Acylphosphine Oxide Photoinitiator Research Articles

Acylphosphine oxide photoinitiators containing Si with sulfhydryl bridge linkages

Two novel small-molecule acylphosphine oxide photoinitiators incorporating organosilicon, named TPO-Si and TPO-L-Si, have been synthesized using the commercial photoinitiators 2,4,6-trimethylbenzoyldiphenylphosphine oxide (TPO) and 2,4-trimethylbenzoylphenylphosphonate (TPO-L). TPO-Si and TPO-L-Si optical characteristics were studied using steady-state photolysis, electron paramagnetic resonance measurements, and UV–visible absorption spectroscopy. Although the photopolymerization efficiency of TPO-Si and TPO-L-Si is slightly lower than that of TPO and TPO-L, they exhibit higher compatibility with methyl methacrylate-based polydimethylsiloxane (MTQ-570), as indicated by photopolymerization experiments. Furthermore, TPO-Si and TPO-L-Si exhibit greater thermal and migratory stability, and the cured films produced by TPO-Si and TPO-L-Si are more hydrophobic.

New acyl phosphine oxides as high-performance and low migration type I photoinitiators of radical polymerization

Two low migration acylphosphine oxide photoinitiators (APO and DAPO) containing unsaturated CC double bonds have been designed and synthesized for free radical polymerization. The properties and performances of APO and DAPO in the free radical polymerization of trimethylolpropane triacrylate (TMPTA) were evaluated and compared with the commercial photoinitiator 2,4,6-trimethyl(phenyl) diphenyl oxide (TPO). The results show that DAPO exhibited the best double bond conversion (DC) of TMPTA in the photoinitiators tested under the same reaction conditions. The migration ratio of APO and DAPO was 2/3 and 1/3 of that of TPO respectively indicating lower migration than the conventional photoinitiator, and the solubility of DAPO in monomers was close to that of TPO, which provided the possibility for the industrial application of DAPO.

The Photoinitiators Used in Resin Based Dental Composite-A Review and Future Perspectives.

The presented paper concerns current knowledge of commercial and alternative photoinitiator systems used in dentistry. It discusses alternative and commercial photoinitiators and focuses on mechanisms of polymerization process, in vitro measurement methods and factors influencing the degree of conversion and hardness of dental resins. PubMed, Academia.edu, Google Scholar, Elsevier, ResearchGate and Mendeley, analysis from 1985 to 2020 were searched electronically with appropriate keywords. Over 60 articles were chosen based on relevance to this review. Dental light-cured composites are the most common filling used in dentistry, but every photoinitiator system requires proper light-curing system with suitable spectrum of light. Alternation of photoinitiator might cause changing the values of biomechanical properties such as: degree of conversion, hardness, biocompatibility. This review contains comparison of biomechanical properties of dental composites including different photosensitizers among other: camphorquinone, phenanthrenequinone, benzophenone and 1-phenyl-1,2 propanedione, trimethylbenzoyl-diphenylphosphine oxide, benzoyl peroxide. The major aim of this article was to point out alternative photoinitiators which would compensate the disadvantages of camphorquinone such as: yellow staining or poor biocompatibility and also would have mechanical properties as satisfactory as camphorquinone. Research showed there is not an adequate photoinitiator which can be as sufficient as camphorquinone (CQ), but alternative photosensitizers like: benzoyl germanium or novel acylphosphine oxide photoinitiators used synergistically with CQ are able to improve aesthetic properties and degree of conversion of dental resin.

Naphthyl-based acylphosphine oxide photoinitiators with high effiency and low migration

A series of new naphthyl-based acylphosphine oxides (N1–N3) have been designed and synthesized. The obtained compounds could be used in the photo-initiated free radical polymerization (FRP). The performances of N1–N3 in the FRP of trimethylolpropane triacrylate (TMPTA) and their UV–vis spectra were evaluated and compared with 2,4,6-trimethyl(phenyl)diphenyl oxide (TPO, a commercial photoinitiator). Results showed that N1–N3 possessed higher molar absorption coefficients and wider absorption wavelength than TPO. Under the same reaction conditions, N3 exhibited the best double bond conversion (DC) of TMPTA in the tested photoinitiators. Moreover, the calculated migration of N1–N3 of the solidified samples was 1/7, 1/3 and 1/23 of TPO, indicating the lower migration properties. Possible reasons of the performance of N1∼N3 were proposed.

Evaluation of acylphosphine oxide polymerization initiators using differential scanning calorimetry

This study examines the polymerization of dental monomers catalyzed by synthesized acylphosphine oxides in a differential scanning calorimetry (DSC) cell. This research focuses on establishing a relationship between radicals generated by the acylphosphine oxide photoinitiators and the kinetic reaction rates of methyl methacrylate (MMA) and acrylamide (ACM), a model monomer. The thermal stability of mono- and di-acylphosphine oxides was examined by DSC. Endothermic melting and exothermic polymerization reactions initiated with the two initiators were recorded. The acrylamide model system laid the ground work for the critical evaluation of the synthesized new initiators of mono (2,4,6-trimethylbenzoyl) diphenylphosphine oxide, and bis(2,4,6-trimethylbenzoyl) phenylphosphine oxide. The bis(acyl) phosphine oxide photoinitiator was more reactive than the mono-(acyl) phosphine oxide with methyl methacrylates under laboratory conditions. In exothermic reactions, temperatures rose higher and more rapidly for bis(acyl) phosphine oxide initiated reactions than mono-(acyl) phosphine oxide initiated reactions.

Photoinitiated polymerization of PEG-diacrylate with lithium phenyl-2,4,6-trimethylbenzoylphosphinate: polymerization rate and cytocompatibility

Due to mild reaction conditions and temporal and spatial control over material formation, photopolymerization has become a valuable technique for the encapsulation of living cells in three dimensional, hydrated, biomimetic materials. For such applications, 2-hydroxy-1-[4-(2-hydroxyethoxy) phenyl]-2-methyl-1-propanone (I2959) is the most commonly used photoinitiator (by virtue of its moderate water solubility), yet this initiator has an absorption spectrum that is poorly matched with wavelengths of light generally regarded as benign to living cells, limiting the rate at which it may initiate polymerization in their presence. In contrast, acylphosphine oxide photoinitiators, generally exhibit absorption spectra at wavelengths suitable for cell encapsulation, yet commercially available initiators of this class have low water solubility. Here, a water soluble lithium acylphosphinate salt is evaluated for its ability to polymerize diacrylated poly(ethylene glycol) (PEGDA) monomers rapidly into hydrogels, while maintaining high viability during direct encapsulation of cells. Through rheometric measurements, the time to reach gelation of a PEGDA solution with the phosphinate initiator is one tenth the time for that using I2959 at similar concentrations, when exposed to 365 nm light. Further, polymerization with the phosphinate initiator at 405 nm visible light exposure is achieved with low initiator concentrations and light intensities, precluded in polymerizations initiated with I2959 by its absorbance profile. When examined 24 h after encapsulation, survival rates of human neonatal fibroblasts encapsulated in hydrogels polymerized with the phosphinate initiator exceed 95%, demonstrating the cytocompatibility of this initiating system.

2-Mercaptothioxanthone as Sensitizer and Coinitiator for Acylphosphine Oxide Photoinitiators for Free Radical Polymerization

The initiation efficiencies of photoinitiators for free radical polymerization, 2,4,6-trimethylben- zoyldiphenylphosphine oxide (TMDPO) and bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide (BAPO), are enhanced by addition of mercaptothioxanthone (TX-SH) to the initiator formulation. The additive TX-SH combines the benefits of a triplet sensitizer (enhanced light absorption) and thiol functionality (reduced oxygen inhibition). On the basis of polymerization studies, laser flash photolysis, fluorescence, and phosporescence, the following mechanism is proposed: most of the light is absorbed by TX-SH to generate 3 (TX-SH)*, which transfers its energy to TMDPO and BAPO followed by R-cleavage to produce the initiating radicals. In addition, excellent polymerization yields were observed in air-saturated solutions when TX-SH was added. With the addition of TX-SH to initiation formulations, the inhibition due to oxygen is reduced, probably by the generation of reactive thiyl radicals by hydrogen abstraction of inactive peroxyl radicals from the thiol functionality.

Redox and photoinitiated crosslinking polymerization: I. Dual-cure isocyanate-acrylate system

A combination of isocyanate–acrylate and hydroxylated acrylate monomers has been cured by heating and UV-irradiation in the presence of a cerium IV salt thermal initiator and an acylphosphine oxide photoinitiator. Both reactions (acrylic polymerization and polyaddition) were followed quantitatively by infrared spectroscopy through the decay of the characteristic IR bands at 2271 cm −1 (isocyanate) and 1410 cm −1 (acrylate double bond). The thermal curing was greatly accelerated in the presence of the cerium salt, which initiates the thermal polymerization of acrylate double bonds, a hard coating being obtained after a 15 min heating at 120 °C or 1 h at 80 °C (with an acrylate conversion of 80%). A 1-s UV exposure prior to the thermal treatment causes an extensive polymerization of the acrylates (94% conversion), but the reduced molecular mobility in the polymer network thus formed is slowing down the thermal cure. For the same reason, UV-irradiation of the thermally cured polymer is hardly promoting the polymerization of the remaining acrylate double bonds.

Multifrequency Time-Resolved Electron Paramagnetic Resonance Investigations after Photolysis of Phosphine Oxide Photoinitiators. Dependence of Triplet Mechanism Chemically Induced Dynamic Electron Polarization on Microwave Frequency

Phosphinoyl radicals were produced in benzene solution by photolysis of three acylphosphine oxide photoinitiators, diphenyl-2,4,6-trimethylbenzoyl phosphine oxide (I), bis(2,6-dimethoxybenzoyl)-(2,4,4-trimethylpentyl) phosphine oxide (II), and bis(2,4,6-trimethylbenzoyl) phenylphospine oxide (III). The chemically induced dynamic electron polarization (CIDEP) of the radicals was measured by time-resolved electron paramagnetic resonance spectroscopy at different microwave frequencies/magnetic fields, in S- (2.8 GHz, 0.1 T), X- (9.7 GHz, 0.34 T), Q- (34.8 GHz, 1.2 T), and W-bands (95 GHz, 3.4 T). The CIDEP was found to be due to a triplet mechanism (TM) superimposed by a radical pair mechanism comprising ST(0) as well as ST(-) mixing. Contributions of the different CIDEP mechanisms were separated, and the dependence of the TM polarization on microwave frequency was determined. It agrees well with the numerical solution of the relevant stochastic Liouville equation, which proves the TM theory quantitatively. The applicability of previous approximate analytical formulas for the TM polarization is discussed. Parameters of the excited triplet state of III were estimated from the dependence of the TM polarization on microwave frequency. They are zero-field splitting constant 0.169 cm(-1) </= D(ZFS) </= 0.195 cm(-1), lifetime 40 ps </= tau(T) </= 200 ps, and initial population of its T(z)() spin sublevel 0.92 </= w(z)() </= 1.

Photocrosslinking of functionalized rubbers. X. Butadiene–acrylonitrile copolymers

AbstractThe photocrosslinking of polyacrylonitrile‐block‐polybutadiene‐block‐polyacrylonitrile (ABA) was shown to proceed within seconds at ambient temperature upon UV exposure in the presence of an acylphosphine oxide photoinitiator. The curing process was followed by infrared spectroscopy, insolubilization, and hardness measurements. Complete insolubilization could not be achieved with the neat ABA rubber because of the poor reactivity of the 2‐butene double bond and the low vinyl content of the polybutadiene chain. The addition of multifunctional acrylate monomers (20 wt %) causes a substantial increase of both the reaction rate and the crosslink density of the polymer, which becomes completely insoluble in toluene in less than 1 s upon UV irradiation. An even greater effect was observed by using small amounts (1 wt %) of a trifunctional thiol crosslinker. Both the thiol and the photoinitiator concentrations were shown to affect the kinetics of the thiol–ene polymerization and the polymer network crosslink density. A direct relationship was found to exist between the swelling degree of the UV‐cured rubber and the interchain molecular weight of the network. © 2001 John Wiley &amp; Sons, Inc. J Appl Polym Sci 82: 2204–2216, 2001

Photocrosslinking of functionalized rubbers IX. Thiol-ene polymerization of styrene-butadiene- block-copolymers

A thermoplastic elastomer, polystyrene- block-polybutadiene- block-polystyrene (SBS) with a high vinyl content (59%), was crosslinked within a fraction of a second by UV-irradiation in the presence of a trifunctional thiol and an acylphosphine oxide photoinitiator. The curing process was followed by IR spectroscopy, insolubilization and hardness measurements. Both the thiol and the photoinitiator concentrations were shown to affect the kinetics of the thiol–ene polymerization. Insolubilization was found to occur even at very low concentrations in thiol (≤1 wt%) and in photoinitiator (0.1 wt%). The heat resistance of the photosensitive formulation is high enough at 150°C to allow this system to be used for hot-melt adhesive applications.

High-speed photocrosslinking of thermoplastic styrene-butadiene elastomers

Photoinitiated thiol/ene polymerization was used to crosslink a triblock styrene/butadiene/styrene (SBS) polymer of low vinyl content (8%). The crosslinking process was followed by infrared spectroscopy (loss of unsaturation), insolubilization, swelling, and hardness measurements. The photogenerated thiyl radicals react with both the vinyl and the 2-butene double bonds of the copolymer. Concentrations of less than 1 wt % in the trifunctional thiol crosslinker and in the acylphosphine oxide photoinitiator proved to be sufficient to create, within 0.5 s, a permanent chemical network in the elastomeric phase. This UV-curing technology was successfully applied to crosslink rapidly commercial SBS–Kraton® thermoplastic elastomers. It proved also effective in the case of the much less reactive triblock styrene/isoprene/styrene (SIS) polymer which contains no vinyl double bonds. The thiol/ene polymerization was shown to be a much more efficient process to crosslink SBS and SIS thermoplastic elastomers than was the copolymerization of the rubber double bonds with a diacrylate monomer. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1902–1912, 2000

Photocrosslinking of functionalized rubbers, 7. Styrene-butadiene block copolymers

The photocrosslinking of polystyrene-block-polybutadiene-block-polystyrene (SBS) was studied by means of infrared spectroscopy, by monitoring the disappearance of the pendent vinyl double bonds, which was shown to proceed within a few seconds upon UV exposure in the presence of an acylphosphine oxide photoinitiator. Complete insolubilization requires the reaction of 17 double bonds per polymer chain for an SBS sample containing 8% vinyl groups. An increase of the vinyl content has little effect on the crosslinking process, because it enhances mainly intramolecular reactions. A paraffinic oil proved to be an effective plasticizer for the photocrosslinked elastomer. The addition of a telechelic acrylate oligomer causes a substantial increase of both the reaction rate and the final degree of conversion of the SBS double bonds. The light-induced copolymerization of the vinyl and butene double bonds with the acrylate double bonds leads to the formation of a hard and flexible polymer material within a fraction of a second.

Photocrosslinking of functionalized rubbers, 7. Styrene-butadiene block copolymers

The photocrosslinking of polystyrene-block-polybutadiene-block-polystyrene (SBS) was studied by means of infrared spectroscopy, by monitoring the disappearance of the pendent vinyl double bonds, which was shown to proceed within a few seconds upon UV exposure in the presence of an acylphosphine oxide photoinitiator. Complete insolubilization requires the reaction of 17 double bonds per polymer chain for an SBS sample containing 8% vinyl groups. An increase of the vinyl content has little effect on the crosslinking process, because it enhances mainly intramolecular reactions. A paraffinic oil proved to be an effective plasticizer for the photocrosslinked elastomer. The addition of a telechelic acrylate oligomer causes a substantial increase of both the reaction rate and the final degree of conversion of the SBS double bonds. The light-induced copolymerization of the vinyl and butene double bonds with the acrylate double bonds leads to the formation of a hard and flexible polymer material within a fraction of a second.

Interpenetrating polymer networks. II. Sunlight-induced polymerization of multifunctional acrylates

Protective coatings and glass laminates have been readily obtained by sunlight-curing of acrylate monomers dispersed in a poly(methyl methacrylate) matrix or in a styrene–butadiene rubber, in the presence of an acylphosphine oxide photoinitiator. The polymerization reaction was followed by infrared spectroscopy and by gel fraction measurements and was shown to proceed extensively within minutes. As expected, the inhibitory effect of atmospheric O2 on such radical-initiated reactions was less pronounced in solid than in liquid samples. The monomer, photoinitiator, and plasticizer concentrations were found to have a strong influence on the rate of polymerization, the final degree of conversion, and the hardness of the sun-cured polymer. The adhesion of the cured coating on glass was substantially improved by the addition of an acrylate-grafted organosol silica. To produce strongly adhesive glass laminates, a photocurable acrylate resin was poured between two coated glass plates and exposed to sunlight for a few seconds. The same formulation can serve as a light-sensitive quick setting glue to bond glass to a variety of materials [polycarbonates, poly(vinyl chloride), aluminium, and steel]. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2269–2282, 1998

Interpenetrating polymer networks. I. Photopolymerization of multiacrylate systems

AbstractThe light‐induced polymerization of a triacrylate monomer (TMPTA) has been carried out in a polymer matrix to generate a semi‐interpenetrating polymer network (IPN). The reaction kinetics was followed by IR spectroscopy for the various polymer binders studied: poly(vinyl chloride) (PVC), poly(methyl methacrylate), polystyrene, and crosslinked polyurethane. Under intense illumination, crosslinking occurred extensively within a fraction of a second, with formation of a hard and highly resistant polymer material. These semi‐IPNs were found to be essentially insoluble in the organic solvents, thus indicating that the acrylate network is grafted onto the polymer matrix, probably because of an efficient chain transfer process. The monomer and photoinitiator concentration, as well as the light intensity were shown to have a great influence on both the rate of polymerization and the final degree of conversion. By using an acylphosphine oxide photoinitiator, PVC–;TMPTA blends have been cured within a few minutes in an accelerated QUV‐A weatherometer, which emits low‐intensity UV radiation similar to sunlight. © 1994 John Wiley &amp; Sons, Inc.