Thermally Stable, Organosoluble, and Colorless Poly(ether imide)s Having Ortho-Linked Aromatic Units in the Main Chain and Trifluoromethyl Pendent Groups

A novel series of aromatic poly(ether imide)s (PEIs) IVa-h containing ortho-linked aromatic units and pendent trifluoromethyl (CF 3 ) groups were prepared from 2,3-bis(3,4-dicarboxyphenoxy)naphthalene dianhydride (I) with various CF 3 -substituted aromatic bis(ether amine)s IIa-h via a conventional two-stage process including ring-opening polyaddition to form the poly(amic acid)s followed by either chemical or thermal imidization to the PEIs. The inherent viscosities of PEIs IVa-h were in the range of 0.43 -0.86 dL·g -1 that corresponded to weight-average and number-average molecular weights (by gel permeation chromatography) of 36000-73000 and 23000-51000, respectively. All the IV series were highly soluble in several organic solvents and could be solution-cast into transparent, flexible, and strong films. These films were essentially colorless; their cut-off wavelengths were between 368 and 377 nm and a very low b* value (a yellowness index) ranging from 4.1 to 5.5. They had useful levels of thermal stability associated with moderately high-glass transition temperatures (208-281 °C), 10% weight-loss temperatures in excess of 492 °C, and char yields at 800 °C in nitrogen higher than 51%. They also showed low water uptakes of 0.25-0.48% and low dielectric constants of 3.06-3.67 at 10 kHz. For a comparative study, a series of structurally similar, non-fluorinated PEIs Va-h from dianhydride I and bis(ether amine)s II'a-h were also prepared and characterized.