Photo-Triggered Disassembly of Phosphorylcholine-Based pH-Responsive Block Copolymer Micelles via Encapsulated Photoacid Generators

We propose a strategy to trigger micelle disassembly upon light irradiation by encapsulating a photoacid generator (PAG) within pH-responsive polymer micelles. A diblock copolymer composed of hydrophilic, biocompatible poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC) and pH-responsive poly(2-(diethylamino)ethyl methacrylate) (PDEA), denoted as PMPC-b-PDEA (M₁₀₀D₉₆), was synthesized via reversible addition-fragmentation chain-transfer (RAFT) polymerization. Under acidic conditions, the pendant tertiary amine groups in the PDEA block are protonated, rendering the PDEA block hydrophilic; consequently, M₁₀₀D₉₆ dissolves in water as unimers. In contrast, under basic conditions, the PDEA block becomes deprotonated and hydrophobic, leading to the formation of core-shell spherical micelles with a PDEA core and PMPC shell. A hydrophobic PAG was encapsulated within the hydrophobic micelle core. Aqueous solutions of the PAG-loaded micelles were irradiated with UV light, and photodecomposition of PAG was confirmed by UV-vis absorption spectroscopy. The acid generated from PAG induced protonation of the tertiary amine groups in the PDEA block and possibly induced partial hydrolysis of the pendant ester groups, increasing the overall hydrophilicity and inducing micelle disassembly. Dynamic light scattering and zeta potential measurements further confirmed the disassembly of the micelles upon light irradiation. Furthermore, when both PAG and a hydrophobic guest molecule, coumarin 6 (C6), were simultaneously encapsulated in the M₁₀₀D₉₆ micelles, controlled release of C6 was achieved upon light-induced disassembly of the micelles.