Highly transparent and organosoluble polyimides derived from 2,2′-disubstituted-4,4′-oxydianilines

To improve the optical transparency and organosolubility of aromatic polyimides derived from 4,4′-oxydianiline (4,4′-ODA), two new aromatic diamines, 2,2′-diiodo-4,4′-oxydianiline (DI-ODA) and 2,2′-bis[(p-trifluoromethyl)phenyl]-4,4′-oxydianiline (BTFP-ODA) were synthesized by using 4,4′-ODA as a starting material. Novel polyimides were prepared from these two diamines with various commercially available aromatic dianhydrides via a one-step high-temperature polycondensation procedure. Most of these polyimides showed enhanced solubility in common organic solvents compared with those corresponding polyimides derived from 4,4′-ODA. Especially, polyimide derived from BTFP-ODA and rigid pyromellitic dianhydride (PMDA) was also soluble in DMF, DMAc, DMSO, NMP, and m-cresol at room temperature. These polyimides had inherent viscosities from 0.41 to 1.26 dLg⁻¹ in NMP or m-cresol at 30°C. Transparent, flexible, and tough films can be obtained by casting from their DMAc or m-cresol solutions. These films had the UV onset wavelengths in the range of 347-391 nm and the wavelengths at 80% transmission of 445-544 nm, indicating high optical transparency. They also exhibited good thermal stability with glass transition temperatures in the range of 260-327°C. The decomposition temperatures of these polyimides at 5% weight loss under nitrogen were 429-609°C. Because of the weak carbon-iodine bond, polyimides derived from DI-ODA decomposed at lower temperatures than polyimides derived from BTFP-ODA. The effects of the substituents at the 2 and 2′ positions of 4,4′-ODA on the properties of polyimides are also discussed. High optical transparency and good solubility combined with high thermal stability make these polyimides potential candidates for soft electronics applications.