3,5-diaminobenzoic acid: a simple method to improve the solubility and lithography accuracy of photosensitive polyimides

Traditional polyimides (PI) have poor solubility in common organic solvents due to the high rigidity of the main chain and strong intermolecular forces. Consequently, the traditional negative photosensitive polyimides (PSPIs) processing needs to use a large amount of DMF, NMP and other toxic organic solvents to dissolve the poly(amic acid) (PAA), which causes the problems of volatile organic compounds emission, difficult recovery and high cost. With increasing environmental concerns, it is essential to fundamentally address the solubility limitations of PIs to reduce their dependence on hazardous solvents and improve environmental compatibility. 3,5-diaminobenzoic acid (DABA) was used to improve the solubility of PI. The carboxyl groups in DABA molecules were introduced as pendant groups along the PI main chains, which greatly increased the polarity of the polymer and provided more reactive sites for the photosensitive compound, thus significantly improving the solubility of PAA in a milder and more environmentally friendly solvent system. In this study, a series of photosensitive poly(amic acid) (PSPAA) samples with varying DABA contents were synthesized. The structure, mechanical properties, thermal properties, and morphology of PI were investigated by FTIR, DMA, TGA, and SEM, respectively, through which the optimal DABA ratio was obtained.