Acetophenone photoinitiator

Figure 18 Phosphorescence spectra of a 1 1 (by weight) acrylate-based TMPTA/ PMMA 0.25-mm thin film containing an acetophenone photoinitiator and fac-ClRe(CO)3(4,7-Ph2-phen) as a function of UV exposure (A) 0 s, (B) 5 s, (C) 10 s, (D) 20 s, (E) 30 s, and (F) 60 s. Excitation wavelength is 420 nm. (From Ref. 100.)...

The high performance of these -amino substituted acetophenone photoinitiators is best explained by the fact that both possess sufficient absorption in the region where the incident light is not filtered by the pigment. 

Acetophenone can react with formaldehyde to yield light-resistant resins which are used as additives in nitrocellulose paints. It is also used as a photoinitiator, and in the pharmaceuticals, perfumery, and pesticide industries (344). It can be hydrogenated to 1-phenylethanol which is used for the production of aromatic ester fragrances (345). Technical-grade acetophenone is available at 2.29/kg perfume-grade acetophenone was 6.50/kg in October 1994. 

Ultraviolet Photoinitiators. Photoinitiators are used in increasing volume for a multitude of appHcations. The most important of these are in the formulation of uv-curable inks and in the production of coatings on vinyl flooring, wood, and electronics components (28,29). The most common types of photoinitiators are phenone derivatives, for example, acetophenones and hen 7ophen ones (30). 

When free-radical initiation is used, cocatalysts, eg, phosphites (112), and uv photoinitiators such as acetophenone derivatives (113) can be used to increase the rate and conversion of the olefins to the desired mercaptans. 

The chemistry involved in LfV-curable resin systems has been extensively investigated and thoroughly surveyed [88-94]. LfV-radiation polymerization, is in principle, completely analogous to the conventional addition polymerization. A photoinitiator is used in UV polymerization. Its function is the same as the free-radical initiator. A conventional initiator possesses a thermally labile bond which is cleaved to form free-radical species, but the photoinitiator has a bond which breaks upon absorption of radiant energy. Benzoin ethers, benzyldialkyl ketals, benzophenone, and acetophenone derivatives are the important LfV-photoinitiators [95-99]. 

Trimethylolpropane triacrylate (TrMPTrA, mw 296.3, Polysciences Inc., Warrington, PA) was mixed with 1 wt% 2,2-dimethoxy-2-phenyl-acetophenone (DMPA, mw 256.3, Aldrich Chemical Co., Milwaukee, WI) as a photoinitiator. For... 

In this work, the kinetics of these reactions are closely examined by monitoring photopolymerizations initiated by a two-component system consisting of a conventional photoinitiator, such as 2,2-dimethoxy-2-phenyl acetophenone (DMPA) and TED. By examining the polymerization kinetics in detail, further understanding of the complex initiation and termination reactions can be achieved. The monomers discussed in this manuscript are 2-hydroxyethyl methacrylate (HEMA), which forms a linear polymer upon polymerization, and diethylene glycol dimethacrylate (DEGDMA), which forms a crosslinked network upon polymerization. 

When using a suitable type I photoinitiator, e.g., acylphosphine oxides and non-amine-containing acetophenones in this system, the polymerization process is very efficient and the resulting product is a 1 1 alternating copolymer. This system is susceptible to oxygen inhibition, but to a much lesser extent than acrylate polymerization. An important advantage of this system is its low toxicity. Typical components include a variety of vinyl ethers and unsaturated esters, such as maleate, fumarate, citra-conate, imides (maleimides), or N-vinylformamides. The system is also... 

Based on the known photoreduction chemistry of Rose Bengal [275], one would anticipate that electron transfer would reduce the xanthene skeleton of RBAX and that the radical anion thence formed might decay by the elimination of an acetyl radical. Acetyl is totally analogous to benzoyl, the radical that initiates chains in the case of most Norrish type I UV photoinitiators, that is, benzoin ethers or acetophenone acetals. The putative scheme is shown in Scheme 7. 

The addition of cyclic ethers to terminal olefins can be induced directly by light (21). However, the yields in this reaction are relatively low and light of relatively short wavelengths must be applied. Through the use of photoinitiators, such as acetone and acetophenone (17), this addition reaction becomes of synthetic value. Thus, cyclic ethers add to terminal olefins under ultraviolet irradiation in the presence of a ketonic photoinitiator to yield the alpha-alkalyted cyclic ethers,... 

When using photoinitiators such as phenyl acetophenone derivatives, addition of an hydrogen donating solvent (Table IV) to the system improved ultimately the percent grafting and, in addition, the concentrations of initiator required were lower. Moreover, the presence of THF is necessary with benzophenone derivatives. These results are in agreement with similar observations with respect to MMA polymerization in solution in fact, the rate of polymerization was enhanced in the presence of THF. 

In photoinitiated reactions, the reactivity of the substrate-nucleophile pair can be modified by changing the solvent and the irradiation source. For instance iodobenzene does not react under irradiation (pyrex-filtered flask) with acetophenone enolate anion in liquid ammonia [21], but it does react in DMSO [22]. However, the reaction occurs in liquid ammonia by irradiation in an immersion well [23]. 

Recently, Ledwith described combined systemscomposed of a radical initiator and a cationic photoinitiator, which are very suitable for hybrid systems. It is particularly convenient to employ common photochemical sources of free radicals for this purpose. Since many of them possess aromatic carbonyl groups (e.g. benzoin and acetophenone derivatives), these groups provide an extension of the absorption to longer wavelengths and promote the initiation of cationic polymerization. Figure 19 shows the proposed formation mechanism of free-radical and cationic active species by electron transfer ... 

In the photopolymerization of methacrylamide by benzoin methyl ether, chain-transfer to monomer has been found to be important, and benzalde-hyde is reported to be an inefficient photoinitiator of methyl methacrylate polymerization unless benzophenone and triethylamine are present. Acetophenone has been found to sensitize the cycloaddition of maleic anhydride to 7-oxabicyclo[2.2.1]heptan-5-one-2,3-dicarboxylic anhydride, , a-hydroxy-acetophenone derivatives have been found to be non-yellowing initiators, and h.p.l.c. has been used to determine residual carbonyl photoinitiators in u.v.-cured resins. In the emulsion-polymerization of methyl methacrylate using an aromatic ketone and a continuous or intermittent laser, the former conditions were found to be similar to those under continuous u.v. irradiation. The dependence of the polymerization rate and average chain-length on the absorbance of the initiator used in the photoinitiated polymerization of vinyl monomers has been studied. Interestingly, irrespective of all conditions, maximum conversion is observed when initiator absorbance is 2.51. "... 

An oligomeric polysiloxane photoinitiator (PSDAP) containing dialkoxy acetophenone moieties, prepared by reacting diallyloxy-acetophenone with penta-methyl-disiloxane and H-terminated dimethyl-silicone in the presence of chloro-platinic acid, has been claimed [87] to be compatible with silicone prepolymers containing methylvinyl siloxane co-units and active in their UV curing. 

As with the previous reported conclusion concerning the polymeric photoinitiators based on hydroxyalkyl acetophenone moiety (KIP), in this case rm (Eq. 4) also is much higher in the polymeric systems than in the models (Table 22), indicating that the B radicals anchored to the polymer backbone are less prone to give radical-radical combination, thus favouring flieir reaction with the acrylic monomers. 

All the MBA/A(,iV-dialkylamino acrylate copolymers behave similarly to poly(MBA-co-MtA)s (Tables 21 and 25), thus suggesting that the replacement of MtA by A,A(-dialkylamino acrylate co-units does not markedly affect the photoinitiation activity of the system. Accordingly, BMI/A,A(-dialkylamino isobutyrates mixtures exhibit substantially the same activity as MBI alone [118]. Similar results have previously been obtained for 2,2-dimethoxy-2-phenyl acetophenone (DMPA), when additioned with diethylmethylamine, in the UV initiated polymerization of -butyl methacrylate [113]. However, a remarkable shortening of the induction period (to) of UV curing is observed for all the polymeric photoinitiators in the presence of tertiary amines as compared with the low-molecular-weight MBl/A,A(-diatkylamino isobutyrates systems, the maximum effect resulting in the case of MBA/A(,iV-dialkylamino acrylate copolymers (Table 25). 

UvlmerTM 530 and the other members of the UvlmerTM series may be cured with benzoin ether type photoinitiators and with diethoxy acetophenone. Table III presents data on the cure speed of UvlmerTM 530 formulated with butyl benzoin ether. These data were obtained in air without the use of Inert blanketing. Films of 3 mil thickness were irradiated on a moving belt using a 5000 watt Addalux uv lamp (Berkey Photo, Inc.) focussed on one linear Inch, This Is a low pressure lamp Incorporated In an experimental unit. Faster cure speeds (up to 200 ft. per mlnute/lamp) were obtained in later studies with a unit employing two medium pressure, 200 watts/llnear inch Hanovia lamps. 

If one desires to optimize the yield of mercaptan, there needs to be a large excess of H2S used in the process. Acetophenone and its derivatives such as 2,2 -diethoxyacetophenone and benzoin ethyl ether, and organic phosphites are a few photoinitiators that... 

Photoinitiation System. In most cases the curing is initiated by free radicals generated by UV light and photoinitiators. The free radicals can be formed from photocleavage or hydrogen abstraction mechanisms. Benzoin ethers, benzil ketals, and acetophenone derivatives are typical photoinitia,tors. 

Benzoin Ethers Benzoin ethers were the most widely used photoinitiators for a long time [13-15]. The cleavage process in the triplet state (10.8) is very fast compared to that of some related structures (>1010 s ). The cleavage yield is almost unity for 2,2-dimethoxy—2 phenyl-acetophenone DMPA or 2-methoxy -2 phenyl acetophenone BME. A secondary photochemical cleavage (the possible thermal cleavage is less efficient) can arise in the dimethoxy benzyl radical and leads to a methyl R" radical and an alkyl benzoate. 

Kinetics of the Cleavage Process in Type I Photoinitiators Working now on the picosecond timescale (with a pump-probe laser setup) shows the shortlived transient absorptions observed upon light excitation [250], For example [251], the cleavage process of DMPA (2,2-dimethoxy -2 phenyl-acetophenone) occurs... 

Phan X.T. (1986) Photochemical a-cleavage of 2,2-dimethoxy-2-phenyl-acetophenone and 1-hydroxy-cyclohexyl-phenyl ketone photoinitiators. Effect of molecular oxygen on free radical reaction in solution. J. Radiation Curing, 13, 18-25. 

Photoinitiated hydrosilation of acetophenone with triethylsilane occurred in the presence of the clusters 7... 

Homogeneous photoinitiated hydrosilation of acetophenone has been catalyzed by... 

Other acetophenone derivatives that have been proposed include 1-benzo-cylcohexanol, 4-methylmercapto-a,a-dimethyl-morpholino-acetophenone, which has a much stronger absorption at 365 nm than other benzoin ethers (s lO L/ mole cm) and is therefore suitable as a photoinitiator for highly pigmented coat-... 

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