Colorless And Transparent Semi-Alicyclic Polyimide Films With Intrinsic Flame Retardancy Based On Alicyclic Dianhydrides And Aromatic Phosphorous-Containing Diamine: Preparation And Properties

Semi-alicyclic colorless and transparent polyimide (PI) films with intrinsically flame-retardant features, excellent optical transparency, and good thermal stability have been designed and successfully prepared. For this target, an aromatic diamine with lateral diphenylphosphine oxide substituent, 2,5-bis[(4-aminophenoxy)phenyl]diphenylphosphine oxide (BADPO) was polymerized with two alicyclic dianhydrides, including hydrogenated pyromellitic dianhydride (HPMDA) and hydrogenated 3,3 ',4,4 '-biphenyltetracarboxylic dianhydride (HBPDA), respectively, via a one-step high-temperature polycondensation procedure to afford two PIs, PI-a (HPMDA-BADPO), and PI-b (HBPDA-BADPO). The derived PI films maintained the intrinsic good properties for semi-alicyclic PI films, including excellent optical transparency in the ultraviolet-visible light region with the cutoff wavelength (lambda(cut)) around 322 nm and optical transmittance at the wavelength of 450 nm (T-450) higher than 83.0%. In addition, the PI films exhibited good thermal stability with the 5% weight loss temperatures (T-5%) higher than 460.0 degrees C and glass transition temperatures (T-g) higher than 235.0 degrees C. More importantly, the developed PI films exhibited intrinsic flame retardancy with the limited oxygen indices (LOI) of 41.1% for PI-a and 28.8% for PI-b. What is more, the PI films showed the flame retardancy class of UL94 VTM-0 and low thermal energy and smoke release during combustion.