Polymerization-Induced Interfacial Self-Assembly: A Powerful Tool for the Synthesis of Micro-sized Hollow Capsules

Synthesis of hollow capsules by the polymerization-induced interfacial self-assembly (PIISA) approach is reported in this research. In a typical PIISA process, a hydrophilic polymer synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization is used as macro-CTA, toluene droplets in water are used as templates, and methyl methacrylate (MMA) is used as a monomer. Because of the insolubility in toluene, the initial chain extension of macro-CTA with MMA is performed in water. With an increase in PMMA block length, the formed block copolymer (BCP) chains migrate to the liquid–liquid interface with hydrophilic blocks in the aqueous phase and PMMA blocks in the oil phase, so that the interfacial tension is reduced. Because the concentration of MMA in the aqueous phase is lower than that in the oil phase, the interfacial RAFT polymerization of MMA exhibits an improved polymerization rate, as compared to the polymerization in the aqueous phase. Upon the addition of a cross-linker, cross-linked hollow capsules are synthesized. The average size of the cross-linked capsules decreases with an increase in the cross-linker content. It is demonstrated that inorganic particles and organic compounds can be encapsulated in the voids of the capsules. PIISA is a process combining chain extension and interface-directed self-assembly of BCP chains, and it is reasonable to expect that this approach will find applications in the synthesis of amphiphilic BCPs, colloidal particles, and drug carriers.