Preparation and Performance of Thermally Rearranged Gas Separation Membranes Containing Tetraarylimidazole Structure
In recent years,the thermal rearrangement(TR)membrane materials derived from hydroxyl-containing polyimides(HPI)as precursors have received extensive attention in the field of gas separation.In this study,the dihydroxy compound 4,4'-(4,5-diphenyl-(4-hydroxyphenyl))imidazole(PMOPPP)containing rigid and bulky tetraarylmidazole structure was first synthesized,and then reacted with 5-fluoro-2-nitrophenol to produce a dinitro compound 4,4'-(4,5-diphenyl-(3-hydroxy-4-nitrophenoxy)phenyl)imidazole(PMNPPP).After reduction treatment,a new kind of diamine monomer 4,4'-(4,5-diphenyl-(3-hydroxy-4-aminophenoxy)phenyl)imidazole(PMAPPP)was obtained.Then,the diamine PMAPPP was separately polymerized with five kinds of dianhydride monomers,followed by thermal imidization treatment to obtain HPI membranes.Subsequently,these membranes were further thermally treated at 450 ℃ for 1 h to obtain the corresponding TR membranes,and the structure and performance of these membrane materials were characterized.The testing results showed that the introduction of rigid and large volume tetraarylimidazole structure resulted in excellent thermal and mechanical properties of five HPI membranes,and the glass transition temperatures(Tg)were in the range of 263-361 ℃ and the tensile strength ranged from 98.4 MPa to 118.3 MPa.Compared to HPI membrane materials,the gas separation performances of TR membranes were significantly improved.Among them,the TR(PMAPPP-6FDA)exhibited the highest gas permeabilities,namely H2(269.31 Barrer),CO2(284.25 Barrer),O2(62.75 Barrer)and N2(10.67 Barrer).Moreover,the ideal selectivities of CO2/N2,O2/N2 and H2/N2 were 25.24,5.88 and 26.64,respectively,and the O2/N2 separation performance was beyond the 2008 Robeson upper bound.
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