Anchoring high-density cooperative catalytic sites within triethylenediamine-based ionic-liquid polymers via microenvironment modulation for efficient CO2 fixation

Abstract

The precise microenvironment modulation of ionic sites to promote the catalytic performances of ionic-liquid polymers for CO2 transformation has been highly attractive but rarely attempted. Herein, we reported a strategy to synthesize the triethylenediamine-derived ionic-liquid polymer (PDD-S) featured with branched structure and high site density (4.10 mmol·g−1). In distinct with the conventional synthetic routes, this method involved the pre-grafting and subsequent self-polymerization of ionic monomer, which suppressed the competitive reactions and broke the limitations of precursor selection, while ensuring the high content and even distribution of ionic sites within the polymeric framework. Furthermore, during CO2 cycloaddition with epoxides we showed that these unique structural features allowed the adequate exposure of active sites under the dual effects of steric hindrance and charge repulsion. The PDD-S exhibited noteworthy catalytic performance, with a carbonate yield of 97.3 %, under the moderate conditions (100 °C, 4 h, 1 MPa) in the absence of any metal, co-catalyst, or solvent. Additionally, the desirable reusability, epoxide universality, and structural stability were also attained. The experiments combining with the activation energy and DFT theoretical calculations, attributed the synergistic interplay of tertiary N, quaternary ammonium, and Cl- anions to the acceleration of ring-opening process, thereby promoting the CO2 transformation. The newly developed approach offers one perspective to the controllable fabrication of ionic-liquid polymers for catalytic fixation of CO2.