Quaternary copolyimides with various monomer contents: Thermal property and optical transparency

Several quaternary copolyimides (Co-PIs) were prepared using various molar ratios of two dianhydrides and two diamines: 4,4’-(hexafluoroisopropylidene) diphthalic anhydride (6FDA), 1,2,4,5-benzenetetracarboxylic dianhydride (pyromellitic dianhydride) (PMDA), 2,2’-bis(trifluoromethyl)benzidine (TFB), and trans -1,4-cyclohexanediamine (CHDA). Copolymerization of the monomers afforded poly(amic acid)s (PAA), which were solution-cast onto glass plates and subjected to thermal imidization to yield the Co-PI films. These Co-PI films showed no significant decomposition below 500 °C in a N 2 atmosphere. Finally, the films were colorless and exhibited high optical transparencies, with UV-vis. absorption edges of 342-367 nm and low yellow index (YI) values of 1.72–5.09.