Entropic selectivity analysis of a series of polypyrrolones for gas separation membranes

A series of 6FDA/PMDA-TAB polypyrrolone copolymers has been shown to exhibi t performance lying on or above the so-called O-2/N-2 upper bound membrane separation tradeoff limit. Further analysis of diffusion in these high perf ormance materials can potentially guide future structural enhancements, whi ch may lead to improved separation properties. This work compares and analy zes diffusion in this attractive family of hyperrigid polymers using entrop ic and energetic selectivities. When the polymer structure and penetrant si zes are examined, possible polymer matrix configurations can be discussed w ith regard to the entropy of the molecules in the normal and activated stat es. This analysis extends to O-2/CH4 and N-2/CH4 entropic selectivities, wh ich corroborate the trend observed with the O-2/N-2 gas pair, but the chang es are more pronounced due to the larger difference in penetrant size.