In situ cross-linking in RAFT-mediated emulsion polymerization: Reshaping the preparation of cross-linked block copolymer nano-objects by polymerization-induced self-assembly

Abstract

Large-scale preparation of cross-linked block copolymer nano-objects using polymerization-induced self-assembly (PISA) generally suffers from the limitation that high degrees of cross-linking in the early stage must be avoided. Herein, we demonstrate that the intrinsic monomer-feeding mechanism of reversible addition-fragmentation chain transfer (RAFT)-mediated emulsion polymerization can be used to delay in situ cross-linking during PISA, allowing the preparation of cross-linked block copolymer nano-objects with high cross-linker contents. When using hydrophobic cross-linkers, the cross-linker along with monomer diffuses from monomer droplets to micelles gradually. When using hydrophilic cross-linkers, the cross-linker is prone to stay in water rather than diffuse into hydrophobic micellar cores. 1H NMR analysis confirmed the consumption behavior of cross-linkers during RAFT-mediated emulsion polymerization regardless of cross-linkers used. A variety of cross-linkers with different aqueous solubilities, symmetries, and functional groups were employed to prepare cross-linked block copolymer nano-objects. It is demonstrated that increasing the content of cross-linker promoted the formation of higher-order morphologies. We expect this study will not only expand the scope of RAFT-mediated PISA for in situ preparation of cross-linked block copolymer nano-objects, but also inspires researchers in this field to prepare novel polymer nanoparticles based on the unique mechanism of RAFT-mediated emulsion polymerization.