| Due to the advantages of low environmental pollution and fast speed,photocuring technology has been widely used in the technical fields of radiation curing,microelectronics and additive manufacturing.In the composition of the photocuring system,the photoinitiator(PIS)determines the photocuring mechanism,radiation light source,photocuring speed,and properties of the material after photocuring.Norrish type ? photoinitiator can directly initiate polymerization through cleavage reaction to generate active radicals,and it is an ideal type of photoinitiator because it does not require co-initiation of amine hydrogen donor.The currently commercialized Norrish ? photoinitiators are mainly used in the photocuring system under the mercury lamp light source.With the popularization and application of light emitting diode(LED)light sources,the development of new types of Norrish Type ? photoinitiators suitable for LED light sources is urgently needed in photocuring technology.Therefore,according to the characteristics of Norrish type ?photoreaction of ?-diketone,?-carbonyl methyl ester and oxime ester compounds,this thesis developed some photoactive organic small molecules with D-A structure and intramolecular charge transfer characteristics by introducing the aromatic amine groups which possess rigid conjugated structure,excellent electron donating ability and low oxidation potential.By exploring the photophysical and photochemical reaction characteristics of these organic small molecules under LED light source,the theoretical basis for the development of Norrish ?photoinitiator and the development of a multi-component photoinitiator systems with high efficient will be provided The main work of this paper is as follows:1.Using carbazolyl,naphthalene and triphenylamine groups as chromophores and ?-dicarbonyl groups as initiator groups,D-A type?-diketone compounds ?-DKs and ?-CDKs with absorption properties in the visible region were constructed.In the free radical photopolymerization system under the LED light source,?-DKs and?-CDKs exhibit high-efficiency as Norrish I photoinitiatos.Through studies of phosphorescence spectroscopy and transient absorption spectroscopy of ?-DKs,the excited triplet-induced polymerization with?-DKs and ?-CDKs as photoinitiato was revealed,and the structure-effect relationship of excited state properties such as triplet type,lifetime and transition probability were studied.The results of steady-state photolysis and electron paramagnetic resonance(ESR-ST)experiments confirmed that ?-DKs and ?-CDKs can undergo Norrish I cleavage under light excitation.The photocuring experiments also showed that ?-CDKs with aldehyde groups polarized the C-C bond between carbonyl groups,and as the Norrish I-type photoinitiator,?-CDKs has higher initiation efficiency compared to ?-DKs.2.Using the synthesized ?-DKs and ?-CDKs as the sensitizer of the onium salt photoinitiator(ION),the free radical and cation photopolymerization under LEDs were evaluated.The steady-state photolysis experiment,electrochemical experiment and ESR-ST experiment revealed the charge transfer sensitization mechanism between?-DKs or ?-CDKs and diaryl iodonium salts.The photoinitiation activity of ?-DKs and ?-CDKs in the presence of amine hydrogen donors was examined,the results showed that ?-diketone compounds can also be used as Norrish ? type photoinitiators,and the initiation efficiency is higher than commercial photoinitiator camphorquinone(CQ).The initiation activity of ?-CDKs/benzoyl peroxide(BPO)system in LED photocuring was also examined.The experimental results showed that BPO can promote the cleavage of ?-CDKs and is helpful to the formation of free radicals.3.With arylamine as the electron-donating group and ?-carbonyl methyl ester as the electron-withdrawing group,D-A ?-carbonyl methyl ester compounds(MO)with an absorption wavelength of more than 460 nm were constructed.These compounds also exhibit high-efficiency initiation activity as Norrish type I photoinitiators under LED light sources.Studies of phosphorescence spectroscopy and transient absorption spectroscopy revealed the excited triplet-induced polymerization using MO as photoinitiators,and the structure-activity relationship of the excited state properties including triplet state type,lifetime and transition probability.Steady-state photolysis experiments and ESR-ST experiments showed that ?-dicarbonyl ester compounds can undergo secondary cleavage to generate methyl radicals with higher activity.The photocuring experiments proved that ?-dicarbonyl ester can be used as both type ? photoinitiator and type ? photoinitiator,and can also be used as triplet sensitizer for ION.4.D-?-D-A oxime esters(OXE)with absorption in the visible light region were constructed by using arylamine groups as the electron-donating groups,an oxime ester group as the initiator groups,and a triple bond as the bridging group.The photopolymerization using OXE/amine as photoinitiator were studied.The multi-component initiator systems with oxime esters as sensitizers,including OXE/ION,OXE/EDB,OXE/ION/EDB,OXE/ION/TPP,OXE/ION/NVK system were also evaluated.Experiments of steady-state photolysis,fluorescence quenching,cyclic voltammetry,and ESR-ST revealed that OXE can undergo Norrish type ? reaction under the excitation of a visible light source,and a redox reaction can occur between multi-component systems.The polymerization kinetic curve showed that the initiation efficiency of the three-component initiation system is greater than that of the two-component system and that of the single-component system. |
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