Synthesis and properties of fluorinated polyimides with multi-bulky pendant groups

A new aromatic diamine monomer, 2,2′-bis[3,5-di(4-trifluoromethylphenyl)-4-(4-aminophenoxy)phenyl]sulfone, containing four pendant trifluoromethylphenyl group substituents was successfully synthesized via a three-step reaction from readily available reagents. A new series of fluorinated polyimides with multi-bulky pendant groups was prepared from the diamine monomer with three commercially available aromatic tetracarboxylic dianhydrides using one-step high-temperature polycondensation. The incorporation of multi-bulky pendant fluorinated groups and large non-coplanar structures brought about a great improvement in their properties. The resulting polyimides had excellent solubility and the maximum solubility even reached 20 wt% in NMP, CHCl3, and THF at room temperature. Their film displayed a light color and high optical transparency with the cut-off wavelengths ranging from 327 to 343 nm. They also possessed intrinsically low dielectric constant values of 2.69–2.85 (at 1 MHz) and low water absorption (0.59–0.68%). Moreover, these polyimides showed high glass transition temperatures (259–281 °C) and excellent thermal stability with 5% weight loss at temperatures over the range of 551–561 °C and 515–520 °C under nitrogen and air atmospheres, respectively. Compared to some trifluoromethyl-substituted polyimides, these polyimides with multi-bulky pendant groups possessed better solubility and lower cut-off wavelength and dielectric constants.