Investigation on dual functional epoxy resins containing photosensitive group in the main chain for photoresist applications

Dual functional photosensitive epoxy resins were synthesized by solution polycondensation of 1,3-bis(4-hydroxyphenyl)propenone (BHPP) and 3-(4-hydroxy-3-methoxyphenyl)-1-(4-hydroxyphenyl)propenone (HMPHPP) with epichlorohydrin. The characterization of synthesized epoxy resins comprised Fourier transform infrared (FTIR) spectroscopy, 1H-NMR, and 13C-NMR spectroscopic techniques. The thermal properties of the epoxy resins were studied by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) under a nitrogen atmosphere and found that the synthesized resins were stable up to 300 °C. The effect of curing agents diaminodiphenylsulfone (DDS) and diaminodiphenylmethane (DDM) on the thermal stability of epoxy resin was compared and found that DDS cured epoxy resin has higher thermal than DDM. The photocrosslinking properties of the epoxy resins were studied with UV-Visible spectroscopy, and we observed that the olefinic double bond undergoes 2π-2π cycloaddition and leads to cyclobutane ring. Also, the effect of solvents on the photocrosslinking of the epoxy resin was also studied. Solvents with higher polarity favored the 2π-2π cycloaddition. The dual functionality of the resins was confirmed by FTIR study. The storage stability of the synthesized epoxy resins remained over more than 60 days. The synthesized epoxy resins successfully applied as negative photoresists.