Copper-coordination induced fabrication of stimuli-responsive polymersomes from amphiphilic block copolymer containing pendant thioethers

Abstract

In this work, we synthesized oxidation-responsive amphiphilic block copolymers PEG₄₅-b-P(MET/PBC)_n bearing pendant phenylboronic ester carbamate (PBC) and thioether moieties in the hydrophobic block by RAFT polymerization and post-polymerization modification. As the hydrophobic block length increased, the polymeric self-assemblies underwent a morphological transition from spherical micelles to worm-like micelles to bilayered polymersomes. Triggered by H₂O₂, the polymersomes disintegrated because of the oxidation of thioether to sulfoxides and the decomposition of PBC moieties. Taking advantage of the thioether–copper coordination capability, the hybrid polymersomes with Cu²⁺-cross-linked membrane were fabricated via the co-assembly of the block copolymer with Cu²⁺ ions, driven by the coordination interactions between the hydrophobic block and Cu²⁺ ions. The metal–ligand interaction endows the hybrid polymersomes with a responsive property to the competitive ligand. In the presence of glutathione (GSH) (or sodium ascorbate) and H₂O₂, Cu⁺ ions were in situ produced via the reduction of the entrapped Cu²⁺ ions and subsequently initiated a Fenton-like reaction to generate hydroxyl radicals. The catalytic activity of the hybrid polymersomes-mediated Fenton-like reaction was evaluated by the oxidation of terephthalic acid and the degradation of methylene blue, respectively. In the presence of H₂O₂ and GSH, the hybrid polymersomes underwent a shape change and transformed into a mixture of spherical micelles and worm-like micelles.