The effect of benzimidazole units on thermal imidizaiton was studied when they were introduced into the main chain of poly(amic acid) (PAA). The thermal imidization process of PAA-PABZ synthesized by 3

3'

4

4'-biphenyltetracarboxylic dianhydride (BPDA) and 2-(4-aminophenyl)-5(6)-aminobenzimidazole (PABZ) was studied by TGA

DSC

DMA

FTIR and

in situ

FTIR. The results of FTIR and

in situ

FTIR indicate benzimidazole units act as an "

in situ

" catalyst to accelerate thermal imidization of PAA to polyimide (PI) when the temperature is lower than 170℃. FTIR and 1H-NMR results demonstrate that

in situ

catalysis is caused by the hydrogen bonding interactions between C=N of benzimidazole and ―NH― in ―CONH― of PAA and the semi-ionization of the H in imidazole ring of benzimidazole. However

when the imidization temperature is higher than 170℃

the thermal imidization process is inhibited. DMA and

in situ

FTIR results illustrate that the decreased mobility of PI-PABZ macromolecular chains and the reduced reactive ability of anhydride formed during the intramolecular breakdown of polymer chains lead to the inhibition of thermal imidization process.