Rigid Ladder-Type Porous Polymer Networks for Entropically Favorable Gas Adsorption

To improve methane storage capacity of porous organic materials, this work demonstrates that a rigid ladder-type backbone is more entropically favorable for gas adsorption and leads to a high gas uptake per unit surface area. A porous ladder polymer network was designed and synthesized as the model material via cross-coupling polymerization and subsequent ring-closing olefin metathesis, followed by characterization by solid-state nuclear magnetic resonance (NMR) spectroscopy. This material exhibited a remarkable methane uptake per unit surface area, which outperformed those of most reported porous organic materials. Variable-temperature thermodynamic adsorption measurements corroborated the significantly less negative entropy penalty during high-pressure gas adsorption, compared to its non-ladder-type counterpart. This method provides an orthogonal strategy for multiplying volumetric methane uptake capacity of porous materials. The entropic approach also offers the opportunity to increase deliverable gas upon pressure change while mitigating the performance decline in high-temperature applications.