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:

• (1) 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.
• (2) 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/cm² sensitivity and a 5.5 γ value.