Efficient thiazole-based polyimines as selective and reversible chemical absorbents for CO₂ capture and separation: Synthesis, characterization and application

A new series of polyimines (PIMs-1-9) including ortho-linked thiazole units and flexible thioether linkages were synthesized from diamine monomers (DA-1-3) and some commercially available aromatic dialdehydes (terephthalaldehyde, isophthalaldehyde and 2,5-thiophenedicarboxaldehyde) via Schiff-base condensation reaction. The synthesized polymers as amorphous solids were obtained with high efficiency (74–89%), inherent viscosities in the range of 0.98–1.33 dL g⁻¹ in DMF and high solubility in aprotic polar solvents (DMSO, DMAc, DMF, NMP, and Py). The PIMs were characterized via viscosimetry, elemental analysis, FT-IR spectroscopy, X-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). High thermal resistance revealed for PIMs as glass transition temperatures (T_gs) ranging in 104–189 °C along with 10% weight loss temperatures exceeding 268–390 °C in air and 310–430 °C in nitrogen atmosphere. The polymers were examined for CO₂ absorption at 298 K as well as 318 K and high absorption capacity exhibited (maximum 3.72 mmol/g or 163.68 mg/g at 1 bar and 298 K for PIM-4) after 2 h and desorption at 373 K under vacuum conditions (100 mbar) in 20 min. More importantly, remarkable ideal selectivity ratios of CO₂/N₂ (77.3) and CO₂/CH₄ (13.7) at 1 bar and 298 K were obtained and recyclability of PIM-4 for CO₂ capturing was determined without considerable loss of gas absorption.