Study On Properties Of Epoxy Photoinitiator System Of Aromatic Iodonium Salts

Compared with radical curing,epoxy ring-opening cationic photocuring is not particularly affected by oxygen in the air.So it's particularly suitable for curing thick films and colored systems.Diaryliodonium salt,which is one of the initiators with the best initiating effect in the cationic curing system,has the advantages of highly initiation efficient activity and it's easy sensitized.In response to the long-wavelength absorption of diaryl iodonium salts,a great deal of work has been done,mainly focusing on the selection of sensitizers and the increase in the degree of conjugation of conjugated aromatic hydrocarbons with iodonium salts.However,there are few studies on the effect of the structure of substituents on iodonium salts on the sensitization activity of iodonium salts.In this paper,eight kinds of diaryliodonium salts with different substituents were experimentally synthesized.The photoinitiating activity of a photoinitiator system composed of a sensitizer in a cationic photopolymerization system was examined to reveal the role of different substituents on the iodonium salt aromatics.Using isopropyl ketone IX as sensitizer and 395 nm LED lamp as the radiation source,the effect of the photoinitiation system composed of IX and different substituent iodonium salts on the ring opening polymerization rate of epoxy was investigated by real-time near infrared spectroscopy.It was found that there was no initiator system with an alkyl-substituted diphenyliodonium salt hexafluorophosphate and IX,which had the highest initiating activity.With the increase of the spatial structure of substituents on the aryl ring of iodonium salt,the initiating system activity with IX composition was reduced.In addition,the initiating system consisting of an iodonium salt and IX with an electron-withdrawing group is superior to the initiating system of the iodonium salt and IX of the donor group.Based on the Rehm-Weller equation,photoelectron transfer effects between iodonium salts and IX of different substituents were investigated.It was found that the photoelectron transfer activation energies between the iodonium salts of different substituents and IX were both negative,and the change law of activation energy is consistent with that of the above sensitization system.At the same time,it is consistent with the reduction potential of iodonium salts of different substituents.The orbital energy levels of the HOMO and LUMO of the different substituted iodonium salts were predicted by DFT theory,and it was found that the change law is consistent with the sensitized activity.With xylene iodine hexafluoroantimonate and IX as the initiation system,The effect of the different proportions of the composition of the epoxy polymer ERL4221 and EHO on the photopolymerization rate of the system was investigated by optical pyrometry(OP method)under a 395 nm LED light source.The degree of cross-linking of photopolymerization systems with different proportions was studied by gel-rate method.The characteristic peaks before and after curing of the system were compared by infrared spectroscopy to further prove that the two resin monomers have undergone ring-opening polymerization and changed from a liquid state to a solid state.