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 (ter-ephthalaldehyde, 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(g)s) ranging in 104-189 degrees C along with 10% weight loss temperatures exceeding 268-390 degrees C in air and 310-430 degrees 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/N-2 (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.