Synthesis and Properties of UV/Vis-LED Excitable Photoinitiators Based on Coumarin Pyridinium Salt

Three novel pyridinium salt photoinitiators(PIs),which can be excited by ultraviolet/visible light emitting diode(UV/Vis-LED),based on coumarin framework were designed and synthesized,and their structure activity relationship and photoinitiation activities as one-component radical photocuring initiators in acrylate system were studied. UV-Vis absorption spectra showed that the three PIs have strong absorption in the region of 300-400 nm. The steady-state photolysis and photopolymerization kinetics of three PIs were studied under the irradiation of LED@365 nm and LED@405 nm light sources. The results indicated that the three PIs all demonstrate good photoly. sis rate and excellent initiation activity for acrylates. Through the study of structure-activity relationship,it is found that when the electron-pushing methoxy group is introduced into the para-position of the pyridine ring,the activity of initiating the polymerization of acrylate monomers will decrease;meanwhile,the activity will increase while the electron-withdrawing acetyl group is introduced into the para-position of the pyridine ring. Differential scanning calorimetry(DSC) experiments indicated that the three pyridinium onium salt photoinitiators all demonstrate excellent thermal stability. It is interesting that when PIs were mixed with acrylic monomers,the thermal stability of the system can be improved. The generation of active species was proved by electron spin resonance(ESR)and the initiation mechanism of the initiator was discussed.