A novel diamine monomer

2

5-bis(N

N-dimethylamino)methyl)-1

4-bis(4-aminophenoxyl)benzene (DMAPB)

was synthesized.A series of sulfonated polyimide (SPI) were prepared from DMAPB

1

4

5

8-naphthalenetetracarboxylic dianhydride (NTDA) and sulfonated diamine (ODADS).By varying the molar ratio of the sulfonated diamine to the unsulfonated diamine

copolymers with 40%~ 80% sulfonation degree were obtained.The SPI membranes were obtained via solution casting with m-cresol as the solvent.The nitrogen atoms introduced in the side chains of the SPI could effectively resist membrane swelling due to the strong interchain interactions through basic nitrogen atoms and sulfonic acid groups.The copolymer SPI-40 showed higher water stability

it could maintain mechanical strength after being soaked in 100℃ liquid water for more than 1000 h.The copolymers were thermally stable up to 330℃ and displayed good oxidative stability.The membranes exhibit methanol permeability from 2.05 10-7 to 5.11 10-7cm2/s at 20℃

which was much lower than that of Nafion (2 10-6cm2/s).The SPI also showed reasonable mechanical strength under high moisture conditions.However

the cross-linked membranes showed lowered proton conductivities than the uncross-linked ones because that the crosslinking resulted in the more compact structure of membranes

which decreased the water uptake and hindered the mobility of water and H+.In addition

a part of the sulfonic acid groups was consumed during the cross-linking process.