Polyimide/Crown Ether Composite Films with Necklace-Like Supramolecular Structure and Improved Mechanical, Dielectric, and Hydrophobic Properties

The strong interchain packing and polarity of polyimide (PI) compromise its outstanding thermal and mechanical properties. Crown ethers are theoretically expected to form host–guest inclusion complex with PI and improve its disadvantages. On the basis of this hypothesis, we synthesized a series of PI/crown ether composite films and investigated their synthesis mechanism, structures and properties. Our results suggest that the introduction of crown ethers increased the free volume of PI matrix and generated a special necklace-like supramolecular structure, which simultaneously and greatly improved PI’s mechanical, dielectric and hydrophobic properties. The Young modulus, elongation and tensile energy at break of PI composite films were maximally increased by 73.0%, 135.5%, and 190.0%, respectively. Meanwhile their dielectric constant and water absorption were minimized by 16.6% and 66.8%, respectively. Crown ethers with different molecular sizes demonstrated different improvement effects on PI’s properties. Their inclusion rates stabilized at ∼50%, which are related to the equal reaction probability between anhydride and amino groups.