Synthesis and Characterization of Negative-Type Photosensitive Polyimides Based on Cyclobutane-1,2,3,4Tetracarboxylic Dianhydride

A series of negative-type photosensitive polyamic acids (PAAs) with various molecular weights was synthesized from cyclobutane-1,2,3,4-tetracarboxylic dianhydride, 2-(methacryloyloxy)ethyl-3,5-diaminobenzoate, and 2-(methacryloyloxy)ethyl-4-aminobenzoate in N-methyl-2-pyrrolidone. We investigated the degree of planarity, transmittance, and thermal stability for the PAAs after the photoirradiation reaction at an exposure dose of 200 mJ/cm2. The films prepared from the PAA with the lowest molecular weight (PAA-1) exhibited a higher degree of planarity and transmittance compared with those of the film prepared from the PAA with the highest molecular weight (PAA-4). The initial decomposition temperatures of the cured PAAs with different molecular weights were similar and were stable up to around 300DGC. Further, the photosensitivity and transmittance of PAA-1 were investigated in the presence of photoinitiators at 365-400 nm with a high-pressure mercury lamp. The resolution of the photocured film was about 50 mm.