Synthesis of Gemini-Like Methyl Acrylate-Acrylic Acid-Methyl Acrylate Triblock Copolymers Surfactants by RAFT Polymerization in Solution and Investigation of their Behavior at the Air–Water Interface

A series of methyl acrylate-acrylic acid amphiphilic triblock copolymers (PMA-PAA-PMA) were prepared by solution polymerization using S,S′-bis (α,α-dimethy1acetic acid) trithiocarbonate (BDAT) as a reversible addition fragmentation chain transfer (RAFT) agent and methyl acrylate (MA) as the first monomer. The triblock copolymers and their common MA homopolymer precursors were characterized in terms of their compositions, molecular weights and behavior at the air–water interface using 1H-NMR spectroscopy, thermogravimetric analysis, gel permeation chromatography, surface tension, transmission electron microscopy (TEM) and dynamic light scattering respectively. The results indicated that PMA-PAA-PMA was successfully synthesized through RAFT polymerization. The polydispersity index (PDI) decreased when the molar ratio [n(MA)/n(AA)] increased, the lowest PDI was obtained at 5.23 wt% RAFT and the molecular weights were consistent with the theoretical value as the RAFT agent percentage varied. The polymer neutralized by sodium hydroxide solution shows a low critical micelle concentration (CMC), which was <10−2 mol L−1 in water. The A min values increased and showed a maximum with decreased AA chain length. TEM showed that the neutralized polymer formed a special vesicle structure with large pore structure which led to a low CMC and surface tension of water.