Effect of cross-link density on carbon dioxide separation in polydimethylsiloxane-norbornene membranes

The development of high-performance materials for carbon dioxide separation and capture will significantly contribute to a solution for climate change. Herein, (bicycloheptenyl)ethyl-terminated polydimethylsiloxane (PDMSPNB) membranes with varied cross-link densities were synthesized via ring-opening metathesis polymerization. The developed polymer membranes show higher permeability and better selectivity than those of conventional cross-linked PDMS membrane. The achieved performance (CO₂ permeability≈6800 Barrer; CO₂/N₂ selectivity≈14) is very promising for practical applications. The key to achieving this high performance is the use of an in situ cross-linking method for difunctional PDMS macromonomers, which provides lightly cross-linked membranes. By combining positron annihilation lifetime spectroscopy, broadband dielectric spectroscopy, and gas solubility measurements, key parameters necessary for achieving excellent performance have been elucidated. Let CO₂ pass! The influence of the variation of cross-link density in end-group cross-linked polydimethylsiloxane-norbornene (PDMSPNB) matrix on CO₂ permeability and CO₂/N₂ selectivity is investigated. Tuning cross-link densities of PDMS membranes using macromonomers can improve CO₂/N₂ separation significantly. The cross-linked PDMSPNB membranes give rise to excellent CO₂ permeability with good selectivity.