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

Graft copolymers containing at 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 (M-n = 5500 to 18 700 g mol(-1), PDI < 1.3), H-1 NMR spectroscopy, and acid/base titrations. The solubility behavior of the graft copolymers ill aqueous media was investigated using turbidity measurements revealing a lower critical Solution temperature (LCST) behavior of the polymers with,I grafting density above 35% The cloud points of the solutions can be varied in a temperature range from 8 to 90 degrees C by adjustment of the polymer composition and the pH of the solution, H-1 NMR measurements in D2O at varying temperatures revealed I collapse of the polymer backbone above the cloud point of the solution whereas parts of the OEtOx side chains remained mobile.