Facile and Time-Efficient Carboxylic Acid Functionalization of PIM-1: Effect on Molecular Packing and Gas Separation Performance
Katherine Mizrahi Rodriguez, Albert X. Wu, Qihui Qian, Gang Han, Sharon Lin, Francesco M. Benedetti, Hyunhee Lee, Won Seok Chi, Cara M. Doherty, Zachary P. Smith
Abstract
An optimized acid hydrolysis method was developed to yield carboxylic acid-functionalized PIM-1 (PIM-COOH) with >89% conversion in 48 h using a postpolymerization reaction of PIM-1. Physical characterization of PIM-1 and PIM-COOH revealed that the average size of free volume elements in PIM-COOH decreased relative to that in PIM-1. Compared to PIM-1, PIM-COOH showed a significant increase in CO2- and H2-based selectivities with a corresponding decrease in permeabilities and sorption capacities for all gases considered. The dual-mode sorption model, time-lag method, and sorption–diffusion model were applied to glean molecular-level insights into diffusion and sorption in these polymers. Results indicate that improvements in selectivities for CO2-based gas pairs for PIM-COOH are primarily driven by diffusion selectivity and that PIM-COOH displays transport behavior consistent with the sorption–diffusion model. To better understand performance under more realistic conditions, pure- and mixed-gas permeation values for CO2/CH4 are reported for a 330 day aged PIM-COOH sample.