Soluble polyimides containing 1,4:3,6‐dianhydro‐d‐glucidol and fluorinated units: Preparation, characterization, optical, and dielectric properties

Aiming to develop soluble and colorless polyimides, two novel diamines, 2,5‐bis(2‐trifluoromethyl‐4‐amino‐phenoxy)‐1,4:3,6‐dianhydrosorbitol (2a) and 2,5‐bis(2‐methyl‐4‐amino‐phenoxy)‐1,4:3,6‐dianhydrosorbitol (2b), were designed and synthesized by the reduction of corresponding dinitro monomer which was obtained via solvent‐free melt heating method. Polyimides (PI–(1–5)) containing 1,4:3,6‐dianhydro‐ d ‐glucidol fragments were prepared from 2a and five kinds of common dianhydrides and PI–6 was synthesized from 2b and 4,4′‐(hexafluoroisopropylidene)‐diphthalic anhydride (6FDA) via a two‐step thermal imidization. All the polyimides were readily soluble in common polar solvents and could afford flexible, tough, and transparent films with transparency as high as 87% at 450 nm. Meanwhile, PI–(1–6) exhibited unexpectedly low dielectric constants of 2.02–2.52 at 1 MHz. In addition, analogs PI–7 derived from 2,5‐bis(4‐amino‐phenoxy)‐1,4:3,6‐dianhydrosorbitol (2c) and 6FDA and PI–8 derived from 4,4′‐bis(4‐amino‐2‐trifluoromethylphenoxy)biphenyl (2d) and 6FDA were also obtained via a two‐step thermal imidization for comparision with PI–(1–6) on aspects of thermal, mechnical, optical, electrical, and morphological properties. The structure–property relationships of PI–(1–8) were discussed in detail.