High-Temperature Photoinitiated RAFT Dispersion Polymerization: A Light-Mediated Approach for Controlled Synthesis of Well-Defined Polymeric Microspheres

Monodisperse polymeric microspheres (uniform spherical aggregates of polymer chains with micrometer-scale dimensions) hold great promise for applications spanning materials science, biotechnology, and diagnostics. Yet, achieving simultaneous control over polymer chain growth and microsphere formation remains a formidable challenge. Here, we report a high-temperature photoinitiated reversible addition–fragmentation chain transfer (RAFT) dispersion polymerization that employs a poly(ethylene glycol)-based macro-RAFT agent to direct microsphere formation and a small-molecule RAFT agent to mediate polymer chain growth within the particles. This dual-RAFT strategy enables the synthesis of polymeric microspheres with narrow size distributions and well-defined polymers of tunable molecular weights, while the stabilizer loading can be as little as 0.1 wt %. Both polymer chain and particle growth can be temporally modulated by light on/off switching. The resulting polymers retain high end-group fidelity, allowing efficient one-pot synthesis of well-defined (multi)block copolymers with low dispersities while maintaining particle size uniformity. Furthermore, this approach provides access to nanostructured block copolymer microspheres with uniform sizes and well-defined internal morphologies, an achievement that remains elusive by conventional methods.