Simultaneously Improving Dielectric and Mechanical Properties of Crown Ether/Fluorinated Polyimide Films with Necklace-Like Supramolecular Structure

A necklace-like supramolecular structure is constructed from 18-crown ether-6 (18CE6) as the host molecule and fluorinated polyimide (FPI) as the guest molecule to enhance the mechanical properties as well as to further lower the dielectric constant of FPI. The introduction of 18CE6 simultaneously enhances the stiffness and toughness of FPI films. In particular, the elongation at break is increased by over 200%. Furthermore, the dielectric constant of FPI films with 40 mol% 18CE6 is decreased to 2.74 from 3.15 of pure FPI, which is attributed to the enlarged free volume by the necklace-like supramolecular structure of 18CE6/FPI. Accordingly, the glass transition temperature of 18CE6/FPI films is slightly reduced to 305 °C, which is still high enough during the soldering process for the preparation of flexible copper clad laminate. In addition, the water absorption of FPI films is gradually decreased to 0.52% as the loading of 18CE6 raises to 40 mol%, representing the excellent moisture resistance of 18CE6/FPI films.