Low-dielectric polyimide resins with improved processability and thermal properties

In this work, a series of fluorene-based polyimide resins with pendent and endmost phenylethynyl groups were synthesized using 9,9-Di[4-(3,4-dicarboxyphenoxy)phenyl]-4,5-diazafluorene dianhydride (BPF-PA) and aromatic diamines ((3,5-diaminophenyl) (4-(phenylethynyl)phenyl)methanone (DPEB), 4,4′-oxydianiline (4,4′-ODA)), 4-phenylethynylphthalic anhydride (4-PEPA) as the end-capping reagent. The chemical structure, thermal properties, solubility, and melt flow behavior of the imide oligomers were characterized using Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), solubility test, and rheological measurement. The imide oligomers showed high solubility in the low-boiling solvents and low melt viscosity due to their flexible, sterically hindered side-chain and cardo architectures. The thermal properties, mechanical properties, and dielectric properties of the thermosets derived from the imide oligomers were studied using thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), thermomechanical analysis (TMA), mechanical testing, and dielectric performance testing. The cured resins exhibited outstanding dielectric property in the range of 18–40 GHz involving a dielectric constant (D k ) as low as 2.99 and a dielectric loss (D f ) as low as 0.0017 while possessing high thermal decomposition temperature up to 569°C and glass transition temperature up to 345°C. Additionally, the thermosets displayed good mechanical properties, dimensional stability and low water absorption. The obtained polyimide resins exhibited exceptional comprehensive properties, indicating their great potential as matrix resins in the applications of heat resistant, wave transparent composites for the aerospace industry.