A new positive‐type photoreactive polyimide precursor using 1,4‐dihydropyridine derivative

A novel positive‐type polyimide precursor (BPDA/DDE) has been developed and examined. It is synthesized by the polycondensation of biphenyltetracarboxylic acid dianhydride and 4,4′‐diamino‐diphenyl ether, based on systems composed of dimethyl 1,4‐dihydro‐2,6‐dimethyl‐4‐(2‐nitrophenyl)‐3,5‐pyridinecarboxylate (nifedipine). Nifedipine photoconverted quantitatively to 4‐(2′‐nitrosophenyl)‐2,3‐dicarboxymethyl‐3,5‐dimethylpyridine (NDMPy) in a polyimide precursor film. It has been confirmed that nifedipine and NDMPy in the film act as a dissolution inhibitor and as a disolution promotor, respectively. The dissolution inhibition and promotion mechanisms were further investigated and subsequently expressed as follows: Dissolution inhibition is due to resistivity of the polyimide precursor to an alkaline aqueous solution through intermolecular hydrogen bonding between — COOH in the polymer structure and — NH — in nifedipine. Dissolution promotion is due to the hydrogen bond‐breaking by photoconversion from nifedipine to NDMPy and the newly formed intermolecular complex between the COOH and N in NDMPy. The photoreactive polyimide precursor (BPDA/DDE), including 25wt% nifedipine, shows a 170mJ/cm 2 sensitivity and a 5.5 γ value.