In this paper, we report the materials design,synthesis and characterization of a class of new multicomponent polymeric membranes where some larger molecules can permeate faster than smaller ones, or so-called reverse-selective gas separation membranes. Reverse-selective gas separation membranes have attracted much attention owing to their advantages for certain commercial gas separation applications, for example CO2 removal from H2. These newly designed and synthesized copolymers consist of alternating PEO sequences and rigid iptycene-containing polyimide segments, wherein the bulky iptycene-containing imide sequences provide high gas permeability and mechanical strength via the unique chain “threading” and “interlocking” mechanism, while the CO2-philic characteristic of PEO sequences provides high solubility selectivity towards CO2. The copolymers are systematically varied in their chemical structure in terms of PEO sequence length (from 600 to 2,000 g/mol), PEO weight fraction (20% - 60% wt), and iptycene structure (triptycene vs. pentiptycene). FTIR and 1H NMR confirmed the desired macromolecular structure of the copolymers as well as the target PEO content. Physical properties such as glass transition temperature, mechanical properties, and thermal stability were shown to strongly depend on the chemical structure/composition of the multicomponent copolymers. Similarly gas transport properties were very sensitive to the detailed phase morphologies in these membranes. Relating the permselectivity with the copolymer composition suggested that there might be a competing effect between the reduced size-sieving diffusion due to minimization of free volume by chain “threading” and the preferential sorption of larger condensable CO2 by increasing PEO content, which led to a “turnover” trend producing reverse-selective membranes.

Reverse-selective gas separation membranes based on segmented copolymers of PEO and iptycene-containing polyimides

249th National Meeting (2015)

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