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

Abstract

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 TCP 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 (TCP) of PiPrOx-b-PAGA micelles can be tuned from ∼30 to 68 °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 TCP 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.