Abstract
In view of cost reduction and environmental protection, achieving low dielectric constant (
k
value) at low fluorine content is of great significance. Incorporation of perfluorocyclobutyl (PFCB) aryl ether-containing side chains into polyimide, which is expected to impede compact stacking of polymer chains and increase the fraction of free volume (FFV) as a consequence, may be an effective strategy to reduce the
k
value of polyimide. A series of PFCB aryl ether-containing polyimides with various side chain lengths and side chain contents are produced. To our delight, a nearly state-of-art
k
value of 2.31 is achieved at a fluorine content of 23.8%, representing the highest efficiency of fluorine atom in reducing the dielectric constant of polyimide and confirming the effectiveness of side chain fluorine chemistry. Positron annihilation lifetime spectroscopy (PALS) and dual-processed weight change experiment results indicate that the dielectric constant of semi-fluorinated polyimide is determined by the opposite actions exerted by FFV and water absorption. Moreover, this kind of fluorine-containing polyimide is proved to be an eligible candidate for dielectric applications with excellent overall performance in dielectric constant as well as thermal stability and mechanical strength.