Synthesis Of Coumarin-based Oxime Ester Derivatives And Their Application In LED Photocuring

Photocurings technology has been widely used in various industrial applications including coatings, inks, adhesives and 3D printing due to its significant advantages such as low energy costs, high productivity, and temporal-spatial control. Compared to the traditional UV curing, photocuring employing light emitting diode(LED) as irradiation source features efficient energy utilization, minimal thermal effect and avoiding ozone generation. Photocuring formulations generally contain photoinitiators, reactive diluents, oligomers, and various addictives. A photoinitiator plays a key role in the photocuring formulation because its activity significantly affects the curing speed, the functionality conversion and the property of the end products. Until now, most photoinitiators have been specifically developed for UV curing and are not suitable to be used in LED photocuring. The aim of this project is to develop a series of efficient photoinitors through proper molecular design and systematic study on structure-property relationship.In the first section, four photoinitiators containing coumarin moieties as chromophores and oxime-ester groups as initiation functionalities were successfully prepared. The structures of the target product were comfired via nuclear magnetic resonance spectroscopy(NMR) and high resolution mass spectroscopy(HRMS). The new 2PIs O-4 and O-3 were designed to investigate the effect of different substituted positions on structure-reactivity relationship. O-3O and O-3F were prepared to study the impact of the electronic effect on the photophysical and photochemical behavior. Investigation on the photophysical properties of the initiators was conducted via UV-vis absorption and emission spectra, respectively. Photoinduced cleavage process of the initiators was proposed according to the steady-state photolysis experiments and ESR measurements. The photopolymerization kinetics under visible LED light were study via Fourier transform infrared spectroscopy(FTIR). Finally, the thermal stability of the investigated photoinitiators in the absence/presence of monomers was studied via thermal gravity analysis(TGA) and differential scanning calorimetry(DSC), respectively. The results indicated that: 1. the broad absorption band ranging from 400 to 480 nm makes the novel oxime-ester become attractive PIs for visible LED photopolymerization, especially for 450 nm LED light as a curing source; 2. The substitution position and the incorporation of electron donating/withdrawing groups considerably affected the absorption and emission as well as the initiation activity; 3. The investigated oxime-ester could effectively induce photopolymerization of acrylate monomers under 450 nm LED irradiation. O-3 exhibited the fastest photopolymerization rate and highest conversion. The initiation performance of O-3 was superior to the commercial oxime-ester initiator OXE-1. 4. The decomposition temperature in the absence/presence of monomers was 150 °C and 106 °C, indicating that the novel photoinitiator possesses sufficient thermostability.Considering that the diethylaminocoumarin moity can play the role of two-photon chromophore, two-photon excited fluorescence(TPEF) and two-photon structuring tests were performed to study the two-photon absorption cross section and two-photon initiation effciency. The results showed that the oxime-ester compounds exhibited sufficient two-photon absorption with the maximum cross section values ranging from 107 to 685 GM. In the two-photon polymerization structuring tests with acrylate formulations, the oxime-ester derivatives could be employed to build fine 3D microstructures. Moreover, the photoinitiators could also effectively initiate thiol-ene polymerization under two-photon excitation.In the second section, four photoacid generators(PAGs) containing sulfonate moity were designed and finally one novel PAG(PAG-1) were successfully prepared. The results indicated that under the irradiation of 405 LED light, the initiation ability of PAG-1 was low when using as unimolecular PAG. However, the photointiaton system containing PAG-1 and commercial iodonium salt enabled efficient ring-opening photopolymerization of the epoxy monomers.