Naphthoylenebenzimidazolone dyes as one-component photoinitiators

The appropriate substituents have been added to a 7H-benzimidazo[2,1-a]benz[de]isoquinolin-7-one skeleton in order to obtain a one-component initiator system. The absorption, fluorescence, and electrochemical properties of these naphthoylenebenzimidazolone dyes and their usefulness as visible light initiators of free radical polymerisation of trimethylolpropane triacrylate were examined. The initiation efficiency of these dyes was compared with that of the parent 7H-benzimidazo[2,1-a]benz[de]isoquinolin-7-one in the presence of a coinitiator. Results show that these bifunctional dyes are able to initiate polymerisation without an additional coinitiator. Photopolymerisation studies and the relationship between the rate of polymerisation and the free energy change for electron transfer revealed that, depending on the concentration, initiating radicals are generated via intra- and intermolecular electron transfer.     

Keto-sulfoxide derivatives as photoinitiators of polymerization

The photolysis of three aryl—alkyl sulfoxide photoinitiators is studied by time-resolved laser spectroscopy. The general diagram of the excited-state process is rather unusual: it shows a dual path of photolysis. Thus, whereas the singlet state cleaves at the S-alkyl bond, the triplet generates aryl and alkyl sulfinyl radicals. The conclusions arrived at are corroborated by product analysis by the coupled gas chromatography—mass spectroscopy technique. The photoinitiated polymerization activity has been checked and compared with that of other well known photoinitiators.     

Thioxanthone-containing renewable vegetable oil as photoinitiators

Soybean oil containing thioxanthone (TX) moieties and/or coinitiator DBA (ESO-ATX-DBA, ESO-ATX/ESO-DBA) were synthesized by grafting 2-acitic thioxanthone (ATX) and 4-(dimetheylamino) benzoic acid (DBA) to the backbone of epoxidized soybean oil (ESO). The obtained ESO-ATX-DBA, ESO-ATX and ESO-DBA were characterized by FT–IR, ¹H NMR and UV–vis spectra, and investigated as photoinitiators by photo-DSC. Photoinitiator systems ESO-ATX-DBA and ESO-ATX/ESO-DBA were more efficient than their low-molecular weight analogues (chemical mixture of ETX-DBA and physical mixture of ETX/EDB) especially in the photopolymeriztion of acrylate monomers containing pigment. Moreover, ESO-ATX-DBA exhibited much lower migration in comparison with their low-molecular weight analogues. These characteristics gave the obtained TX containing soybean oil potential in the application of ink, and these studies also provide alternative approach to prepare polymeric photoinitiators from the renewable source.     

Ketonic resins as free radical photoinitiators

Photoreactive cyclohexanone‐formaldehyde and acetophenone‐formaldehyde resin‐bound benzoin and benzoin isobutyl ether resins were successfully prepared by the method of in situ modification of ketonic resins. These photoinitiators were used to polymerize styrene using UV lamp with wavelength of 350 nm. Initiating efficiencies of ketonic resin‐bound benzoin and benzoin ether were much higher than benzoin and benzoin ether. The products were ketonic‐resin‐polystyrene block copolymers. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 927–934, 1999     

Thioxanthone derivatives as photoinitiators in micelle photopolymerization

This paper provides a complete survey of the primary processes involved in typical oil-and water-soluble thioxanthane derivatives dissolved in sodium dodecyl sulfate micelles, in the presence of monomers and amines. Special emphasis is laid on the determination of the rate constants of the different processes and the absorption spectra of the transients. Relevant data are shown and discussed with reference to the effectiveness of these molecules as photopolymerization initiators.     

Quinoxaline derivatives as photoinitiators in UV-cured coatings

Photopolymerization of multifunctional acrylates with a series of quinoxaline derivatives as photoinitiator with N-methyldiethanol amine (MDEA) has been investigated by real-time Fourier transform infrared spectroscopy (RT-FTIR). The formulations were also coated onto tracing paper and cured by using Mini-UV-Cure unit. Curing was assessed until no visible deformation was observed. MEK resistance of films was also determined.     

Substituted vinyl bromides as photoinitiators for cationic polymerizations

Summary The cationic polymerization of typical monomers, e.g. of oxiranes such as cyclohexene oxide and 1,4-butanedioldiglycidyl ether or of vinyl ethers such as n-butylvinyl ether, is induced by UV irradiation of monomer formulations containing a substituted vinyl bromide as light absorbing agent and an appropriate non-absorbing onium salt. Experiments performed with 1,2,2-triphenyl vinyl bromide or 1,2,2-tri(4-methoxyphenyl) vinyl bromide and N-ethoxy-2-methyl-pyridinium or triphenyl sulfonium hexafluorophosphate are described in the paper.     

Photosensitive resins containing p-dimethylaminobenzylidene derivatives and diphenyliodonium salt as photoinitiators

A series of p-dimethylaminobenzylidene derivatives was able to sensitize the photodecomposition of diphenyliodonium salt to afford highly photosensitive negative-type resins. When a polymer-bearing methacryloylated group in the side chain was sensitized with a combination of the p-dimethylaminobenzylidene compounds and the iodonium salt, the polymer demonstrated high sensitivity even to 488 nm light emitted from an Argon laser. The same photoinitiator systems were applicable to insolubilize poly(glycidyl methacrylate) through cationic photopolymerization. The storage stability of these types of photoinitiators depends on the structure of the benzylidene compounds; decreasing the basicity of the amino group enhanced the thermal stability.     

Quinolineimidazopyridinium derivatives as visible-light photoinitiators of free radical polymerization

Several dyes containing Quinolineimidazopyridinium moiety (QIPD) have been synthesized and evaluated as photoinitiators for free radical polymerization induced with the visible emission of a commercial dental lamp. The tested dyes were tested as photoinitiators in the presence of selected electron donors. Different substituents introduced into both the pyridine ring and quinoline moieties of the dyes influence photophysical properties of the investigated systems. Several different groups were tested including heavy atoms (–Cl, –Br, –I) and electron accepting (–NO₂) group. Analysis of the properties of the tested dyes allows one to conclude that there is a significant heavy atom effect on their photoinitiation efficiency. The type of the applied counter-ion has no effect on the overall performance of the photoinitiating system. QIPDs possess broad structured spectra with long-wavelength part located at the boundary of visible and UV parts of light spectrum. This makes QIPDs good candidates for the use as photoinitiating systems for dental restorative materials.     

Bisacylphosphine oxides as bifunctional photoinitiators for block copolymer synthesis

Block copolymers of styrene (St) and methyl methacrylate (MMA) were prepared via a two-step procedure by using bisacylphosphine oxide (BAPO) as photoinitiator. Photolysis of BAPO at λ = 420 nm in the presence of St yielded polymers with monoacylphosphine oxide terminal groups. Subsequent irradiation of the polymers in the presence of MMA at λ = 380 nm produced block copolymers. Block copolymer formation was evidenced by spectral measurements and GPC analysis.     

Novel sulfonium salts as thermal and photoinitiators for epoxide and acrylate polymerizations

Novel sulfonium salts, 1‐naphthylmethyl‐, cinnamyl‐, 9‐fluorenyl tetramethylene sulfonium hexafluoroantimonates, and dimethylsulfonium hexafluoroantimonates, were synthesized by the reaction of tetrahydrothiophene and dimethylsulfide with the corresponding bromides or chloride, followed by anion exchange with KSbF₆. These sulfonium salts polymerized epoxy monomers at a temperature lower than previously reported for benzyltetramethylenesulfonium hexafluoroantimonate. They initiated radical photopolymerization as well as cationic polymerization. The photopolymerization was accelerated by the addition of aromatic compounds such as p‐methoxyphenol, 4‐methoxy‐1‐naphthol, 2‐ethyl‐9,10‐dimethoxyanthracene, N‐ethylcarbazole, and phenothiazine as photosensitizers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 589–597, 2004     

Diacetoxyiodobenzene and bis(trifluoroacetoxy)iodobenzene as photoinitiators for cationic polymerisations

Summary It is shown that i-butyl vinyl ether, tetrahydrofuran, epichlorhydrin and cyclohexene oxide, which undergo typically cationic polymerisation, are polymerised by UV-irradiation in the presence of diacetoxyiodobenzene or bis(trifluoroacetoxy)iodobenzene.     

Supported photosensitizers as new efficient materials for gas-phase photo-oxidation

The photosensitised oxidation of dimethylsulfide in the gas phase was carried out for the first time on original silica materials in a flow reactor and under visible light irradiation. The photocatalysts were prepared either by physisorption of two different photosensitizers, 9,10-dicyanoanthracene or 9,10-anthraquinone on commercial silica beads, or by incorporation of 9,10-dicyanoanthracene in sol–gel monoliths. Oxidation products are mainly sulfoxide, sulfone and disulfide, and it is assumed that singlet oxygen is the most probable reactive oxygen species.

These materials display several advantages as they are activated by visible light, and they act as very efficient traps for partially oxidized products. Accordingly, the gas-flow at the outlet of the photocatalytic device is free of any toxic or nauseous product for several days. As soon as products appear in the gas flow, the catalyst is deactivated, but the silica beads can be easily regenerated by mild thermal treatment under controlled conditions.

With regard to the photo-oxidative efficiency, our results point out the influence of the properties of the silica support itself, such as transparency, homogeneity and specific surface area. The adsorption capacity of the material is a crucial parameter, as the most DMS adsorbing material is also the most efficient.     

Recent developments in photoinitiators

A new photoinitiator, bis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentylphosphine oxide (1), has been developed for industrial applications. The absorption of this bisacylphosphine oxide (BAPO) compound in the near UV-Vis range is significantly higher than that of hitherto known photoinitiators for UV curing. Investigation of the photochemistry of 1 revealed the efficient formation of four radicals, which can all initiate polymerization. Since the photoreaction is accompanied by the destruction of the chromophore responsible for absorption in the near UV-Vis, photobleaching of the long wavelength absorption is observed and the photoinitiator does not impart yellowing in the cured lacquer. Studies using FTIR and RTIR techniques showed that these features result in a higher conversion of acrylic double bonds than obtained with other photoinitiators in formulations containing a high loading of rutile type titanium dioxide pigments. These findings were confirmed by application tests in different white pigmented coatings. Further, the new photoinitiator allows the fast curing of thick pigmented layers, which makes it suitable for use in pigmented furniture coating. This new class of high performance photoinitiators is expected to promote the development of UV curable white coatings of high opacity and other applications where light in the near UV-Vis range is essential for curing. A liquid containing 25 parts of the BAPO photoinitiator 1 and 75 parts of 2-hydroxy-2-methyl-l-phenyl-propan-l-one (2) is an excellent technical and economical solution for most applications.

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Study of methoxyphenylquinoxalines (MOPQs) as photoinitiators in the negative photo-resist

To develop photoinitiator systems of high performance for the negative photo-resist, we synthesized six methoxyphenylquinoxalines (MOPQs) and investigated the photopolymerization of 2,2-bis(4-(acryloxypolyethoxy)phenyl)propane (A-BPE-10) initiated by these MOPQs in the negative photo-resist. MOPQs possess suitable UV–vis maximum absorption wavelengths in the range of 349–402 nm, along with high extinction coefficients ?. Except for T3MOP-DQ and T4MOP-DQ, the other four MOPQs, D3MOP-Q, D4MOP-Q, D3MOP-BenQ and D4MOP-BenQ, could initiate photopolymerization of A-BPE-10 in the negative photo-resist very efficiently. In particular, D3MOP-BenQ was the most efficient, with almost 100% final conversion in the presence of 2-mercaptobenzothiazole (MBO) as a coinitiator. Among the four coinitiators LCV, MBO, NPG and MDEA, MBO was the best coinitiator for MOPQs. The negative photo-resist containing MOPQs as a photoinitiator can also form good patterns on copper through photolithography. These characteristics make MOPQs potential photoinitiators in the negative photo-resist.     

The dyes possessing diazine residue as effective photoinitiators of free radicals polymerization

Summary The series of the dyes possessing diazine residue have been investigated as visible-light absorbing photoinitiators of free radical polymerization. The rates of photoinitiation depend on the structure of the dye. Mechanism of the photoinitiation involves the electron transfer process between the dye and the electron donor (co-initiator). The dyes possessing diazine residue in the presence of a suitable electron donor are very effective photoinitiators. This can be attributed to the high quantum yield of their triplet state formation and high rate constant of electron transfer reaction between the dye and electron donor.     

Visible laser lights in photoinduced polymerization. VI. Thioxanthones and ketocoumarins as photoinitiators

The efficiency of thioxanthones and ketocoumarins as photoinitiators has been checked in visible laser light-induced polymerization reactions and discussed in terms of excited-state reactivity (as revealed by time-resolved laser spectroscopy). These compounds undergo fast electron transfer reaction in the presence of amines and onium salts. Transient absorption spectra and rate constants of the processes involved have been determined. The combination photoinitiator-amine-onium salt appears as very promising for the design of efficient photosensitive systems.