Thermally rearranged polymer membranes containing highly rigid biphenyl ortho-hydroxyl diamine for hydrogen separation

• DOI: 10.1016/j.memsci.2020.118053
• Publication Date: 2020-03-20T07:06:12Z
• Authors: Xiaofan Hu; Won Hee Lee; Jiayi Zhao; Ju Sung Kim; Zhen Wang; Jingling Yan; Yongbing Zhuang; Young Moo Lee
• Keywords: Pyromellitic dianhydride; Polyetherimide; Biphenyl

Abstract A novel bulky and rigid ortho-hydroxyl diamine, 3,3′-diamino-5,5′,6,6′-tetramethyl-[1,1′-biphenyl]-2,2′-diol (TMBDA), was synthesized for gas separation membranes in this study. The chemical structure of TMBDA with four methyl groups and a fixed twist biphenyl center was rationally designed, and consequently presented a superior energy barrier of rotation, which efficiently suppressed chain motion and enhanced polymer rigidity. Four types of TMBDA-based polyimides (PIs) were prepared with two commercially available dianhydrides, i.e., 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and pyromellitic dianhydride (PMDA), from two different synthetic routes, azeotropic and chemical imidization. Thermally rearranged (TR) polymers were obtained from TMBDA-based PIs by thermal treatment at various temperatures. Thermal properties and physicochemical characteristics of TMBDA-based PIs and TR polymers were investigated. The resulting polymers exhibited high glass transition temperatures (Tg) and contorted backbone structures with three discrete d-spacing values, where the smallest interchain d-spacing was located between the kinetic diameters of H2 and CH4 molecules. Moreover, TMBDA-based TR polymers showed outstanding performances in hydrogen separation with comparable H2 permeability and higher selectivity than reported TRs. For instance, 6F-TM-Ac-425 exhibited a H2 permeability of 325 Barrer with H2/CH4 and H2/N2 selectivities of 50 and 39, respectively, approaching to the 2008 Robeson upper bound.