Two types of novel fluorinated diimide-diacid monomers-[2,2 0 -(4,4 0 -(3 0 -methylbiphenyl-2,5-diyl)bis(oxy)bis(3-(trifluoromethyl)-4,1-phenylene))bis(1,3-dioxoisoindoline-5-carboxylic acid)] (III) and [2,2 0 -(4,4 0 -(3 0 -(trifluoromethyl)biphenyl-2,5-diyl)bis(oxy)bis(3-(trifluoromethyl)-4,1-phenylene))bis(1,3dioxoisoindoline-5-carboxylic acid)] (IV)-were respectively designed and prepared by the condensation of diamines I and II with two molar equivalents of trimellitic anhydride. From both diimide-diacids, two series of novel poly(amide-imide)s (PAIs) (IIIa-IIIe and IVa-IVe) bearing different pendant groups were prepared by direct polymerization with various aromatic diamines (a-e). All the PAIs had a high glass transition temperatures (T g s, 232-265 8C), excellent thermal stability (exhibiting only 5% weight loss at 493-542 8C under nitrogen) and good solubility in various organic solvents due to the introduction of the bulky pendant groups. The cast films of these PAIs (80-90 lm) had good optical transparency (73-81% at 450 nm, 85-88% at 550 nm and 87-89% at 800 nm) and low dielectric constants (2.65-2.98 at 1 MHz). The spin-coated films of these PAIs presented a minimum birefringence value as low as 0.0077-0.0143 at 650 nm and low optical absorption at the near-infrared optical communication wavelengths of 1310 and 1550 nm.

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