CO₂-switchable behavior of chitosan-g-poly[(2-dimethylamino)ethyl methacrylate] as an emulsifier

Chitosan-g-poly[(2-dimethylamino)ethyl methacrylate] was investigated as a CO₂-switchable emulsifier in this study. Poly(2-dimethylamino)ethyl methacrylate (PDMAEMA) was prepared by atom transfer radical polymerization followed by grafting to chitosan (CS). The CO₂-responsiveness and reversible CO₂-switchable temperature- and pH-sensitive behavior of PDMAEMA and CS-g-PDMAEMA were investigated as emulsifiers via simple CO₂ and N₂ bubbling. The lower critical solution temperatures (LCSTs) of PDMAEMA and CS-g-PDMAEMA aqueous solutions both increased as pH decreased to about pH 7.3, at which point the LCSTs disappeared. At elevated temperatures (e.g. 60°C), CO₂ bubbling removed the turbidity in CS-g-PDMAEMA aqueous solution and N₂ bubbling restored turbidity. The presence of CS-g-PDMAEMA in a two-phase solution of n-butanol/deionized water enabled the formation of a completely emulsified single phase after CO₂ bubbling, which reverted to a two-phase solution on N₂ bubbling. Overall, CS-g-PDMAEMA has potential as a CO₂-switchable emulsifier.