Synthesis and Properties of Novel Polyimides Containing Fluorinated Alkoxy Side Groups

A novel method for the preparation of a fluorinated aromatic diamine was investigated. This new diamine contains a fluoroalkoxy (C6F13—C2H4—O—) side chain and it was synthesised by the reaction of 1H,1H,2H,2H-perfluorooctanol with 2-(4-nitrophenoxy)-4-nitrophenol via the Mitsunobu reaction and subsequent reduction. This novel diamine was used with different dianhydrides, 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), pyromellitic dianhydride (PMDA) and benzophenonetetracarboxylic dianhydride (BTDA) to prepare polyimides by direct thermal imidization. The polyimide properties such as inherent viscosity, solubility, thermal and surface properties were investigated to illustrate the contribution of the fluoroalkoxy group that is attached to the polyimide backbone. The resulting polyimides possessed good thermal properties, the presence of the fluoroalkoxy group did not affect the thermal stability and increased the solubility in common organic solvents. The glass transition temperatures (Tg) of the fluorinated polyimides were higher than 195°C. The surface tension determined by contact angle measurements of the polyimide prepared with dianhydride 6FDA and diamine containing fluorinated alkoxy side group was 25.3 mN·m–1.