Novel Organozirconiums:the Preparation And The Photopolymerization Kinetics Of Overcoming Oxygen Inhibition In The UV-curing System

UV-curing technology has been widely concerned in recent years due to its advantages of high efficiency,energy saving and low pollution.It is gradually replacing the thermal curing process in the material production and processing industry.But the process of UV-curing could be suffered from oxygen inhibition,which leads to tackness of the product surface.And photolysis products in the UV-cured system may undergo migration,discoloration and other undesirable process,which severely limits the popularization of UV-curing technique in industial applications,such as food packaging materials.A large number of studies have focused on the methods of overcoming the oxygen inhibition during the photopolymerization and the design of macromolecular photoinitiators to solve these two defects.Organometallic compounds are used as additives to overcome the oxygen inhibition because they are sensitive to peroxide radicals during the photopolymerization.In this paper,a new type of organozirconium compounds with multi-functions was prepared by the ligand substitution of organic zirconium compounds.The synthesis method has the advantages of simple operation and catalyst-free,and the products maintain a certain activity to peroxides.The properties of organozirconiums are studied and as well as the UV-curing formulations.The specific research contents are as follows:1.A commercial photoinitiator,2-hydroxy-2-methylpropiophenone(PI-1173),was employed to synthesize a novel multifunctional photoinitiator(MPI)via ligand substitution of zirconium propoxide in the absence of any catalyst.With different feed ratios of the reactant,trifunctional and tetrafunctional zirconium-based photoinitiators were prepared.The photoinitiation properties of the MPIs were evaluated by real-time FTIR of the UV-curing formulations,which shows that the photoinitiation ability of MPIs were comparable to PI-1173.Three different levels of final conversion were achieved with varied concentrations of MPIs.The residual-free PIs in UV-cured samples were also measured by extraction of chloromethane.The results show that Zr-tri1173 and Zr-tetral 173 had slightly lower amounts of migrating products than PI-1173 in UV-cured samples with lower conversion,and Zr-tetral 173 was slightly lower than Zr-tri1173.In the samples with high conversion,the ones with Zr-tri1173 and Zr-tetra1173 have similar amount of migrating products,but it is greatly reduced compared with PI-1173.The multifunctional structures of MPIs are more immobilized in the cross-linked networks than the parent molecule.2.Two hydroxyl derivatives of benzophenone and anthraquinone were chosen as the ligands of zirconium complexes in the substitution of zirconium propoxide to obtain zirconium-based multifunctional photoinitiators(MPIs),Zr-OBP and Zr-OAQ.The MPIs were characterized in terms of molecular structures,UV-vis absorption properties and photoinitiation reactive ability.The absorption bands of the MPIs are similar to their low-molecular-weight counterpart with higher absorbance.These photoinitiators were used for the UV-curing of a formulation with bisphenol A diacrylate(SR349)and hexanedioldiacrylate(HDDA).The kinetics of photopolymerization of the formulations was monitored by real-time FTIR spectroscopy,under the irradiation of a mercury-xenon lamp.The results show that under the same conditions,multifunctional photoinitiators can achieve a higher final conversion rate of the formulation.Organozirconium complexes are known to tap the potential of overcoming the oxygen inhibition,thus the depth conversion profiles of the UV-cured films were followed by confocal Raman microscopy.Furthermore,the migration of residual photoinitiator was investigated via solvent extraction from the UV-cured films,the solution of which being measured by UV-vis spectroscopy.3.Organozirconiums had been studied as the peroxyl radical scavenger in UV-curing systems,which had varied performance in overcoming the oxygen inhibition.Herein we modified the complex of zirconium with organic fluorides in order to increase its efficiency of peroxyl radical scavenging.A formulation consists of two conventional monomers(Ebercyl 270 and TPGDA)and an oxygen-sensitive photoinitiator TPO was employed in this study.With different content added in the formulation,the UV-cured coatings had different depth conversion profiles,which were measured by confocal Raman microscopy.Moreover,the standing time for the enrichment of fluorinated organozirconium products to the surface of the coatings and two irradiation sources(Hg-Xe lamp and UV-LED lamp)were adopted to emphasize their properties against the oxygen inhibition.Finally,by adjusting the irradiation intensity,it is shown that fluorinated organozirconiums can lead to tack-free coatings,while the UV-cured films from neat formulation remain tacky.