A “green” method for preparing ABCBA penta-block elastomers by using RAFT emulsion polymerization

A clean method for preparing ABCBA penta-block terpolymers was developed in a surfactant and organic solvent free emulsion system via one-pot RAFT polymerization. The prepared ABCBA penta-block terpolymers show large fracture tensile strain, low permanent set and potential application as elastomer materials. During the preparation process, polyacrylic acid (PAA) was firstly synthesized as the A block via RAFT polymerization in water in the presence of a dual-functional RAFT agent. Subsequently, we selected a partially water-soluble monomer 2,2,2-trifluoroethyl acrylate (TFEA) to synthesize the B block, and ABA tri-block copolymers could be obtained via organic solvent free RAFT emulsion polymerization. Using the ABA tri-block copolymers as a surfactant, the ABCBA penta-block terpolymers were further synthesized using 2,2,3,4,4,4-hexafluorobutyl acrylate (HFBA) as the third monomer in an organic solvent free system. It has been found that the emulsification efficiency of the ABA tri-block copolymers is higher than that of the corresponding AB di-block copolymers. The assembly mechanism of penta-block terpolymers to form a tri-layer core–shell latex particle was proposed and confirmed by TEM images. Finally, we obtained a transparent and hydrophobic elastomeric film by directly casting the synthesized penta-block terpolymer latexes and subsequent heat treatment. The films have excellent mechanical properties and water resistance.