Microporous Polybenzoxazoles with Tunable Porosity and Heteroatom Concentration for Dynamic Adsorption/Separation of CO2 Mixed Gases

Three hyper-cross-linked microporous polybenzoxazoles (PBO-M, PBO-Ad, and PBO-Si) with uniform pores are synthesized through "one-pot" condensation polymerizations from 3,3′-diamino-4,4′-dihydroxybiphenyl with tetrakis(4-formylphenyl)methane, 1,3,5,7-tetrakis(4-formyphenyl)adamantane, and tetrakis(4-formylphenyl)silane, respectively. Their porosity parameters and chemical compositions, such as microporous sizes (0.98–1.46 nm), ratios of microporous volume to total porous volume (0.36–0.53), ratios of O/C (0.156–0.195), and N/C (0.079–0.095), are finely tunable. The adsorption properties of CO2, N2, and CH4 measured through the static adsorption isotherms of single-component gases and dynamic breakthrough curves are comparatively studied. Among the three polymers, PBO-M possesses the smallest pore size and the highest concentrations of heteroatoms, and consequently shows the largest CO2 adsorption capacity (11.6 wt %, 273 K/1 bar) and highest separation factors of CO2/N2 (96.6) and CO2/CH4 (12.4). The results are interpreted in terms of the porous structure, isosteric enthalpies of adsorption, and the physicochemical parameters of polymer skeletons and gases in detail.