Novel polyethylene glycol methyl ether substituted polysiloxane membrane materials with high CO2 permeability and selectivity

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Membrane gas separation is a promising technology for CO2 capture. However, one of the key challenges is the development of stable-in-time and highly permeable materials with increased CO2 permselectivity. In this study, two series of novel polysiloxanes with linear (methyl oligoethyleneglycol allyl ether (PEG8)) and branched (vinyl-bis- [methyltriethyleneglycol] (B-PEG4)) oxygen-containing side substituents were synthesized. By crosslinking PEG-substituted polymethylsiloxanes with polydimethylsiloxane (PDMS), a series of CO2-highly selective membrane materials with a PDMS content of 6.5–50 wt% was obtained for the first time. The effect of the side chain geometry on the sorption and transport properties of these membranes for different gases (N2, O2, CO2, CH4, C2H6) was evaluated. The specific interactions between the PEG substituents and CO2 that contribute to the enhanced selectivity of these materials were identified. The introduction of both linear and branched PEG substituents leads to in an increase in the selectivity of diffusion, solubility, and CO2/gas permeability, compared to PDMS.The CO2/N2 and CO2/CH4 permselectivities and diffusion selectivities are increases, as well as the permeability coefficients of the membrane materials for all gases are decreases, as the PDMS content reduces from 50 % to 6.5 % wt. Within the PDMS concentrations range between 6.5 and 12.5 % wt., there was a sharp increase in diffusion and permeability coefficients of membrane materials. For this polysiloxanes with linear PEG substituents, an unexpectedly high diffusion selectivity for CO2 was observed. Such value determined the maximum CO2 permselectivity among the polysiloxanes studied. The most promising membrane material from these series was identified as PEG8-substituted polysiloxane with 12.5 wt% PDMS. It has a CO2 permeability coefficient of 1300 Barrer, CO2/N2 selectivity of 37 and CO2/CH4 selectivity of 10.