Oxygen-and nitrogen-containing motifs are reminiscent of imines and polyethers, which are known to be high performing polymer membranes. Interestingly, our initial analysis using the Polymer Genome software suggests that most of the top 100 fittest polymers have high glass transition temperature-well above the standard operating conditions (> 400 K). We note that the three polymers in the experimental data set that are above the CO 2 /N 2 upper bound also have glass transition temperatures around 400 K. We speculate that the superior performance of these glassy amorphous polymers for gas separation may be due to their high fractional free volume and high number of microvoids . It remains an open question whether or not these polymers are easily synthesizable and easy to implement as membranes given their complicated chemistry. Further computational and experimental studies will be required to better understand these polymers and their efficacy as membrane materials.