Design of gas separation membranes derived of rigid aromatic polyimides. 1. Polymers from diamines containing di-tert-butyl side groups

摘要: Abstract A series of polyimides has been obtained from the experimental diamine 1,4-bis(4-aminophenoxy)2,5-di-tert-butylbenzene (TBAPB) and three commercial dianhydrides, i.e. pyromellitic dianhydride (PMDA), 3,3′,4,4′-byphenyltetracarboxylic dyanhidride (BPDA) 4,4′-hexafluoroisopropyliden diphthalic anhydride (6FDA), following classical polyimidation methods. Analogous with diamines 2,2-bis(4-aminophenyl)hexafluoropropane (6FpDA) 1,4-bis(4-aminophenoxy)benzene (APB) have also prepared for comparative purposes. All showed high thermal stability, decomposition temperatures above 490 °C, glass transition higher than 270 °C. The rigid, rod-like structure PMDA, combined bulky TBAPB 6FpDA, yielded fractional free volume (FFV), close to that 6FDA–6FpDA. FFV PMDA–TBAPB contrasts its fairly large degree short range order as evidenced by X-ray diffraction. gas permeation properties were greatly dependent on moiety and, a rule, they compared well those used separation. polymers PMDA–6FpDA, best productivity values. By means molecular modelling calculations, it observed monomer preferably adopts contorted, rotation-restricted conformation, what can explain special characteristics in reported polyimides.