Polyethylene oxide rubbery organic framework (ROF) membranes with enhanced CO2 permeability and CO2/CH4 selectivity

Abstract

Rubbery organic frameworks (ROFs), assembled via reversible covalent bonds under dynamic molecular control, represent a promising class of adaptive polymers for gas separation membranes. Elastomeric ROF membranes exhibit excellent mechanical stability, dynamic responsiveness, and intrinsic microporosity. Their affinity for carbon dioxide (CO 2 ) enables both high CO 2 permeability and enhanced selectivity compared to conventional glassy polymeric membranes. One effective strategy for improving CO 2 separation performance is the incorporation of polyethylene oxide (PEO) units into the ROF structure. Owing to the high CO 2 solubility and electrostatic interactions with PEO segments, this approach can significantly boost CO 2 selectivity over other gases such as methane (CH 4 ). In this study, a new class of PEO-based ROF membranes were developed and tailored by varying the length of PEO segments to optimize both mechanical strength and CO 2 /CH 4 separation performance. The membranes were systematically characterized to understand the relationship between their molecular architecture, morphology, and gas transport properties. The resulting ROF membranes demonstrated CO 2 permeabilities ranging from 155 to 180 barrer and CO 2 /CH 4 selectivities between 15 and 31. Notably, a synergistic enhancement in both CO 2 permeability and selectivity was observed with increasing PEO segment length. This improvement is attributed to a favorable balance of polymer chain packing, diffusivity, and CO 2 affinity within the membrane matrix. These findings highlight the potential of PEO-integrated ROFs as versatile and high-performance materials for advanced gas separation applications.