Dual-Stimuli-Responsive Block Copolymers Derived from Proline Derivatives

Novel pH-and thereto-responsive block copolymers comprising proline-based segments were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. Poly(N-acryloyl-L-proline methyl ester), poly(A-Pro-OMe), was selected as a thereto-responsive segment, whereas poly(N-acryloyl-L-proline), poly(A-Pro-OH), was employed as a weak anionic polyelectrolyte. The chain extension from the dithiocarbamate-terminated poly(A-Pro-OH) to A-Pro-OMe could be well controlled under suitable conditions, and it provided block copolymers with as-designed chain structures and low polydispersities. The characteristic pH- and thereto-responsive properties of the block copolymers were then investigated in aqueous solutions. By varying the pH, salt concentration, and comonomer composition, the lower critical solution temperature (LCST) can be tuned between 18 and 55 degrees C. The chiroptical properties and assembled structures of the resulting block copolymers in aqueous solutions were evaluated by circular dichroism (CD) and dynamic light scattering (DLS) measurements.