Influence of curing accelerators on the imidization of polyamic acids and properties of polyimide films

In order to lower the imidization temperature of polyamic acids (PAA), the catalytic activities of the curing agents p-hydroxybenzoic acid (PHA), quinoline (QL), benzimidazole (BI), benzotriazole (BTA), triethylamine (Et3N) and 1, 8-diazabicyclo [5.4.0]undec-7-ene (DBU) were investigated in the process of thermal imidization of PAA. In addition, the effect of these various curing agents on the thermal stabilities and mechanical properties of the resultant polyimide (PI) films was determined. Quinoline was found to be an effective curing accelerator in the use of two-step method for synthesizing PI. Due to its moderate base strength, low steric crowding effect and moderate boiling point, quinoline could not only accelerate PAA to achieve imidization completely at 180 °C, but also maintain the mechanical properties and thermal stability of the ordinary PI film. Any residual quinoline could be removed from PI films by heating at 250 °C for 4 h.