Multistimuli-Responsive Emulsifiers Based on Two-WayAmphiphilic Diblock Polymers

Diblock copolymers of poly­(tert-butyl methacrylate) (PtBuMA) 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 PtBuMA 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 CO2-switchable emulsifiers for emulsification/demulsification of n-octane (an oil) in water in response to CO2/N2 bubbling. The amphiphilicity of PtBuMA-b-PDMAEMA was switched on, and the amphiphilicity of PMAA-b-PDMAEMA was switched off by CO2 bubbling at pH 12 and 25 °C to achieve emulsification/demulsification. A longer PDMAEMA block length in PMAA-b-PDMAEMA conferred more sensitive CO2-responsive amphiphilicity but reduced the extent of recovery of emulsification ability on N2 bubbling. This newly developed diblock copolymer system could potentially serve as a “multifunctional surfactant” for CO2-switchable emulsification/demulsification of oil-in-water and water-in-oil mixtures.