Design,Synthesis And Properties Research Of Benzoyl Methylformate Derivatives As Led Photoinitiators

There is a trend of light emitting diodes(LED)-induced photopolymerization technology gradually replacing traditional ultraviolet light(UV)photopolymerization technology in field of photopolymerization because LED sources have advantages of long service life,low energy consumption,safety,environmental protection and rapid emission compared with conventional mercury lamps.Traditional photoinitiators(PIs)cannot be used in LED photopolymerization systems due to that the absorption wavelengths of PIs are difficult to match the emission wavelengths of LED sources.Therefore,the development of PIs matching the LED sources has become a research hotspot in recent years.However,the previously-reported PIs for LED photopolymerization systems still have some drawbacks.For instance,large-conjugated structures(chromophores)of PIs lead to a poor solubility of PIs in monomers and photocured product to be color,and block deeper light penetration,which seriously limits their application in colorless and thick film curing systems.In addition,the water-based LED photopolymerization systems have also become one of the frontiers of photopolymerization technology in recent years due to their advantages such as safety,environmental protection and low toxicity.Correspondingly,the development of water-soluble PIs for water-based LED photopolymerization has also become a research focus.At present,most of the previously-reported water-soluble PIs are organic salts,which can introduce metal or halide ions into polymeric materials,thereby harming to properties of materials.However,the non-ionic water-soluble PIs containing amphipathic organic groups can overcome these disadvantages and have wider applications.The colorless methyl benzoylformate(MBF)that has been widely used in field of UV photopolymerization,has a weak absorption around 400 nm,which is beneficial for the light penetration into deep layers and may endow it with a potential application in field of LED photopolymerization.Based on the backgrounds,this project aims to design and synthesize a series of MBF derivatives that can be used in deep layers and water-based LED photopolymerization systems.We have explored their photophysical and photochemical properties,the capability of photoinitiation and the potential application in the field of deep layers as well as water-based LED photopolymerization,and clarified their photolysis and photoinitiation mechanisms to obtain the intrinsic relationship between structures and properties of PIs and provide theoretical and technical support for the development of PIs used for deep layers and water-based LED photopolymerization systems.The research has important theoretical significance and application value.The main research contents and conclusions are as follows:(1)Ten MBF derivative PIs(MBFs)for deep layers LED-induced photopolymerization were designed and synthesized.Their light absorption properties,photolysis mechanism,capability to initiate photopolymerization were studied.The results show that the maximum absorption wavelengths of MBFs were mostly concentrated around 270 nm,and the molar extinction coefficients in the emission wavelength range of LED were very weak.MBFs underwent two-step cleavage to generate benzoyl radicals and methyl radicals to initiate photopolymerization reaction under the irradiation of LED source.The cleavage exothermy(?H)of MBFs were calculated by computer,and the photoinitiating capabilities of MBFs were accurately predicted based on the value of ?H.The results of photopolymerization kinetics show that MBFs can be used in field of LED photopolymerization,and the introduction of strong electron-donating substituents on the benzene ring of MBFs can reduce their photoinitiation capability,while the introduction of strong electron-withdrawing substituents can improve the photoinitiation capability.The capabilities of as-synthesized F-MBF,TF-MBF and MO-MBF to initiate deep layers photocuring(photopolymerization depth reached 6.6 cm)were much better than that of commercial phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide(BAPO,photopolymerization depth was 1.0 cm).The three photoinitiators have a great potential application in LED-induced deep layers photocuring.(2)Five amphiphilic PIs(BFAs and TGBFs)for LED-induced photopolymerization based on the structures of MBF,TF-MBF and MO-MBF were designed and synthesized.Their light absorption properties,photolysis mechanism,the solubilities in water and capabilities to initiate photopolymerization were studied.The results show that the maximum absorption wavelengths of five amphiphilic PIs were mainly concentrated around 250 nm,and their molar extinction coefficients in the emission wavelength range of LED were very weak.BFA,TF-BFA and CC-BFA with carboxyl groups generated substituted-benzoyl radicals and carbon dioxide under the irradiation of LED source,and substituted-benzoyl.radicals can initiate photopolymerization of monomers.TGBF and TF-TGBF with long ether chains underwent an intramolecular or intermolecular hydrogen abstraction reaction under the irradiation of LED source to generate alkyl radicals to initiate photopolymerization reaction.Five amphiphilic PIs have good water-solubility that reached up to 10 wt%.BFAs and TGBFs can initiate the photopolymerization reactions of oil-based and water-based monomers.TGBFs with long ether chains possessed more excellent capabilities of the photoinitiation than BFAs when initiating photopolymerization reactions of oil-based monomers.The final double bond conversions all were about 80%,when five amphiphilic PIs initiated the photopolymerization of the water-based polyethylene glycol(400)diacrylate(PEG(400)DA).BFA,TGBF,TF-BFA and TF-TGBF have excellent capabilities to initiate water-based deep layers photocuring(the photopolymerization depth were all more than 6.0 cm)and a tremendous potential application in water-based LED-induced deep layers photocuring.