SYNTHESIS,CHARACTERIZATION,AND GAS PERMEATION PROPERTIES OF COPOLYIMIDES

Abstract

The goal of this work is to explore new polyimide materials that exhibit both a high permeability and a high selectivity for specific gases. copolyimides offer the possibility of preparing membranes with gas permeabilities and selectivities not obtainable with homopolyimides. a series novel fluorinated copolyimides were synthesized with various diamine compositions by chemical imidization in a two-pot procedure. polyamic acids were prepared by stoichiometric addition of solid dianhydride in portion wise to the diamine ( s) the gas permeation behavior of 2,2'-bis ( 3, 4'-dicarboxyphenyl) hexafluoropropane dianhydride ( 6fda)-2, 6-diamine toluene ( dat)/1, 3-phenylenediamine ( mpda) polyimides were investigated. the physical properties of the copolyimides were characterized by ir, dsc, and tga. glass transition temperature increased with increase in dat content. all the copolyimides were soluble in most of the common solvents. the gas permeabilities coefficients decreased with increasing mpda content; however, the permselectivity of gas pairs such as h-2/n-2, o-2/n-2, and co2/ch4 was enhanced with the incorporation of mpda moiety. the permeability coefficients of h-2, o-2, n-2, co2 and ch4 were found to decrease with the increasing order of kinetic diameters of the penetrant gases. 6fda-2,6-dat/mpda (3 : 1) copolyimide and 6fda-2,6-dat polymide had high separation properties for h-2/n-2, o-2/n-2 co2/ch4. the h-2, o-2 and co2 permealtilities were 64.99 barrer, 5.22 barrer, 23. 87 barrer and 81.96 barrer, 8.83 barrer, 39.59 barrer respectively at 35 degrees c and 0.2 mpa ( 1 barrer = 7.5 x 10(-14) cm(3) (stp)center dot cm center dot cm-2 center dot s(-1)center dot pa-1); and the ideal selectivities of h-2/n-2, o-2/n-2 and co2/ch4 were 69.61, 6.09, 63.92 and 53.45, 5.76, 57.41, respectively. moreover, all of the copolyimides studied in this work exhibited performance near, lying on or above the existing upper bound trade-off line between permselectivity and permeability. it may be utilized as commercial gas separation membrane material.