Abstract
Hydroxyl-functional amidines provide a single-component platform in which CO 2 fixation generates ionic functionality and promotes intermolecular organization. Here, structurally related amidines derived from serinol and isoserinol were compared as precursors of CO 2 -responsive polymeric ionic liquids (PILs). Direct treatment of the neat amidines with CO 2 resulted in the formation of CO 2 -derived ionic structures consistent with amidinium–alkyl carbonate units and their subsequent intermolecular association. Time-resolved 1 H NMR and FTIR spectroscopy showed progressive development of the CO 2 -derived ionic state, while 13 C NMR supported the presence of alkyl carbonate and protonated amidinium carbon environments. The two systems exhibited distinct transformation profiles. Isoserinol-derived PIL-2 showed a faster initial spectroscopic response, a more rapid change in the local microenvironment detected by pyrene fluorescence, and earlier stabilization of relative viscosity. GPC indicated a greater contribution of higher apparent molecular-size species in PIL-2, consistent with more pronounced intermolecular association. After 60 min, Amidine-2 captured 2.43 mmol g −1 CO 2 , compared with 1.63 mmol g −1 for Amidine-1. Principal component analysis further distinguished the systems based on their spectroscopic and physicochemical responses. DFT calculations showed that Amidine-2 has a higher molecular dipole moment and a shorter OH···N separation involving the secondary hydroxyl group, providing a molecular basis for its stronger response to CO 2 . These results indicate that the relative arrangement of hydroxyl and amidine functionalities influences both CO 2 fixation and the association of the resulting CO 2 -derived ionic units into extended structures.