Abstract: This article strategy for nanoencapsulation via interfacially confined controlled/living radical miniemulsion polymerization which is stabilized by (pS-b-pAA)RAFT without emulsifiers was proposed. The principle of the strategy is based on the self-assembly of amphiphilic molecules and reversible addition fragmentation transfer (RAFT) radical polymerization chemistry. The RAFT agent was designed to be amphiphilic and was used as a stabilizer of the miniemulsion. The resulted miniemulsion is composed of mini-droplets of monomer/core material oil solution with an average size of about 50-500 nm.The RAFT molecules are confined at the interface of water/oil. When a initiator is added, primary radicals are born. After several additions of monomer, the radicals become surface active and enter the mini-droplets. As the RAFT agent is has very high chain transfer coefficient, the radical would transfer among the RAFT agents located at the interface of the oil/water. By this way, the radical remains to be anchored in the interface, so the polymerization is confined in the interface. The polymer chains then grow inwards gradually, leading to the formation of a polymer shell.
Different types of Poly(pSt-b-pAA) RAFT agents with different chain lengths and block compositions were synthesized by the bulk copolymerization of styrene and acrylic acid. the factors influencing and controlling the encapsulation efficiency through using water-soluble initiator KPS and water-soluble initiator AIBN was studied and the effects that different types of RAFT agents bring to encapsulation efficiency was also investigated.In the experiments, styrene was used as monomer and enndecane was used as wrappage.
Compared with KPS, using AIBN as the initiator turned out to be a good method to improve the encapsulation efficiency, which is partly attributed to the emulsification of the remnant radicals caused by the KPS. At the same time, when the RAFT agents have a good ability of emulsification, the encapsulation efficiency can be improved.
Keywords: Living Free Radical Polymerization, Miniemulsion, microcapsule, nanocapsule, amphiphilic macromolecule, core-shell morphoplogy