Aliphatic Polyimides Derived from Polyalicyclic Monomers

Abstract

Tetracarboxylic dianhydrides bearing a polyalicyclic structure, bicyclo[2.2.1]-heptane-2,3,5,6-tetracarboxylic 2,3:5,6-dianhydrides (BHDA), bicyclo[2.2.2]-octane-2,3,5,6-tetracarboxylic 2,3:5,6-dianhydrides (BODA), (4arH,8acH)decahydro-1t,4t:5c,8c-dimethanonaphthalene-2,3,6,7-tetracarboxylic 2,3:6,7-dianhydrides (DNDA), and bicyclo[2.2.1]heptane-2-exo,3-exo,5-exo-tricarboxyl-5-endo-acetic 2,3:5,5-dianhydride (BSDA) were synthesized and polycondensated with aromatic diamines or a polyalicyclic diamine, bis(aminomethyl)bicyclo[2.2.1]heptane (BBH), in DMAc, NMP, DMI or HMPA at room temperature or 60–105°C under nitrogen. The polymerization solutions gave the flexible and free-standing polyimide films after being cast on glass plates and then cured. The films were soluble in aprotic polar solvents such as DMAc and NMP at room temperature. Among the films, some dissolved in CHCl3 or 1,4-dioxane. The polyimides showed good thermal stability and the 5% weight loss temperatures in N2 were over 450°C. The polyimide films exhibited Tg values in the range of 280–400°C. The cutoff wavelengths of the non-aromatic polyimides such as PI(DNDAdx-BBH) and PI(BHDAdx-BBH) were shorter than 235 nm, and around 290–330 nm for the semi-aromatic polyimides. The transparencies in the visible region (400–780 nm) were over 85%. The flexible polyimide films possessed an average refractive index range of 1.522–1.617, and the optical anisotropies were 0.000–0.017. The dielectric constant ε values that were estimated from the refractive indices according to the modified Maxwell’s equation were 2.55–2.87.