CO2‐switchable polymeric vesicle‐network structure transition induced by a hairpin‐line molecular configuration conversion

A triblock copolymer, containing a polyethylene glycol (PEG) block and two symmetrical poly(2‐(dimethylamino)ethyl methacrylate) (PDM) blocks, was synthesized by using PEG‐based macroinitiator with copper‐mediated living radical polymerization. The conductivity tests showed that the copolymer exhibited switchable responsiveness to CO₂, i.e., a relatively high conductivity of solution can be switched on and off by bubbling and removing of CO₂. According to the nuclear magnetic resonance results, the CO₂‐switchable conductivity variation could be attributed to protonation and deprotonation of tertiary amine groups in PDM blocks. Moreover, at a proper weight concentration 0.5%, the copolymer aqueous solution displayed a CO₂‐switchable viscosity variation. Scanning electron microscopy, cryogenic transmission electron microscopy, and dynamic light scattering characterization jointly demonstrated that the viscosity variation was the result of a CO₂‐switchable vesicle‐network aggregate structure transition. This structure transition can actually be attributed to a hairpin‐line molecular configuration conversion in terms of the reasonable mechanism discussion. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44417.