Thermally rearranged polybenzoxazoles made from poly(orthohydroxyamide)s. Characterization and evaluation as gas separation membranes

Two series of aromatic poly(ortho-hydroxyamide)s (poly(o-hydroxyamide)s, HPAs) were prepared by reaction of two diamines, 2,2-bis(3-amino-4-hydroxyphenyl) propane (APA) and 2,2-bis(3-amino-4-hydroxyphenyl) hexafluoropropane (APAF), with four aromatic diacid chlorides; terephthaloyl dichloride (TPC), isophthaloyl dichloride (IPC), 2,2-bis[4-chlorocarbonylphenyl)hexafluoropropane (6FC) and 4,4¿-sulfonyldibenzoyl dichloride (DBSC). Amorphous HPAs with high molecular weights (inherent viscosities higher than 0.5 dL/g) and relatively high glass transition temperatures (220¿280 °C) were obtained. Dense membranes of HPAs were able to undergo a thermal rearrangement (TR) process to polybenzoxazoles (ß-TR-PBOs) heating at moderate temperatures (between 250 and 375 °C), and their complete conversion was reached at a temperature below 375 °C, depending on the o-hydroxy diamine moiety, APA and APAF. The ß-TR-PBOs films derived from APAF showed a higher thermal stability and higher Tg than those from APA. Gas separation properties of TR-PBOs membranes were superior to those of their poly(o-hydroxyamide) precursors, particularly for the following gas pairs: O2/N2, CO2/CH4, He/CH4 and He/CO2.The financial support provided, by the Spain's MINECO (MAT2013- 45071-R and MAT2016-76413-C2-1-R and MAT2016-76413-C2-2-R AEI/FEDER, UE and CTQ 2012-31076) is greatly acknowledged. This research was also supported by the Korea Carbon Capture & Sequestration R&D Center (KCRC) through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT, and Future Planning (NRF-2014M1A8A1049305). We are also indebted to the Spanish Junta de Castilla y León for its funding help (project VA248U13). Authors kindly acknowledge Sara Rodriguez for carrying out the gas separation tests and Judit González Jarillo for performing polymer characterizationPeer Reviewe