Photosensitive poly(benzoxazole) via poly(o-hydroxy azomethine) II.: Environmentally benign process in ethyl lactate

The synthesis and photosensitivity of poly(o-hydroxyazomethine) (PHAM) from isophthalaldehyde (IPA) and 4,4'-(hexafluoroisopropylidene)bis(o-aminophenol) (6FAP) in an environmentally friendly solvent, ethyl lactate (EL) was investigated. Polycondensation of IPA and 6FAP proceeded in EL, giving PHAM with a number average molecular weight more than ten thousands. The solution of PHAM in EL showed a good stability for hydrolysis. The photosensitive film cast from the solution of PHAM and 25 wt % 1-{1,1-bis[4-(2-diazo-1-(2H)-naphthalenone-5-sulfonyloxy)phenyl]methylethyl}benzene (S-DNQ) in EL showed a sensitivity (DO) of 250 mJ/cm(2) and a contrast (gamma(0)) of 2.5 with 436 nm light (g-line), respectively. A fine positive image featuring 10 pm line-and-space pattern was observed on the film of the photoresist exposed to 200 mJ/cm(2) of g-line by the contact-printing mode. The positive image was successfully converted to a poly(benzoxazole) (PBO) pattern by thermal treatment. The optically estimated dielectric constant of the PBO is 2.76.