Synthesis and emulsifying performance of polyester sodium olefin sulfonate polymer as a CO₂-switchable surfactant

Polymer surfactants are widely used in scientific research and industrial fields such as food, agriculture and spanning. In order to reduce the side effect caused by the residual of the inactive polymer after most of the practical application process, designing and developing switchable polymer surfactants is of great significance and application value. A CO₂-switchable surfactant Poly(N, N-Diethylaminoethyl methacrylate-sodium vinylsulfonate) (P(DEAEMA-SVS)) has been synthesized by free radical polymerization. The structure and molecular weight distribution of P(DEAEMA-SVS) were characterized by ¹H-NMR and GPC spectra. The stability of P(DEAEMA-SVS) emulsion was studied by the surface tension and interfacial tension. The polymer P(DEAEMA-SVS) with the size of about 113 nm and the narrow particle size distribution form via N, N-Diethylaminoethyl methacrylate (DEAEMA) and sodium vinylsulfonate (SVS) of 1∶1 mole ratio as reaction monomers, which decrease the surface tension of water to 37.279 mN/m and the interfacial tension of water/paraffin wax to 5.492 mN/m. It is indicated that P(DEAEMA-SVS) polymer is an effective CO₂-switchable O/W surfactant to stabilize emulsion as a only emulsifier. The surface activity and CO₂ response of the polymer were evaluated by mixing the aqueous solution (1wt%) with paraffin wax. Bubbling CO₂ for 30 min to the milky emulsion, it turns into clear and bubbling N₂ for 30 min at 60℃, and converts to its original state, showing excellent cyclic performance of de-emulsification and re-emulsification process. The research results of emulsification mechanism show that the side-electron mobility and photogenerated electron-hole pairs separation. Chained tertiary amino groups of P(DEAEMA-SVS) polymer protonize and turn into hydrophilic quatemary ammonium salt to destroy the oil/water balance of the emulsion with bubbling CO₂, while quatemary ammonium salt deprotonizes and returns into hydrophobic tertiary aminogroups with bubbling N₂ at 60℃.