Synthesis and properties of fluoro-polyetherimides

A series of amorphous fluoro-polyetherimides based on 2,2′-bis(3,4-dicarboxyphenyl) hexafluropropane dianhydride (6FDA) and di-ether-containing diamines 4,4′-bis(3-aminophenoxy)diphenyl sulfone (m-SED), 4,4′-bis(4-aminophenoxy)diphenyl sulfone (p-SED), 4,4′-bis(4-aminophenoxy)diphenyl propane (BPADE) were synthesized. These melt processable polyetherimide polymers from p-SED and BPADE showed excellent electrical properties. The dielectric constants, 2.74 and 2.65 at 10 MHz respectively, are lower than commercially available polyetherimide ULTEM 1000, and polyimide Kapton H films. In addition, we found that trifluoromethyl groups-containing polyimides not only show extraordinary electrical properties, but they also exhibit excellent long-term thermo-oxidative stability and reduced water absorption relative to non-fluorinated polyimides. The weight retention of these fluoro-polyetherimides at 315°C for 300 h in air varies from 93% to 98%. Whereas, their moisture absorption at 100 RH at 50°C was in the range of 0.3% to 1.05%, which is much lower than those of Ultem 1000 and Kapton H. In the case of fluoro-polyetherimides from p-SED and m-SED (para and meta isomers) diamines with 'ether' and sulfonyl (-SO₂) spacer groups, the d-spacing and T_g values decreased from 4.72 angstrom to 4.56 angstrom and 293°C to 244°C respectively. Similarly, the transparency of these polymer films (in the range of 80% to 90%) at 500 nm solar wave-length was higher than Ultem 1000 and Kapton H.