Thermal Durability Improvement in Transparency of Alicyclic Polyimide by Capping Terminal Amino Groups

The alicyclic dianhydride (CpODA) was polycondensated with an aromatic diamine (4,4'-DDE) at room temperature. The poly(amic acid)s gave flexible and tough films by a thermal imidization method in the presence or the absence of acetic anhydride (Ac2O). The resulting polyimide films were absolutely colorless. These polyimide films were reheated in the air at 300 oC and 350 oC for each 0.5 h. The thermal durability in transparency was extremely improved by adding Ac2O and the effect was increased as an increase in the amount of Ac2O. It was tried to prepare colorless alicyclic polyimide films in the air by thermal imidization. Several kinds of acylation reagents were used for end-capping. All the polyimide films prepared by thermal imidization in the air at 350 oC took brown color. However, it is found that two carboxylic anhydrides, Ac2O and TFAA, showed a transparency improvement effect of alicyclic polyimide films even on the thermal imidization in the air.