(2-dimethylamino)ethyl methacrylate] and poly(N-isopropylacrylamide) or, simply, CS(-g-PDMAEMA)-g-PNIPAM, was synthesized by means of atom transfer radical polymerization (ATRP) and click chemistry. At first, PDMAEMA and PNIPAM were synthesized via ATRP, followed by substituting the halide end groups with azido groups. After converting CS into alkynyl-CS via amidation, PDMAEMA-N3 and PNIPAM-N3 side chains were successfully grafted onto the CS backbone via click reaction, leading to the well-defined graft terpolymer. Thermo- and pH-responsive micellization behavior of the graft terpolymer in aqueous solutions was investigated by proton nuclear magnetic resonance (1H NMR), laser light scattering (LLS), surface tensiometry, zeta potential, and transmission electron microscopy (TEM). The core−shell structured micelles with PNIAPM as a core and CS/PDMAEMA as a shell were formed in acidic environment (pH < 4) at elevated temperature (>38 °C), whereas the unimers turned into the micelles with CS/PDMAEMA cores in alkaline solutions (pH > 7) at room temperature.