Synthesis and properties of organosoluble polyimides derived from 2,20-dibromo- and 2,20,6,60-tetrabromo-4,40-oxydianilines

摘要

Two new aromatic diamines, 2,2′-dibromo4,4′-oxydianiline (DB-ODA 4) and 2,2′,6,6′-tetrabromo-4,4′-oxydianiline (TB-ODA 5), have been synthesized by oxidation, bromination, and reduction of 4,4′-oxydianiline (4,4′-ODA). Novel polyimides 6a-f and 7a-f were prepared by reacting DB-ODA (4) and TB-ODA (5) with several dianhydrides by one-step method, respectively. The inherent viscosities of these polyimides ranged from 0.31 to 0.99 dL/g (0.5 g/dL, in NMP at 30°C). These polyimides showed enhanced solubilities compared to those derived from 4,4′- oxydianiline and corresponding dianhydrides. Especially, polyimides 7a, derived from rigid PMDA and TB-ODA (5) can also be soluble in THF, DMF, DMAc, DMSO, and NMP. These polyimides also exhibited good thermal stability. Their glass transition temperatures measured by thermal mechanical analysis (TMA) ranged from 251 to 328°C. When the same dianhydrides were used, polyimides 7 containing four bromide substituents had higher glass transition temperatures than polyimides 6 containing two bromide substituents. The effects of incorporating more polarizable bromides on the refractive indices of polyimides were also investigated. The average refractive indices (n_(av)) measured at 633 nm were from 1.6088 to 1.7072, and the in-plane/out-of-plane birefringences (Δn) were from 0.0098 to 0.0445. It was found that the refractive indices are slightly higher when polyimides contain more bromides. However, this effect is not very obvious. It might be due to loose chain packing resulted from bromide substituents at the 2,2′ and 2,2′,6,6′ positions of the oxydiphenylene moieties.