Rubbery
polymer membranes prepared from CO2-philic PEO
and/or highly permeable PDMS are desired for efficient CO2 separation from light gases (CH4 and N2).
Poor mechanical properties and size-sieving ability, however, limit
their application in gas separation applications. Cross-linked rubbery
polymer-based gas separation membranes with a low T
g based on both PEG/PPG and PDMS units with various compositions
between these two units are prepared for the first time in this work
by ring-opening metathesis polymerization type cross-linking and in
situ membrane casting. The developed membranes display excellent CO2 separation performance with CO2 permeability ranging
from 301 to 561 Barrer with excellent CO2/N2 selectivity ranging from 50 to 59, overcoming the Robeson upper
bound (2008). The key finding underlying the excellent performance
of the newly developed cross-linked x(PEG/PPG:PDMS)
membranes is the formation of a well-connected interlocked network
structure, which endows the rubbery materials with the properties
of rigid polymers, e.g., size-sieving ability and high thermomechanical
stability. Moreover, the membrane shows long-term antiaging performance
of up to eight months and antiplasticization behavior up to 25 atm
pressure.
Mixed-matrix membranes (MMMs) with an ideal polymer−filler interface and high gas separation performance are very challenging to fabricate because of incompatibility between the fillers and the polymer matrix. This work provides a simple technique to prepare a series of cross-linked MMMs (xMMM@n) by covalently attaching UiO-66-NB metal−organic frameworks (MOFs) within the PEG/PPG−PDMS copolymer matrix via ringopening metathesis polymerization and in situ membrane casting. The norbornene-modified MOF (UiO-66-NB) is successfully copolymerized and dispersed homogeneously into a PEG/PPG− PDMS matrix because of very fast polymer formation and strong covalent interaction between MOFs and the rubbery polymer. A significant improvement in gas permeability is achieved in membranes up to a 5 wt % MOF loading compared to the pristine polymer membrane without affecting selectivity. The CO 2 /N 2 separation performance of xMMM@1, xMMM@3, and xMMM@5 with 1, 3, and 5 wt % MOF loading, respectively, surpassed Robeson's 2008 upper bound. In addition, the best performing membrane, xMMM@3 (P CO 2 = 585 Barrer and CO 2 /N 2 ∼53), approaches the 2019 upper bound, indicating that the cross-linked MMMs (xMMM@n) are very promising for CO 2 separation from flue gas. The experimental results of our study were evaluated and are supported by theoretical data obtained using the Maxwell model for MMMs. Moreover, the developed MMMs, xMMM@ns, displayed outstanding antiplasticization performance at pressures of up to 25 atm and very stable antiaging performance for up to 11 months with good temperature switching behaviors.
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