Synthesis and characterization of highly-fluorinated colorless polyimides derived from 4,4′-((perfluoro-[1,1′-biphenyl]-4,4′-diyl)bis(oxy))bis(2,6-dimethylaniline) and aromatic dianhydrides

The authors report the synthesis and characterization of a polyimide (PI) series derived from 4,4′-((perfluoro-[1,1′-biphenyl]-4,4′-diyl)bis(oxy))bis(2,6-dimethylaniline) (8FBPODMA). The 8FBPODMA monomer containing a perfluorobiphenyl group with two 2,6-dimethylaniline units connected by an ether bond was synthesized and polycondensed with several aromatic dianhydrides, including 4,4′-biphthalic anhydride (BPDA), 4,4′-oxydiphthalic anhydride (ODPA), pyromellitic dianhydride (PMDA), and 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), by the traditional two-step imidization procedure. All PIs shows high optical transparency, higher than 80% at 500 nm for a thickness of ca. 10 μm and good thermal properties. The thermal decomposition temperatures (T_10%) of the PIs are in the range of 507-527 °C and the glass transition temperatures (T_g) are in the range of 280-345 °C. In addition, the PIs have low refractive indices because of their high fluorine contents. In particular, 8FBPODMA-6FDA shows a very low refractive index (1.5389) and a low birefringence (0.0054) at 637 nm.