In-depth understanding of the role of methanesulfonic acid in nitrile group conversion of PIM-1

Abstract

Polymers of intrinsic microporosity (PIMs) exhibit unique structural properties, characterized by high surface area and rigid, twisted molecular configurations that hinder polymer chain stacking, resulting in micropores favorable for gas transport. PIM-1, a prominent member of this class, has been extensively explored for gas separation applications. However, its industrial use is limited by physical aging and low selectivity. To address these limitations, nitrile group functionalization in PIM-1, such as carboxyl group formation, has been investigated. In this study, we explore the hydrolysis of nitrile groups in PIM-1 under acidic conditions using pure methanesulfonic acid (MSA) and MSA/water mixtures. By systematically varying reaction parameters, we elucidate the transformation mechanism of nitriles to carboxylic acids. Results indicate that nitriles are effectively converted into the corresponding amides in pure MSA, while carboxylic acids (up to 80 %) in MSA/H₂O mixtures. Characterization techniques, including FTIR, ¹H NMR, UV–Vis spectroscopy, wide-angle X-ray diffraction (WAXD) and wide-angle X-ray scattering (WAXS), confirm the structural changes in the polymer and reveal contraction in interchain spacing due to hydrogen bonding. This study provides insights into optimizing the hydrolysis conditions for enhanced performance of PIM-based membranes in gas separation applications.