Alicyclic polyimides – a colorless and thermally stable polymer for opto-electronic devices

Alicyclic polyimides were prepared from polyalicyclic monomers using a two-step method. Light absorption of polyimides was elucidated from quantum chemistry. The alicyclic polyimide films were colorless, and the transparencies in the visible region were over 85%. The semi-aromatic polyimide films had an average refractive index range of 1.599 to 1.617, and that of a full-alicyclic polyimide was 1.522. The birefringencies were nearly zero. Semi-aromatic polyimides were soluble in aprotic polar solvents like DMAc. However, the non-aromatic (full-alicyclic) polyimides were insoluble except sulfuric acid. All the alicyclic polyimides have the 5% weight loss temperatures in nitrogen over 450 °C, and 400 °C in air. They possess glass transition temperatures over 280 °C. The alicyclic polyimide films have a tensile modulus range of 1.3–3.0 GPa, and a tensile strength range of 38–145 MPa. Especially semi-aromatic polyimide films display high strength. They have an elongation at break range 5–30%. All the polyimides exhibited amorphous patterns and broad dispersive peaks of diffraction around at 16° (2θ).