The polymer residues after CO2-mediated desalination can be regenerated using a strong base (aq. NaOH solution, 0.1 N) and subjected to the next round of CO2-mediated desalination with aq. NaCl solution (Figure ). This PEI-C16 regeneration and recycling was repeated thrice and monitored for structural variations using PXRD and peak analyses. A slight broadening of diffraction peaks was observed after the first desalination in the PXRD data of PEI-C16-Cl (Figure ). However, all stages of regeneration (after base and acid treatment) revealed no significant broadening in the three regenerated residues compared to PEI-C16*. A similar trend was observed in the residue after the first regeneration cycle, where the crystallinity degree of PEI-C16-Regen (19.8%) was similar to that of PEI-C16* (19.6%). After the second and third regeneration steps, we observed a slight decrease in crystallinity to 17.7% and 17.2%, respectively (Figure ). Despite these subtle variations in crystalline content, alkylated PEI showed consistent chloride removal performance across multiple regeneration cycles (Figure ). Also, TGA and NMR spectroscopy confirmed that the structural and molecular integrity of the polymer remained intact (Figures and), highlighting the significant role of alkylation in sample recovery without compromising the desalination performance.