Xi Ren,Duanyi Li,Zhibin He,Ruixuan Wang,Changxu Yang,Shujun Han,Haifeng Yu,Jingang Liu
Fluorine-free, fully aromatic polyimide (PI) films, characterized by the excellent optical transparency and high-temperature endurance, have been successfully synthesized through either homopolymerization or copolymerization of an ester-containing diamine, 2-(4-aminobenzoate)-5-aminobiphenyl (ABABP) and two distinct dianhydrides: 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA) and 9,9-bis[4-(3,4-dicarboxyphenoxy)phenyl]fluorene dianhydride (BPFPA). Owing to the good solubility of the developed PI-I to PI-V resins in polar aprotic solvents, particularly in N,N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP) and N,N-dimethylformamide (DMF), the synthesis process was performed through a two-stage chemical imidization technique. The polymer solutions of PI-I to PI-V in DMAc were fabricated into films that showed exceptional optical clarity, featured with the ultraviolet cutoff wavelength (λ) below 375 nm, the light transmission at 450 nm (T 450 ) surpassed 80%, the b * values (CIE indices) below 4.5, and the turbidity percentage (haze values) under 0.5%. Despite the fact that a higher molar concentration of BPFPA components in the dianhydride segments led to a decline in the optical characteristics of the films, the thermal resistance was concurrently enhanced. The resulting copolymerized PI films exhibited a glass transition temperature (T g ) over 264.9°C, along with the coefficients of linear thermal expansion (CTE) values of 56.7 ~ 65.9 ppm/K in temperature range of 50 ~ 200°C.
Tongxin Liu,Ruili Zhang,Guang-Rui Si,Bin Liu,Yabo Xie,Lin-Hua Xie,Jian-Rong Li
The rational design of mixed matrix membranes (MMMs) combining appropriate additives and industrial processable polymers offers a new prospect for highly efficient membrane separations. However, the difficulty in their fabrication due to the lack of processability of most additives and the formation of segregated filler domains in polymer matrices hampers the development and application of MMMs. Herein, we present two new zirconocene-based metallocavitands (ZRA and ZRT) and a series of MMMs fabricated by blending ZRA, ZRT, and MOC-1-NH2 (a zirconocene-based metal–organic cage) with the polyimide (6FDA-DAM), respectively. It was found that ZRA exhibited high thermal stability and good solubility in various solvents, which can be homogeneously mixed with polymers to prepare ZRA-based MMMs without any indication of filler agglomeration. Compared to the pure 6FDA-DAM membrane, a low ZRA-loading MMM (ZRA-2.2%) exhibited better mechanical properties and 50% improved CO2 permeability for CO2/CH4 separation. ZRA-2.2% also exhibited a good performance after 6 months of aging and significantly alleviated the plasticization effect under high pressures. These results suggest the great potential of the ZRA-2.2% for CO2/CH4 separation and that the simple metallocavitands may serve as promising additives in fabricating MMMs for gas separations.
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