Crystallization vs Metal Chelation: Solution Self-Assembly of Dual Responsive Block Copolymers

We herein report the synthesis and characterization of dual stimuli-responsive poly(2-iso-propyl-2-oxazoline)-block-poly(2-acrylamido glycolic acid) (PiPrOx-b-PAGA) double hydrophilic block copolymers (BCPs) by an effective combination of ring-opening and reversible addition-fragmentation chain transfer (RAFT) polymerization. The resulting materials are responsive toward several external triggers: (1) the PiPrOx segment undergoes a coil-to-globule transition upon heating above the cloud point temperature (TCP), (2) the PAGA block chelates M2+ metal ions and provides straightforward access to nanostructured hybrid materials, and (3) prolonged heating above the T-CP for PiPrOx enables crystallization-driven solution self-assembly (CDSA) toward anisotropic micelles and superstructures. We are further able to show that the cloud point temperature (T-CP) of PiPrOx-b-PAGA micelles can be tuned from similar to 30 to 68 degrees C by varying either the BCP composition (PiPrOx to PAGA ratio) or by the amount of metal ions being present. The different aggregates were characterized by transmission electron microscopy (TEM), wide-angle X-ray scattering (WAXS), and dynamic light scattering (DLS). Our results indicate that micellar size, shape, and T-CP are closely connected to BCP composition and the nature of chelated metal ions. In our opinion, such inorganic-organic hybrid materials are of interest with regard to (photo)catalysis, as sensors, or as potential drug delivery systems.