Novel negative-type soluble photosensitive polyimides: Synthesis and characterization

In the present paper, we describe the synthesis and characterization of a novel negative-type soluble photosensitive polyimide (PSPI). A group of new photosensitive polyimides has been prepared by condensation of dianhydrides bearing photoreactive ester groups and aromatic diamines in N-methylpyrrolidone (NMP), followed by chemical imidization using acetic anhydride without acid accepters such as pyridine or triethylamine. Thus, the starting monomer used in the synthesis of a commercial aromatic polyimide has been chemically modified with four different photosensitive groups (chlorine-free synthesis). All the intermediates as well as the resulting polymers have been characterized. The PSPI esters were found to be soluble in N-alkyl-substituted amides. Their irradiation with UV light induces cross-linking of the photoreactive ester groups. These systems change from being weakly to being heavily cross-linked during irradiation and do not swell during development. The remaining PSPI esters do not require thermal imidization because they are already imidized, and shrinkage is about 20% due to volatilization of photoreactive groups.