Soluble and colorless polyimides with polyalicyclic structures [1]

Abstract Two tetracarboxylic dianhydrides with polyalicyclic structure, bicyclo[2.2.2]octane-2- endo , 3- endo , 5- exo , 6- exo -2,3:5,6-dianhydride ( 5a ) and the all- exo isomer ( 5b ), were synthesized in six steps using phthalic acid as a starting material. The dianhydrides were polymerized at 85–105°C in well-purified DMAc with aromatic diamines which were purified by two recrystallizations and then sublimation. The polyimides formed flexible and tough films, and were soluble in aprotic polar solvents such as DMAc. The 5%-weight loss temperatures were over 450°C. The polyimides possessed glass-transition temperatures in the range from 211 to 385°C. The polyimides films had a tensile modulus range of 1.5–2.6 GPa, a tensile strength range of 52–96 MPa, and an elongation range at break of 3–11%. The polyimide films showed cutoffs at wavelengths shorter than 320 nm and were entirely colorless. The colorlessness of the polyimide films was maintained up to 200°C when heated in air and to 400°C in a N 2 atmosphere.