Preparation And Properties Of A Thiophene Long-wavelength Photoinitiator

Photopolymerization technology is an environmentally friendly and efficient curing technology with a wide range of applications.Photopolymerization is a process in which a photoinitiator absorbs energy from a light source to generate an active species to initiate polymerization of a monomer or resin.The traditional light source is a mercury lamp.The ozone produced by long-term use of mercury lamps will cause environmental pollution,and the leakage of mercury will cause "Minamata disease."Therefore,the UN Environment Council adopted the Minamata Convention to restrict the use of mercury-containing products.Since the use of mercury lamps will also be restricted,new environmentally friendly LED lamps will replace them.LED lamps are subject to packaging technology,and the manufacturing technology of shorter wavelength LED lamps is not mature enough.At present,the emission wavelengths of common LED lamps on the market are 365nm,385nm,395nm and 405nm.Traditional photoinitiators are mainly used in conjunction with traditional mercury lamps,with shorter absorption wavelengths,and low or no absorption of the emission wavelength of common LED lamps.Therefore,long-wavelength photoinitiators that can well match the emission wavelength of LED lamp sources are the inevitable trend of photoinitiator research.This subject has designed a long-wavelength photoinitiator and synthesized it in one step.The molecular structure was characterized by nuclear magnetic,the ultraviolet spectrophotometer characterized the ultraviolet absorption spectrum and ultraviolet degradation performance of the photoinitiator,and analyzed its photochemical and photophysical changes;the photopolymerization kinetics of the photoinitiator was tested by real-time infrared,and Study its photo-induced performance.Finally,the molecular structure was optimized,and the optimized structure was tested and characterized to study its photopolymerization kinetics,and finally a longer-wavelength photoinitiator with better performance was obtained.The conclusion of the study is as follows:1.Designed and prepared three long-wavelength photoinitiators,namely 1,5-bis(thiophen-2-yl)penta-1,4-dien-3-one(BTO)and 2,6-bis(Thiphen-2-ylmethylene)cyclohexanone(BTCO)and 4,4-dimethyl-2,6-bis(thiophen-2-ylmethylene)cyclohexanone(DBTCO),the synthesis raw materials were simple and easy to obtain,the preparation conditions were mild,and it could be prepared through one-step reaction,and the yield was high,and the product was easy to purify.These three photoinitiators have strong absorption in the absorption wavelength range from 300nm to 430nm,and can effectively initiated the photopolymerization of acrylate monomers under the irradiation of 365nm LED lamps,and the optimal initiation concentration was extremely low at 0.01wt%.This is mainly due to the high molar extinction coefficient of these three photoinitiators.In addition,according to the ultraviolet degradation diagram,it can be seen that they have photobleaching properties.The initiation effect of these three photoinitiators in PEGDA monomers containing hydrogen donors was significantly better than that in HDDA monomers without hydrogen donors,because these three photoinitiators have a complexation with PEGDA monomers.The photo-induced cis-trans isomerization phenomenon was suppressed,and the ether structure in the PEGDA monomer has the function of hydrogen supply.2.By illuminating BTO's acetonitrile solution and collecting its light products,liquid-mass spectrometry analysis of the light products found that photo-induced[2+2]addition reaction occurs between BTO molecules.When BTO was exposed to light,the intermolecular[2+2]addition reaction consumes energy and reduces its photoinitiation efficiency,which was one of the reasons for the low photoinitiation efficiency of BTO;3.Based on the research of BTO series photoinitiators,BTO has a long absorption wavelength to make it color.Through structural design,we reduced the number of double bonds to reduce cis-trans isomerization,and reduce the degree of conjugation to shorten the absorption wavelength.Three photoinitiators were designed and prepared,namely 1,3-bis(thiophen-2-yl)prop-2-en-1-one(DTO)and 3-(furan-2-yl)-1-(Thiophen-2-yl)prop-2-en-1-one(FTO)and 1,3-bis(furan-2-yl)prop-2-en-1-one(DFO),the three photoinitiators were has good absorption in the wavelength range of 300-400nm,and could still be well matched with 365nm LED light source to initiate photopolymerization.These three types of photoinitiators could effectively initiate the photopolymerization of acrylate monomers.They were lighter in color and the initiation effect was significantly better than BTO series photoinitiators,indicating that the structure optimization was reasonable and feasible.