CO2-Responsive Polymers. Part I. Fundamental Concepts and Classification

Stimuli-responsive systems, which have the ability to respond to external or internal stimuli through transition behaviors, constitute the most exciting scientific areas of smart materials. In recent years, the use of carbon dioxide (CO2), as a trigger in smart systems, has received great attention because it is inexpensive, available and abundant in nature. Some of various CO2-responsive materials include polymers, latexes, solvents, solutes, gels, surfactants, and catalysts. CO2-responsive materials reveal a reversible transition state (from neutral to charge state and vice versa) in response to environmental changes. The most important feature of these systems is that, during these transitions CO2 does not accumulate in a system upon repeated cycles. To have CO2-responsiveness in systems, CO2-responsive moieties are required in the structure of materials; these moieties can be a surfactant, monomer, initiator or solvent. Therefore, in this review, we start from recalling the chemical concepts of the CO2-responsive functional groups as well as presenting the fundamental principles of CO2-responsivity. Since, among the CO2-responsive materials that have been developed, polymer-based materials are of particular interest, in continue, we have provided some examples of systems including CO2-responsive polymers.