In the process for producing polyimides by heating an aromatic tetracarboxylic dianhydride and an aliphatic diamine in the presence of a catalyst in a solvent to effect addition condensation, the first reaction process which accompanies a temperature rise by initial exothermic heat is carried out by using crotonic acid as the catalyst, and subsequently the second reaction process to heat at a temperature of not lower than the temperature reached by the initial exothermic heat is carried out. 触媒の存在下、溶媒中で芳香族テトラカルボン酸二無水物と脂肪族ジアミンとを加熱し付加縮合するポリイミドの製造方法において、触媒としてクロトン酸を用い、初期発熱による温度上昇を伴う第1反応プロセスを行い、ついで該初期発熱による到達温度以上の温度で加熱する第2反応プロセスを行うことを特徴とする半芳香族ポリイミドの製造方法。 - 特許庁