Synthesis and characterization of UV- and thermo-curable difunctional epoxyacrylates

This paper describes the synthesis and characterization of difunctional epoxyacrylate oligomers from the reaction of diglycidyl ether of bisphenol-A (DGEBA) and acrylic acid (AA) in the presence of triphenyl phosphine as catalyst. The reaction was investigated in situ by using Fourier transform-infrared spectroscopy in the temperature range of 60–120 °C, and demonstrated to be an addition esterification between the epoxide group and the carboxyl group. The specific rate constants calculated from the second-order kinetics obeyed Arrhenius law very well, and from which the activation energy was found to be 63.9 kJ mol−1. Moreover, various batches of respective epoxyacrylates, EA25 to EA100, were prepared by changing the equivalent ratio of carboxyl/epoxide from 0.25 to 1.0 in the feed under a temperature profile of 100 °C for 2 h and another 2 h at 120 °C. The epoxide conversions, acid values and epoxide equivalent weights of the produced EA25 to EA100 were all measured. The analysis by gel permeation chromatography revealed that the EA25 to EA75 consisted of unreacted DGEBA, monoacrylate-terminated epoxyacrylate and bisacrylate-terminated epoxyacrylate; while the EA100 was composed of only latter two. Increasing the initial carboxyl/epoxide equivalent ratio increased the epoxide conversion and the amount of bisacrylate-terminated epoxyacrylate. Yet, with an initial carboxyl/epoxide equivalent ratio of 0.5, the EA50 produced the maximum proportion (∼72%) of monoacrylate-terminated epoxyacrylate, which had one terminal double bond for UV-cure and one epoxide end group for thermo-cure. This dual-curable epoxyacrylate thus can be used as an adhesive sealant for LCD production.