From RAFT emulsion polymerization to RAFT dispersion polymerization: a facile approach to tuning dispersities and behaviors of self-assembled block copolymers

Heterogeneous reversible addition–fragmentation chain transfer (RAFT) polymerization coupled with polymerization-induced self-assembly (PISA) can be performed through either RAFT emulsion polymerization or RAFT dispersion polymerization, providing opportunities for the synthesis of block copolymers with low dispersities and polymer nanoparticles with various morphologies. In this study, we have demonstrated the successful transition from photoinitiated RAFT emulsion polymerization to photoinitiated RAFT dispersion polymerization by solely changing the solvent composition from water to water/ethanol. Kinetic studies indicated that slower polymerization was observed with higher ethanol content. Size exclusion chromatography (SEC) analysis demonstrated that narrower molecular weight distributions were achieved on increasing the ethanol content due to faster radical diffusion within the micellar core. The dispersity of block copolymers can be changed by varying the ethanol content used in photoinitiated heterogeneous RAFT polymerization. Moreover, the reaction temperature has also been explored as a parameter to control the diffusion of radicals within the micellar core and therefore dispersities of block copolymers. Finally, the morphological evolution of block copolymer nanoparticles during the transition from RAFT emulsion polymerization to RAFT dispersion polymerization was also investigated. The present study is anticipated to significantly expand the scope of heterogeneous RAFT polymerization by allowing access to a wide range of block copolymers with different dispersities and polymer nanoparticles with diverse morphologies.