Synthesis Of Photoinitiator Based On N-methylpyrrole Stracture And Its Photoinitiation Performance Research

The photoinitiator is a key component in the photopolymerization system.Under the irradiation of the light source,it generates active species by chemical action to initiate photopolymerization.The traditional photopolymerization light source is a mercury lamp.However,due to the harm of mercury pollution to the environment and biological safety,the use of mercury lamps is restricted.Compared with mercury lamps,light-emitting diodes(LEDs)are more energy-saving and environmentally friendly,and have more advantages.However,due to the limitations of packaging technology and materials,short-wavelength LED light sources are expensive to manufacture and have a short service life.At present,mature LED light sources on the market have longer wavelengths,generally 365nm,385nm,395nm,405nm and above.The absorption wavelength of traditional commercial photoinitiators is usually below 365nm.When using LEDs as light sources,the photoinitiators have difficulty in initiating photopolymerization due to the wavelength mismatch.Therefore,it is of great research significance to develop the photoinitiator with an absorption wavelength that matches the LED light source and has good initiation efficiency.In this study,a kind of long-wavelength benzene ring-free photoinitiator based on N-methylpyrrole structure is designed and synthesized by using aldehyde-ketone condensation reaction.Through the design of molecular structure to adjust the absorption wavelength of the photoinitiator.The photochemical properties of photoinitiators and the initiation efficiency of free radical photopolymerization and cationic photopolymerization applied to LEDs were studied,and their photoinitiation mechanism was discussed.Studies have shown that increasing the hydrogen donor is more conducive to the initiator's initiation efficiency.Since the tertiary amine contained in the initiator structure can self-donate hydrogen,it can also initiate free radical polymerization well without other hydrogen donor.At the same time,it can be used as a photosensitizer in LED cationic photopolymerization to achieve efficient polymerization of long-wavelength cations with low light intensity.The specific research contents and the conclusions:(1)The photoinitiators(BPDO,BCO,MBCO)with different structures were synthesized.Their ultraviolet absorption properties were studied by ultraviolet spectrophotometer and front-line molecular orbital theory,and their kinetic properties of photopolymerization under different conditions were studied by real-time infrared spectroscopy,including free radical photopolymerization and cationic photopolymerization.The photoinitiation mechanism of photoinitiators was studied through steady-state photodegradation,fluorescence spectroscopy,and cyclic voltammetry.The results show that the photoinitiators with three different ketone structures have a D-?-A-?-D conjugated structure composed of N-methylpyrrole,carbon-carbon double bond and carbonyl group.They absorb in the range of 325-500nm and have a high molar extinction coefficient.Compating the efficiency of three photo initiators to initiate acrylate photopolymerization and PI/Iod photoinitiator system to initiate epoxy monomer photopolymerization under LED light,BPDO,BCO,MBCO can initiate HDDA photopolymerization alone.BPDO/Iod initiated EPOX photopolymerization has a very high efficiency.During the steady-state photodegradation process,the absorbance of the maximum absorption wavelength of the three structures continues to decrease after exposure to light,and the solution is accompanied by a photobleaching effect.Fluorescence quenching experiments and cyclic voltammetry tests showed that the electron transfer reaction between BPDO and Iod produced effective cation free radicals(2)Synthesis of the photoinitiator(BMO).Its UV absorption properties were studied by UV spectrophotometer and front-line molecular orbital theory,and photopolymerization kinetic properties were studied by real-time infrared spectroscopy,including free radical photopolymerization,cationic photopolymerization and hybrid photopolymerization.The photoinitiation mechanism of BMO and BMO/Iod was studied by steady-state photodegradation,fluorescence spectroscopy,cyclic voltammetry and electron paramagnetic resonance.The film formation performance at different times under low light intensity and the actual effect of 3D printing were studied.The results show that:BMO has a larger conjugated structure with an absorption range between 325-450nm and a large molar extinction coefficient.Compared with BPDO in(1),the degree of conjugation is reduced.Under the LED 405nm light and oxygen-free conditions,it has a good curing effect on the free radical photopolymerization of acrylates.For example,TPGDA can achieve a photopolymerization conversion rate of more than 90%for 600s.In addition,the BMO/Iod photoinitiator systems have an excellent curing effect on the cationic photopolymerization of epoxy monomers.When irradiated with LEDs at 405nm for 300s,the final conversion rate reaches more than 60%.In the study of steady-state photodegradation,the absorbance of the maximum absorption wavelength of BMO drops rapidly after being exposed to light,and it has an excellent photobleaching effect.Fluorescence quenching experiments,cyclic voltammetry,and EPR indicate that the electron transfer reaction between BMO and Iod generates free radical cations to initiate epoxy polymerization.The photopolymerization of the hybrid system in the air initiated by the BMO/Iod system shows that the photopolymerization of the acrylate ester in the hybrid system is less affected by the oxygen polymerization inhibition,and the epoxy photopolymerization in the system is more effective.The BMO/Iod formulation has been applied to LED cationic 3D printing technology and achieved good results.EPOX/MOX-104 cationic monomer reacted at 15mW/cm2 LED for 60s to obtain 0.236mm film.Finally,the DLP printer was used to realize cationic photopolymerization 3D printing.