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

Diblock copolymers of poly(-butyl methacrylate) (PBuMA) 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 PBuMA blocks to obtain poly(methacrylic acid)--PDMAEMA (PMAAPDMAEMA). The effect of the PDMAEMA block length on the multistimuli-responsive amphiphilic features of both types of diblock copolymers was investigated as CO-switchable emulsifiers for emulsification/demulsification of -octane (an oil) in water in response to CO/N bubbling. The amphiphilicity of PBuMAPDMAEMA was switched on, and the amphiphilicity of PMAAPDMAEMA was switched off by CO bubbling at pH 12 and 25 °C to achieve emulsification/demulsification. A longer PDMAEMA block length in PMAAPDMAEMA conferred more sensitive CO-responsive amphiphilicity but reduced the extent of recovery of emulsification ability on N bubbling. This newly developed diblock copolymer system could potentially serve as a "multifunctional surfactant" for CO-switchable emulsification/demulsification of oil-in-water and water-in-oil mixtures.