Soluble, colorless and biobased polyimides with high thermal stability derived from renewable anethole

Abstract

The development of soluble biobased polyimides is indispensable for their sustainable processing and applications. In this work, a novel diamine monomer (called DAN) containing an all-trans substituted cyclobutane segment, with a unique dihedral angle of 93.2°, was designed and synthesized from renewable anethole. DAN was then allowed to be polymerized with typical dianhydrides (ODPA, 6FDA and BPADA) to prepare linear polyimides via chemical imidization reactions. The obtained polyimides exhibited good solubility and processability and were easily casted into flexible polymer films and reprocessed through a casting–dissolving cycle. Since the charge transfer was greatly inhibited by introducing this all-trans substituted cyclobutane structure, all of these polyimides showed high transparency and appeared almost colorless. Transmittances of polyimide films at 450 nm were up to 85% with a low yellow index of about 7.17. In particular, these polyimides with highly twisted backbones exhibited low refractive indices and birefringence (0.0056–0.0116). Moreover, these biobased polyimides showed high thermal stability, with 5% weight loss at a temperature up to 520 °C and a glass transition temperature up to 300 °C. All these results indicate that this work provides high-performance biobased polyimides for sustainable applications in optical areas.