Synthesis of an Aliphatic Dianhydride Monomer and Its Colourless, Low Dielectric Constant Aliphatic Polyimides

An aliphatic dianhydride containing amide functionality (–NCOCH₃), ethylenediamine-N,N '-disuccinic acid anhydride (EDSA) was synthesized via base catalyzed N-alkylation of aspartic acid with 1,2‑dibromoethane followed by dehydration of the N-alkylated product with Ac₂O and pyridine. Four aliphatic polyimides (API) were prepared via two-step condensation polymerization of EDSA with four diamines (three straight chain aliphatic diamines and one alicyclic diamine). The polyimide film of EDSA with 4,4′-methylene bis(2-methyl cyclohexylamine) was almost colourless (cut of wavelength λ₀ = 312 nm and transmittance > 90% in the range of 450–800 nm). T₁₀ (temperature of 10% weight loss) of API were in the range of 417–457°C and T_g of 149–178°C. The API films exhibited low dielectric constants of 2.31–2.92 at 1 MHz.