Transitioning from Photoinitiation to Thermal Initiation in RAFT Dispersion Polymerization via a Small Modification of the Macro-RAFT Agent: A Scalable Approach for Monodisperse Surface-Functional Polymeric Microspheres

Monodisperse surface-functional polymeric microspheres prepared by the photoinitiated reversible addition–fragmentation chain transfer (RAFT) dispersion polymerization offer promising potential for diverse applications due to their high uniformity, size tunability, and variable coronal and core chemistries. However, this method strongly relies on the unique characteristics of photoinitiation, which hinders scale-up and the preparation of functional microspheres (e.g., colored microspheres). Here, we demonstrate a successful transition from photoinitiation to thermal initiation in RAFT dispersion polymerization via the chain extension of a short solvophobic block to the macro-RAFT agent to access monodisperse surface-functional polymeric microspheres. Mechanistic insights into the polymerization process were provided, demonstrating the importance of the solvophobic block in the formation of monodisperse polymeric microspheres. It was found that the solvophobic block not only enhances the anchoring ability of the stabilizer toward particles but also promotes nucleation. Furthermore, thermally initiated RAFT dispersion polymerization can be employed to access scalable, monodisperse, size-tunable, and molecular-weight-tunable polymeric microspheres with diverse surface functionality. Significantly, thermally initiated RAFT dispersion polymerization becomes robust to the presence of functional species, allowing the one-step preparation of cross-linked, surface-functional polymeric microspheres with high uniformity. This approach to monodisperse surface-functional polymeric microspheres overcomes the complications of photoinitiation to facilitate eventual scale-up as well as the preparation of functional polymeric microspheres for some specific applications.