A macroinitiator PEG6000-Br, was synthesized by esterification reaction of PEG6000 and α-Bromoisobutyryl bromide. By using ATRP method, a symmetrical triblock polymer with the same degree of polymerization, poly(2-(Dimethylamino)ethyl methacrylate)-PEG-poly(2-(Dimethylamino)ethyl methacrylate) (PDM165-PEG165-PDM165), was synthesized. The structures were characterized by FT IR and 1H NMR. The CO2/N2 switchability was proved by pH and conductivity, after 5 min of bubbling CO2, pH decreased from 7.74 to 5.47 and the conductivity increased from 0.176 mS/cm to 0.405 mS/cm rapidly. Then, after 30 min of bubbling N2, the pH recovered to the initial 7.74 and the conductivity decreased to the initial value of 0.177 mS/cm smoothly. The self-assembled unilamellar vesicles-network transition was observed by cryo-TEM, thus result in enhancement of viscosity increase from 3 mPa•s to 12 mPa•s. The key mechanism of these changes is protonation of tertiary amine groups in PDM blocks and was proved by 1H NMR, the chemical shifts of H near N atom downfield from 2.3, 2.7, 4.1 ppm to 2.8, 3.2, 4.3 ppm, respectively.