Gelation of Triblock Copolymers in Aqueous Solution through CO2-Triggered Electrostatic Interaction

Polymer systems displaying CO2-triggered rheology alteration are widely investigated in recent years, which can change from nonviscous liquid to high-viscosity solution or even gel by passing CO2 through. Among those polymer systems, a previous study of the group shows that a rationally designed ABA-type triblock copolymer with a hydrophilic middle block and two CO2-responsive end blocks can undergo either gel-sol or sol-gel transition triggered by CO2 as a result of increase or decrease in lower critical solution temperature of A blocks, respectively. This paper describes a new and more flexible approach to achieving CO2-induced gelation of polymer aqueous solution at much lower polymer concentrations. It consists in mixing two water-soluble ABA triblock copolymers that have the same B block but different A blocks: for one polymer, the A blocks are a negatively charged polyelectrolyte, and for the other polymer, the A blocks can be turned positively charged under CO2 stimulation. In this way, CO2 bubbling through an aqueous solution of the two constituent triblock copolymers can induce complexation of the oppositely charged A blocks and, as a result, gelation of the solution of mixed triblock copolymers.