Electrical Response of Poly( N -[3-(dimethylamino)Propyl] Methacrylamide) to CO 2 at a Long Exposure Period.

Amine-functionalized polymers (AFPs) are able to react with carbon dioxide (CO 2 ) and are therefore useful in CO 2 capture and sensing. To develop AFP-based CO 2 sensors, it is critical to examine their electrical responses to CO 2 over long periods of time, so that the device can be used consistently for measuring CO 2 concentration. To this end, we synthesized poly( N -[3-(dimethylamino)propyl] methacrylamide) (pDMAPMAm) by free radical polymerization and tested its ability to behave as a CO 2 -responsive polymer in a transducer. The electrical response of this polymer to CO 2 upon long exposure times was measured in both the aqueous and solid phases. Direct current resistance measurement tests on pDMAPMAm films printed along with the silver electrodes in the presence of CO 2 at various concentrations reveal a two-region electrical response. Upon continuous exposure to different CO 2 flow rates (at a constant pressure of 0.2 MPa), the resistance first decreased over time, reaching a minimum, followed by a gradual increase with further exposure to CO 2 . A similar trend is observed when CO 2 is introduced to an aqueous solution of pDMAPMAm. The in situ monitoring of pH suggests that the change in resistance of pDMAPMAm can be attributed to the protonation of tertiary amine groups in the presence of CO 2 . This two-region response of pDMAPMAm is based on a proton-hopping mechanism and a change in the number of free amines when pDMAPMAm is exposed to various levels of CO 2 .