Synthesis And Application Of Acylphosphine Oxide Low Migration Photoinitiators For UV-LED Photopolymerization

The photopolymerization technology has the characteristics of high efficiency,economy,energy saving,environmental friendliness and wide adaptability,and it has been widely used in coatings,adhesives,inks,photosensitive printing plates,photoresist,dental materials and other fields.In recent years,the Minamata Convention on Mercury and relevant international environmental laws and regulations have been proposed to limit the use of mercury lamp.LightEmitting Diode(LED)possesses the distinct advantages over traditional mercury lamp,and therefore,it has been widely concerned and applied in photopolymerization.However,there is a mismatching between the absorption wavelengths of the existing photoinitiators and the emission spectrum of the UV-LED source.In addition,the application of traditional photoinitiators in food packaging coatings and medical materials is limited because the residual photoinitiators can migrate to the surface of the polymer after photocuring.In this thesis,based on the characteristics of photoreaction of cleavage acylphosphine oxide,different series of low migration acylphosphine oxide photoinitiators matching the emission spectrum of UV-LED light source have been designed and synthesized by introducing the structures of polymerizable amino group,polymerizable ether oxide group,macromolecule ether oxide group and diacylphosphine oxide group.Their photophysics and photochemical properties under UV-LED light,solubility in the monomer and mobility in cured polymer were studied,which provided theoretical basis and research approach for the design and synthesis of low mobility acylphosphine oxide photoinitiators.The work of this paper is as follows:(1)To solve the problem of high mobility of diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide(TPO),the dominant photoinitiator in the market,and to further optimize the spectral matching between the photoinitiator and UV-LED light source,three 4-diallylamine acylphosphine oxide(DABPOs)derivatives were designed and synthesized by introducing strong electron donor and polymerizable diallyl amino into the benzoyl group.DABPOs has strong absorption at 350-420 nm,with a maximum absorption range reaching to 470 nm,which overlaps the UV-LED emission spectrum.The steady-state photolysis and electron paramagnetic resonance resonance(EPR-ST)experiments showed that DABPOs underwent cracking reaction and generated phosphonyl radicals.Under the irradiation of LED@420nm,the double bond conversion of DABPOs initiated photopolymerization system was higher than that of TPO.The monomer solubility and migration resistance of DABPOs are significantly better than that of TPO.When the addition amount was 2 wt%,the mobility of DABPOs(0.11%,0.23%,0.46%)was lower than that of commercial TPO(1.15%).In addition,the steady-state photolysis and photoinitiation efficiency of DABPOs as hydrogen donor in DABPOs/DETX(2,4-diethylthioxanthrone anthraquinone)system under UV-LED light source were investigated.The results showed that DABPOs could promote DETX photodegradation as hydrogen donor with photoinitiation activity.(2)In order to solve the problems of high molar extinction coefficient of DABPOs and low photoinitiated efficiency at LED@385nm,benzoyl groups were modified with weak electron-donating polymerized allyl group instead of diallyl amino group,and two 4-allylphosphine oxide derivatives(APO,DAPO)containing C=C were obtained.The UV-vis absorption spectra show that the molar extinction coefficients of APO and DAPO are both lower than that of DABPOs.The results of steady-state photolysis and EPR-ST showed that DAPO and APO decomposed into phosphonyl radicals and the photoinitiation efficiency of DAPO was higher than that of commercial TPO under LED light source.On the other hand,when the addition amount was 2 wt%,the mobilities of APO and DAPO are lower than that of commercial TPO.Therefore,APO and DAPO can be used as UV-LED,low migration and cleavable photoinitiators.(3)In order to further reduce the mobility of DAPO,eight 4-oxy-acylphosphine oxide derivatives(DAPOs)with different molecular weights(404.4-516.6 g/mol),which are all higher than that of TPO(348.4 g/mol),were synthesized by introducing oxygen substituents with different chain length into para-position of benzoyl.The UV-vis absorption spectra show that DAPOs’ absorption spectra match UV-LED emission spectra.When the addition amount was 2 wt%,the mobility of DAPOs in the photocured coating was much lower than that of other photoinitiators under UV-LED irradiation,the mobility of DAPO-4 is as low as 0.03%,which indicates that increasing the molecular weight of photoinitiator was beneficial to reduce the mobility of DAPOs.(4)The large molecular weight of low migration photoinitiators results into relatively low photoinitiating efficiency per unit mass.In order to balance this contradiction,three bisacylphosphine oxide macromolecular photoinitiators(BTPOs)were synthesized using ethoxyl as the bridging group to link two acyl phosphine oxide groups,and thier molecular weights(690.71-866.92 g/mol)are more than twice that of TPO-L(316.34 g/mol).The photocuring experimental results showed that the photoinitiation efficiency of BTPOs was comparable to that of 2,4,6-trimethylbenzoylphenyl-phosphonate(TPO-L).When the addition amount was 2 wt%,the mobility of BTPOs in the photocuring film was lower than the detection limit of 0.02‰,which was much lower than that of TPO-L(0.98%).The results of steady-state photodegradation and EPR-ST showed that BTPOs decomposed to produce phosphine radicals under UV-LED excitation.Therefore,BTPOs can be used as cracking photoinitiator suitable for UV-LED light source with high photoinitiation efficiency and low migration.(5)In order to evaluate the application performance of the low migration acylphosphine oxide photoinitiators synthesized in this doctoral dissertation,the photoinitiators(DAPO,DAPO-4,BTPO-1,BTPO-2,BTPO-3)and commercial photoinitiators(TPO,TPO-L)were adopted to prepare transparent varnish to compare the basic properties of the coating and the photoinitiator mobility after photocuring.The results show that photoinitiators prepared in this work have excellent solubility in the formulation,the wet and the dry film are both transparent and colorless,the surface is dry within 5 seconds,the pencil hardness is 2H-3H,the photoinitiator can be cured deeply,and the mobility is lower than that of commodity(TPO,TPO-L).Therefore,the photoinitiator can meet the industrial requirements for UV-LED photoinitiators with low mobility.