| Photopolymerization technology has great potential applications in the areas of dental,3D and 4D printing,adhesives,laser writing,food and medical treatment for the advantages of green and environmental protection,high efficiency and energy saving,economy and controllability,However,due to the restrictions on the use of mercury in international environmental protection law,the traditional UV mercury lamp light source used in photopolymerization technology will be replaced by energy-saving and environment-friendly LED light source,resulting in the problem of wavelength mismatch between traditional commercial UV photoinitiators and LED light source.In addition,the current photoinitiators are easy to migrate from curing films,leading to yellowing,odor and toxicity,which greatly limited the application in food packaging and other safety fields.To overcome the above defects,polymerizable photoinitiators,phenothiazine based photoinitiators and double chalcone photoinitiators were successfully prepared.The photophysical and chemical properties,initiation mechanism and migration stability were explored,providing a basis for the development and application of new photoinitiators.（1）Aiming at the defects of poor migration performance of Irgacure 184,four new polymerizable photoinitiators PI1-PI4 were designed and synthesized by combining Irgacure184 with polymerizable double bond groups,the structures were characterized by infrared spectroscopy and nuclear magnetic resonance.The photophysical properties shown that PI1-PI4 had similar UV absorption spectrum with Irgacure 184,while the molar absorption coefficient was increased from 15000 M-1cm-1（Irgacure 184）to 29200 M-1cm-1（PI4）.PI1-PI4 showed high photoinitiation and short curing time（15 s）when applied to the photopolymerization system.Meanwhile,as self-initiating resin,PI1-PI4 have good compatibility with monomer,the hardness of the photocured coatings were higher than Irgacure 184,and PI1-PI4 has good thermal stability.Besides,PI1-PI4 shown low migration performance for the existence of C=C bond in molecular structure,which was easier to be crosslinked and fixed in the polymer network structure.（2）In view of the disadvantages of mercury pollution and harm to human body of UV light source,two phenothiazine-based photoinitiators（E）-4-（10-methyl-10H-phenothiazin-3-yl）but-3-en-2-one（PBO）and（1E,4E）-1,5-bis（10-methyl-10H-phenothiazin-3-yl）penta-1,4-dien-3-one（BMPPO）for LED photopolymerization were designed and synthesized,the maximum absorption wavelengths were 400 nm and 442 nm respectively.Three component initiator system（BMPPO/IOD/EDAB）can efficiently initiate free radical polymerization with the double bond conversion reach more than 90%.The drying time of the films was short（5-10 s）irradiated by light sources at 365 nm,442 nm and sunlight.Besides,the maximum absorption wavelength intensity of BMPPO in the photolysis process decreased significantly with the increase of irradiation time.Moreover,BMPPO shown certain photobleaching ability,which was conducive to the deep curing of the coating.Cytotoxicity experiments shown that PBO and BMPPO have good biocompatibility,exhibiting high potential application in food packaging and biological medicine fields.（3）Using phenothiazine as electron donor group,four new D-A visible light photoinitiators（10-methyl-phenothiazin-2-yl）（phenyl）methanone（MPO）,（10-methyl-phenothiazine-2,8-diyl）bis（phenylmethanone）（MPBO）,（E）-1-（10-methyl-phenothiazin-2-yl）-3-phenylprop-2-en-1-one（MPPO）and（2E,2’E）-1,1’-（10-methyl-phenothiazine-2,8-diyl）bis（3-phenylprop-2-en-1-one）（MPBPO）were synthesized by one-step method with good solubility in different monomers.The effect of carbonyl group and C=C bo nd on the photophysical properties was studied,the results shown that the absorption wavelength redshifted from 385 nm（MPO）to 430 nm（MPBPO）with the increase of carbonyl group and C=C bond.The charge transfer between the two-component photoinitiator system（Iod as coinitiator）can significantly improve the photopolymerization efficiency,the conversion rate of C=C bond can reach to 80%,and the drying time of coatings was within 5-20 s,which can be used in the polymerization system irradiated by UV-LED light source.Meanwhile,MPO,MPBO,MPPO and MPBPO shown low migration and low cytotoxicity properties.（4）In consideration of the shortcomings of complex synthetic route and high price of photoinitiator for LED photopolymerization,six new double chalcone compounds（1E,4E）-1,5-diphenylpenta-1,4-dien-3-one（DKE-1）,（1E,4E）-1,5-di（naphthalen-2-yl）penta-1,4-dien-3-one（DKE-2）,（1E,4E）-1,5-di（anthracen-9-yl）penta-1,4-dien-3-one（DKE-3）,（1E,4E）-1,5-di（pyren-1-yl）penta-1,4-dien-3-one（DKE-4）,（1E,3E,6E,8E）-1,9-diphenylnona-1,3,6,8-tetraen-5-one（DKE-5）,（3E,6E）-1,9-diphenylnona-3,6-dien-1,8-diyn-5-one（DKE-6）were prepared and synthesized by Claisen-Schmidt reaction.The influence of different thick-ring structures and the introduction of unsaturated groups on the light absorption performance of DKEs was studied.For DKE1-DKE4,with the increase of the number of benzene rings in the molecular structure,the absorption wavelength gradually red-shifted to the visible region,and the maximum absorption wavelength of DKE-4 was 442 nm.Meanwhile,with the introduction of C=C bonds and C≡C bonds for DKE-5 and DKE-6,the absorption wavelengths also redshift and the maximum absorption wavelength of DKE-6 was 395 nm.However,with the increase of polycyclic aromatic hydrocarbons in the structure of photoinitiators,the solubility of photoinitiators in organic solvents and monomers gradually decreases,the synthesis of DKE-5and DKE-6 can effectively solve the problem of difficult dissolution.DKEs photoinitiator can efficiently and quickly photopolymerization under the synergistic action of co-initiators with the double bond conversion more than 80%.DKEs can be used for deep curing of coatings for the properties of certain photobleaching.In addition,DKEs shown low migration with the increase of relative molecular weight and the extraction mobility of DKE-4 was only 0.7%. |
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