Structure-property relationship study of partially aliphatic copolyimides for preparation of flexible and transparent polyimide films

The structure-property relationship of partially aliphatic copolyimides has been studied for the development of flexible, transparent polyimide films. A structurally rigid cycloaliphatic dianhydride and three aromatic dianhydrides having different structural flexibility were reacted with 4,4′-oxydianiline to prepare the copolyimides. In order to control the balance between aromaticity and aliphaticity and between rigidity and flexibility of the copolyimides, the molar ratio of the dianhydrides was varied. Polyimide properties such as viscosity, solubility, optical transparency, color, dielectric constants, film flexibility and thermal stability are influenced by aromaticity/aliphaticity and/or flexibility/rigidity of the monomers.