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 H2/N2

O2/N2

and CO2/CH4 was enhanced with the incorporation of mPDA moiety.The permeability coefficients of H2

O2

N2

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 polyimide had high separation properties for H2/N2

O2/N2

CO2/CH4.The H2

O2 and CO2 permeabilities were 64.99 Barrer

5.22 Barrer

23.87 Barrer and 81.96 Barrer

8.83 Barrer

39.59 Barrer respectively at 35℃ and 0.2 MPa (1 Barrer=7.5×10-14 cm3 (STP.cm.cm-2.s-1.Pa-1); and the ideal selectivities of H2/N2

O2/N2 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.