Dual Responsive Methacrylic Acid and Oligo(2-ethyl-2-oxazoline) Containing Graft Copolymers

Graft copolymers containing a poly(methacrylic acid) (PMAA) backbone and oligo(2-ethyl-2-oxazoline) (OEtOx) side chains were synthesized by reversible addition−fragmentation chain transfer (RAFT) polymerization of methacrylic acid (MAA) and OEtOx methacrylate macromonomers. In order to achieve a constant backbone length of the graft copolymer, living OEtOx chains were also directly grafted onto a deprotonated PMAA backbone in grafting densities from 7% to 92%. Both methods resulted in graft copolymers which were characterized by SEC (Mn = 5500 to 18 700 g mol−1, PDI < 1.3), 1H NMR spectroscopy, and acid/base titrations. The solubility behavior of the graft copolymers in aqueous media was investigated using turbidity measurements revealing a lower critical solution temperature (LCST) behavior of the polymers with a grafting density above 35%. The cloud points of the solutions can be varied in a temperature range from 8 to 90 °C by adjustment of the polymer composition and the pH of the solution. 1H NMR measurements in D2O at varying temperatures revealed a collapse of the polymer backbone above the cloud point of the solution whereas parts of the OEtOx side chains remained mobile.