Biobased and Colorless Polyimides With High Biomass Content and Transparency Derived From Camphor‐Based Alicyclic Diamines

ABSTRACT

Polyimides (PIs) are widely used as advanced substrates due to their excellent thermal and mechanical properties. However, conventional petroleum‐based aromatic PIs suffer from intrinsic coloration arising from charge‐transfer complex (CTC) formation, limiting their optoelectronic applications. In this study, two camphor‐derived alicyclic diamines (CA and CM) were synthesized, along with a reference isosorbide‐derived diamine (IS). These monomers were polymerized with 1,2,3,4‐cyclobutanetetracarboxylic dianhydride (CB) and a tetracarboxylic dianhydride featuring a cyclopentanone bis‐spironorbornane structure (Cp) to prepare six biobased CPIs. Their favorable optical transparency arises from the combined contribution of the non‐conjugated dianhydride structures and the alicyclic camphor‐derived diamine structures. The structure–property relationships of the biobased CPIs were systematically investigated. The CA series exhibits limited film‐forming ability because of its highly rigid molecular structure. In contrast, incorporating a methylene spacer into the CM series enhanced chain flexibility, leading to improved film‐forming ability and overall film quality. Among the prepared CPIs, CM–CB exhibited the most balanced performance, achieving 60% biomass content, optical transparency ( T ₄₀₀  = 82% and YI  = 3), and a glass transition temperature above 300°C. These results suggest that camphor‐derived diamines can serve as useful biobased units for developing CPIs with balanced optical transparency and thermal properties.