Multistimuli-Responsive Emulsifiers Based on Two-Way Amphiphilic Diblock Polymers

Diblock copolymers of poly( tert -butyl methacrylate) (P t BuMA) and poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) of four different block lengths were prepared by sequential two-step reversible addition-fragmentation chain transfer radical polymerization, followed by hydrolysis of the P t BuMA blocks to obtain poly(methacrylic acid)- b -PDMAEMA (PMAA -b- PDMAEMA). The effect of the PDMAEMA block length on the multistimuli-responsive amphiphilic features of both types of diblock copolymers was investigated as CO 2 -switchable emulsifiers for emulsification/demulsification of n -octane (an oil) in water in response to CO 2 /N 2 bubbling. The amphiphilicity of P t BuMA -b- PDMAEMA was switched on, and the amphiphilicity of PMAA -b- PDMAEMA was switched off by CO 2 bubbling at pH 12 and 25 °C to achieve emulsification/demulsification. A longer PDMAEMA block length in PMAA -b- PDMAEMA conferred more sensitive CO 2 -responsive amphiphilicity but reduced the extent of recovery of emulsification ability on N 2 bubbling. This newly developed diblock copolymer system could potentially serve as a "multifunctional surfactant" for CO 2 -switchable emulsification/demulsification of oil-in-water and water-in-oil mixtures.