PEG/PPG–PDMS-Based Cross-Linked Copolymer Membranes Prepared by ROMP and In Situ Membrane Casting for CO₂ Separation: An Approach to Endow Rubbery Materials with Properties of Rigid Polymers

Abstract

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.

PEG/PPG-PDMS-Adamantane-Based Crosslinked Terpolymer Using the ROMP Technique to Prepare a Highly Permeable and CO2-Selective Polymer Membrane

“…Furthermore, in the x(10:0.5:0.5) membrane, despite decreasing PDMS content, the degree of permeability was found to increase, and a loss of permeability was observed in the x(10:0:1) membrane. This trend differs from that in our previous reports of permeability and selectivity for crosslinked membranes made of only PEG/PPG and PDMS [ 23 ], where the permeability increased while the selectivity decreased with an increase in PDMS content.…”

“…Nevertheless, the diffusivity of the crosslinked x(10:0:1) membrane for N 2 and CH 4 was higher than that of our previously developed x(PEG/PPG:PDMS)(1:0.10) membrane, which was made of only PEG/PPG and PDMS [ 23 ]. Therefore, as was the goal of this study, it is confirmed that diffusivity can be increased by introducing the bulky and rigid adamantane unit, while also controlling the degree of crosslinking.…”

“…More specifically, the higher the PDMS content, the larger and more connected the sphere-shaped phases formed ( Figure 8 d). It should be noted that, in our previous study based on crosslinked membranes formed from PEG/PPG and PDMS, the size of this sphere-shaped phase gradually increased as the content of PDMS decreased [ 23 ]. However, the size tended to decrease when PDMS decreased in the current x(PEG/PPG:PDMS:Ad) membranes.…”

“…To examine the gas separation properties of the crosslinked terpolymer x(PEG/PPG:PDMS:Ad) membranes with respect to the content of PDMS and adamantane, the single gas permeability of each polymer membrane to CO 2 , N 2 , and CH 4 was measured at 2 atm and 30 • C, the results of which are presented along with the selectivity data in Table 3. In addition, the results were compared with those for our previously developed crosslinked membrane composed of only PEG/PPG and PDMS (Table S1) [23]. Firstly, a very high permeability to CO 2 gas was obtained for these crosslinked terpolymer membranes.…”

“…From this perspective, we recently developed a crosslinked copolymer of PEG/PPG and PDMS using the ring opening metathesis polymerization (ROMP) method, and then studied the gas separation properties of the corresponding membranes [ 23 ]. We found that the crosslinked membranes not only had a high affinity to CO 2 owing to PEG, and the PDMS had high permeability, but also exhibited a size-sieving capability not commonly found in rubbery polymers.…”