Synthesis, Photochemistry And Photopolymerization Of Thioxanthone Dicarboxamide Derivatives

Photopolymerization is widely used in many industries such as printing ink, coating, adhesive and etc. because of its excellent characteristics of low polymerization temperature, high polymerization rate and easy control. And research of photoinitiators is the key in photopolymerization development.Three types of thioxanthone dicarboxamide derivatives were designed and synthesised to reach the goal of high efficiency and low energy consumption, they are 4-((1,3,6-trioxothiochromeno[2,3-e]isoindol-2(1H,3H,6H)-yl)methyl)cyclohexanecarboxylic acid(TX-COOH), 2-(2-hydroxyethyl)thiochromeno[2,3-e]isoindole-1,3,6(2H)-trione(TX-OH) and 2-(2-mercaptoethyl)thiochromeno[2,3-e]isoindole-1,3,6(2H)-trione(TX-SH). Multiple steps to synthesis 1H-thioxantheno[4,3-c]furan-1,3,6-trione with raw materials such as thiosalicylic acid, nitrophthaldiamide, sodium hydroxide, polyphosphoric acid, acetic anhydride and etc.. Amidation reactions were carried out to introduce carboxyl, hydroxyl and sulfydryl to synthesis the three thioxanthone dicarboxamide derivatives. Structures of the products were characterized by 1H NMR, FT-IR and elemental analysis. Results confirm the expected structure. Thermal stabilities were measured by TG. Results showed four derivatives have good thermal stability for storage.Photochemistry of three thioxanthone dicarboxamide derivatives were investigated. UV-Vis spectrums showed effective absorption wavelength shift in the direction of visible light after the introduction of carboxyl, hydroxyl and sulfydryl. The maximum ultraviolet absorption were 284 nm, 280 nm and 283 nm, and maximum absorption wavelength were 414 nm, 404 nm and 417 nm. Photochemical reactions of derivatives were monitored by UV-Vis together with UV point light source. Results indicated that all synthesized derivatives were photolyzed after UV irradiation with light intensity of 120 mW/cm2.Compared to isopropyl thioxanthone, photopolymerization properties were studied by monitor the convention of C=C of TPGDA by Real-FTIR. Investigate whether thioxanthone dicarboxamide derivatives can match co-initiator EDAB to increase efficiency of initiation by the addition of EDAB. Results showed photopolymerization of thioxanthone structure can effectively enhanced by the induction of carboxyl, hydroxyl and sulfydryl. And the participation of EDAB would increase photopolymerization performance by times.