Synthesis and Characterization of Photosensitive Epoxy Resin Containing Dual Functionality in the Main Chain for Negative Photoresist Applications

Abstract

Photosensitive polymers have received considerable attention in the recent past owing to their applications as photoresists to make integrated circuits, photocurable coatings, photorecorders, printing plates, optical memory devices and energy exchange materials. Polymers employed for these applications should possess one of the photoreactive groups like cinnamoyl, coumaroyl, azide, arylidene, cyclic carbonate and stilbene. The photosensitivity of these materials is mainly based on the electron density of the photoactive chromophore. Photoresist materials are of two kinds: positive and negative photoresists. Positive photoresists become soluble in developers on exposure to UV light. In negative photoresists, the photochemistry that occurs on irradiation renders the material less soluble in the developer; the unirradiated parts of the coating are washed away and a negative polymer image of the original pattern remains on the substrate. Among many -unsaturated ketones received greater attraction due to their high sensitivity towards UV radiation. Most of the photosensitive polymers reported in the literature possess poor solubility in common organic solvents and have high softening temperatures. Nevertheless, further research is necessary to develop new polymers with structural modifications in order to enhance the desirable properties and applications.The photosensitive monomers, 3-(4-hydroxy-3-methoxyphenyl)-1-(4-hydroxyphenyl) propenoneand 1, 3-bis (4-hydroxyphenyl) propenone ivwere prepared respectively by refluxing 3-methoxy-4-hydroxybenzaldehyde and 4-hydroxybenzaldehyde with 4-hydroxy acetophenone using borontrifluoride diethyletherate catalyst. 2,6-Bis(4-hydroxy-3-methoxybenzylidene)cyclohexanone, 2,6-bis(4-hydroxybenzylidene) cyclohexanone were prepared respectively by refluxing4-hydroxybenzaldehydeand 3-methoxy-4-hydroxybenzaldehyde with cyclohexanone. Bis (4-hydroxy-3-methoxy benzylidene) acetone was prepared from 4-hydroxy-3-methoxy benzaldehyde and acetone. The structure of the monomers was confirmed by FT-IR, 1H and13C-NMR spectroscopic techniques.In the present investigation, photosensitive polymers were prepared by reacting the monomers 3-(4-hydroxy-3-methoxyphenyl)-1-(4-hydroxyphenyl) propenone, 1, 3-bis (4-hydroxy phenyl) propenone, 2, 6-bis (4-hydroxy-3-methoxy benzylidene) cyclohexanone, 2, 6-bis (4-hydroxy benzylidene)cyclohexanone and bis-(4-hydroxy -3-methoxy benzylidene) acetone with epichlorohydrinby solution polycondensation method. All the polymers were characterized systematically.The reaction conditions and molar ratio of diol and epichlorohydrin were optimized.The synthesized polymers were characterized by UV, FT-IR, 1H and 13C -NMR spectroscopic techniques. The photosensitive property of the polymers in film and solution state was studied. The effect of solvents, photoinitiators, sensitizersand temperature on photoreactivity were investigated by ultraviolet spectroscopy. Curing kinetics of the synthesized epoxy resin was determined by differential scanning calorimetry technique.