Synthesis and chemically amplified photo-cross-linking reaction of a polyimide containing an epoxy group

A new polyimide, PI(6FDA/ep-AHHFP), containing an epoxy group was synthesized by the reaction of epichlorohydrin with PI(6FDA/AHHFP), which was prepared from 4,4'-(1,1,1,3,3,3-hexafluoro-2-propylidene)diphthalic anhydride (6FDA) and 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (AHHFP) in the presence of benzyl(trimethyl)ammonium chloride at 110-120 degrees C. This polyimide having an epoxy group is highly soluble in most common solvents. Photochemical reactivity of PI(6FDA/ep-AHHFP) was examined in the presence of diphenyliodonium hexafluoroarsenate as an acid generator. The conversion and the curing rate were determined by the absorbance change in the IR band at 905 cm(-1) for the epoxy group. The activation energy for cross-linking reaction of PI(6FDA/ep-AHHFP) was found to be similar to 6 kJ/mol. The reaction radius of an acid in PI(6FDA/ep-AHHFP) containing diphenyliodonium hexafluoroarsenate as a photoacid generator was determined to be about 19-30 Angstrom in the chemical amplification process when heated for 5-40 min at 50-195 degrees C. The quantum yield for cross-linking of PI(6FDA/ep-AHHFP), Phi(gel), obtained from the characteristic curve was 3.0. The sensitivity, D-gel, and contrast, gamma, after postcure at 100 degrees C for 30 min were 4.8 x 10(-10) einstein cm(-2) and 5.7, respectively. The quantum yield for cross-linking, Phi(GPC), was determined to be 2.6 from gel permeation chromatography measurements.