Two new perfluorodecylthio substituted aromatic diamines, namely 2,4-diamino-1-(1H,1H,2H,2H-perfluorodecathio)benzene (DAPFB) and 2,2'-Bis((1H,1H,2H,2H-perfluorodecyl)thio)[1,1'-biphenyl]4,4'-diamine (BPFBD) were synthesized and polycondensed with 4,4'-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) to produce two new perfluorinated polyimides (PI2 and PI4). The chemical structures of these polyimides were confirmed by Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopy and elemental analysis. Two other polyimides (PI1 and PI3) were also synthesized from 6FDA and analogous perfluorodecylthio unsubstituted diamines to investigate the incorporation effect of perfluorodecylthio group on various physical and chemical properties of the synthesized PIs. Compared with PI1 and PI3, PI2 and PI4 exhibited improved solubility, optical transparency, and hydrophobicity, lower moisture absorption, dielectric constant, and thermo-mechanical stabilities owing to the presence of the perfluorodecylthio side group in the polymer chain. Even though thermo-mechanical properties of PI2 and PI4 ( T5d: 413 and 404 °C, Tg: 220 and 209 °C, tensile strength of 101 and 76 MPa, tensile modulus of 1.7 and 1.5 GPa and elongation at break of 8 and 10%, respectively) were reduced in comparison to PI1 and PI3 but still were good enough for most of the practical applications. Most importantly, the presence of the perfluorodecylthio side group in BPFBD considerably reduced the dielectric constant of PI4 to 2.71 which was quite low as aromatic polyimide.
Tapaswi, Pradip Kumar, Myeon-Cheon Choi, Saravanan Nagappan, Chang-Sik Ha
J. Polym. Sci. Part A: Polym. Chem.