Porosity Engineering of Hyper-Cross-Linked Polymers Based on Fine-Tuned Rigidity in Building Blocks and High-Pressure Methane Storage Applications

Exploring the effect of the structural rigidity of selected building blocks on the resultant porosity of the desired polymers is crucial for the bottom-up design of hyper-cross-linked polymers. Herein, several novel polymers, based on two series building blocks with stepwise fine-tuned rigidity, were constructed by the low-cost solvent knitting method. Significantly, the porosity of these polymers is highly consistent with the structural rigidity of the basic building blocks, dramatically enhanced from a poor porous state to a micropore-rich framework, with an increase in BET surface areas from 248 to 1276 m2 g-1 for the HCPs based on monomers containing double benzene rings and from 37 to 2368 m2 g-1 for tetraphenyl-like monomer-based HCPs. The best performances, especially concerning methane adsorption capacity, are reached for the rigid 9,9 '-spirobifluorene (SBF)-based HCP-SBF framework and flexible tetraphenylmethane (TPM)-based HCP-TPM, showing a 5-100 bar working capacity of 206 cm3 (STP: 273 K, 1 atm) cm-3 (0.296 g g-1) and 199 cm3 (STP) cm-3 (0.112 g g-1) at 273 K, respectively. The bottom-up-designed HCPs with engineered porosity are expected to become novel candidates for onboard methane storage.