Highly Selective Membranes Based on Polydecylmethylsiloxane for VOC Removal: The Influence of α,ω-Diene Cross-Linker Length and Concentration

Membrane separation is an efficient approach for volatile organic compound (VOC) recovery from industrial off-gases due to its low energy consumption, compact design, and operational simplicity. Membrane-based VOC recovery critically depends on the membrane material, which must exhibit high VOC permeability and selectivity under mixed-gas conditions. In this study, novel highly selective membranes for VOC removal based on polydecylmethylsiloxane (PAMS-10) were synthesized using both polydimethylsiloxane and various α,ω-dienes as cross-linkers: 1,7-octadiene (OD), 1,9-decadiene (DD), and 1,11-dodecadiene (DdD). The influence of cross-linker concentration and length on mechanical, structural, sorption, and transport properties was examined extensively. The combination of three independent experimental methods (time-lag, vapor permeation, and in situ spectroscopic ellipsometry) revealed that increasing α,ω-diene concentration and decreasing its length led to a reduction in the diffusivity and permeability of permanent gases, gaseous hydrocarbons, and VOC vapors. For VOC/N2 separation, the slightly cross-linked OD-1 membrane and the DdD-5 membrane, cross-linked with long 1,11-dodecadiene, demonstrated outstanding mixed-gas selectivities of 950/921/314/840 and 940/1084/233/1106 for toluene/n-octane/i-octane/n-butyl acetate, respectively. Notably, the DD-5 membrane, cross-linked with 1,9-decadiene, matching the length of the PAMS-10 side chain substituent, exhibited the best mechanical properties and mixed-gas selectivity comparable to the ideal selectivity, a unique behavior attributed to optimal supramolecular organization.