writer：XiaofanHu Won Hee Lee Jiayi Zhaob Ju Sung Kim ZhenWang Jingling Yan Yongbing Zhuang Young Moo Leea
keywords：Thermally rearranged polymer membranes
source：期刊
specific source：Journal of Membrane Science
Issue time：2020年

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.