Thermal properties and solubility of poly‐1,4,5,8‐naphthalenetetracarboxydiimides containing 1,3,5‐triazine rings

Aromatic polyimides were synthesized by polymerization of 1,4,5,8‐naphthalenetetracarboxylic dianhydride and 2‐dialkylamino‐4,6‐dihydrazino‐1,3,5‐triazines by a solution polymerization method followed by cyclodehydration. The polyimides had number‐average molecular weights over 13,000–16,000 or viscosity values of 0.23–0.65 dl/g. The x‐ray diffraction diagram of polyimide I showed a crystal pattern, but the pattern became less pronounced with increasing length of the polymer side chain, and thus polyimide V showed a typical amorphous pattern. Study of the thermal stability of the polyimides by thermogravimetric analysis showed that a steep weight loss occurred in the range 380–410°C. Among the polyimides, I had only poor solubility in organic solvent, while IV and V were soluble even in general organic solvents such as tetrahydrofuran and dioxane.