Aliphatic poly(amido acids) and polyimides with cyclobutane ring in the main chain

New aliphatic polyimides with cyclobutane ring in the main chain have been synthesized successfully from cyclobutane tetracarboxylic dianhydride and diamine. In order to establish the reaction path poly(amido acids), intermediates to polyimides, were isolated and characterized. All poly(amido acids) are hygroscopic and were found to be converted into polymides through dicarboacetoxy intermediate by heating in dimethylformamide at 100°C in the presence of acetic anhydride. Thermal study by means of thermal gravimetric analysis and differential scanning calorimetry revealed that conversion of poly(amido acid) to polyimide also occurred by thermal cyclocondensation reaction at around 180°C. These reactions were confirmed by parallel reaction of the model compounds. Properties of polyimides thus obtained were characterized and are discussed in comparison with known polymers with polyimide or cyclobutane ring structures.