Synthesis and positive-imaging photosensitivity of soluble polyimides having pendant carboxyl groups

Polyimides having pendant carboxyl groups were prepared by a direct one-pot polycondensation of 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) with 3,5-diaminobenzoic acid (DABz) and bis[4-(3-aminophenoxy)phenyl]sulfone (m-BAPS) in the presence of a γ-valerolactone/pyridine catalyst system using N-methyl-2-pyrrolidone (NMP)/toluene mixture as a solvent at 180 °C. The obtained polyimides were soluble in dipolar aprotic solvents such as dimethylformamide, dimethyl sulfoxide, and NMP as well as in tetrahydrofuran and aqueous basic solution. The solubility of the polyimides was dependent on the diamine composition. Photosensitve polyimide (PSPI) systems composed of the polyimides and diazonaphthoquinone compound as a photosensitive material gave positive-tone behavior by UV irradiation, followed by development with aqueous tetramethylammonium hydroxide (TMAH) solution. The scanning electron microscopic photograph of the resulting image showed 10-μm line/space resolution with about 15 μm of film thickness. The PSPIs baked at 350 °C for a short time had excellent thermal resistance comparable to the original polyimides.