Synthesis and properties of low-surface-energy polyimides

An aromatic diamine monomer, 1H,1H-perfluorooctyl 3,5-diaminobenzoate (PFD), was synthesized in three steps, which was used to prepare the polyimides containing pendant perfluoroalkyl chains via the polymerization of PFD with commercial 4,4′-(hexafluoroisopropylidene)diphthalic anhydride. Various characterization techniques including thermogravimetric analysis, infrared spectroscopy, and X-ray photoelectron spectroscopy were used to characterize the new polyimides with perfluoroalkyl chains. The resulting polyimide film exhibits hydrophobicity with a contact angle of 95° for water, and the calculated surface free energy is 37.4mNm^-1. Superhydrophobic surfaces were also demonstrated by coating the polyimide containing pendant perfluorooctyl chains on rough alumina substrate.