Materials with low dielectric constant and loss and good thermal properties prepared by introducing perfluorononenyl pendant groups onto poly(ether ether ketone)

Abstract

A new monomer, 2,6-difluorophenyl-(4′-perfluorononenyloxy)phenyl-methanone (2F-PFN), was synthesized using a simple two-step reaction. A series of novel poly(ether ether ketone)s (PEEK-PFN-x) containing perfluorononenyl groups were then prepared from 2F-PFN, resorcin, and 4,4′-difluorobenzophenone by nucleophilic polycondensation. The resulting copolymers were found to have different electric and thermal properties depending on the molar ratio of perfluorononenyl groups. PEEK containing a 5% molar ratio of perfluorononenyl (PEEK-PFN-5) possessed an intrinsic low dielectric constant of 2.73 and low dielectric loss of 3.00 × 10⁻³ at 10 kHz. Another blended polymer prepared from PEEK and PTFE (PEEK/PTFE-5) possessed a dielectric constant of 3.21 and dielectric loss of 6.00 × 10⁻³ at 10 kHz. Therefore, PEEK/PTFE-5 had much higher dielectric loss than that of PEEK-PFN-5 with the same fluorine content. PEEK-PFN-5 also showed excellent thermal stability, with a 5 wt%-loss temperature of 436 °C. PEEK-PFN-5 showed a slight increase in hydrophobicity, with a water droplet contact angle of 89.7° compared with that of PEEK/PTFE-5 (86.4°) containing the same fluorine content as PEEK-PFN-5. Morphologies and fluoride distribution on the membrane surfaces were characterized by field emission SEM equipped with EDX. These results indicated that PEEK-PFN-5 possessed a more uniform distribution of fluorine on the membrane top surface than PEEK-PTFE-5.