Sulfonium triaryl

Protonic initiation is also the end result of a large number of other initiating systems. Strong acids are generated in situ by a variety of different chemistries (6). These include initiation by carbenium ions, eg, trityl or diazonium salts (151) by an electric current in the presence of a quartenary ammonium salt (152) by halonium, triaryl sulfonium, and triaryl selenonium salts with uv irradiation (153—155) by mercuric perchlorate, nitrosyl hexafluorophosphate, or nitryl hexafluorophosphate (156) and by interaction of free radicals with certain metal salts (157). Reports of "new" initiating systems are often the result of such secondary reactions. Other reports suggest standard polymerization processes with perhaps novel anions. These latter include (Tf)4Al (158) heteropoly acids, eg, tungstophosphate anion (159,160) transition-metal-based systems, eg, Pt (161) or rare earths (162) and numerous systems based on tri flic acid (158,163—166). Coordination polymerization of THF may be in a different class (167). 

Fig. 9. Initiation of epoxy cure. Irradiation of a triaryl sulfonium salt produces a radical cation that reacts with an organic substrate RH to produce a cation capable of releasing a proton. The proton initiates ring-opening polymerization. X = BF , PFg, AsFg, and SgFg. ...

While electron beams can produce cations, they are not effective at producing cationic cure in the absence of suitable photoinitiators. The same cationic photoinitiators used for UV cure are often also e-beam sensitive. Examples are triaryl sulfonium or diaryl iodonium salts [41]. 

Use of a Difunctional Crosslinker. An alternate approach to chemically amplified imaging through electrophilic aromatic substitution is shown in Figure 6 below. In this approach a polyfunctional low molecular weight latent electrophile is used in a three component system also including a photoactive triaryl sulfonium salt and a phenolic polymer. In this case again crosslinking of the polymer is observed upon... 

This basic approach to chemical amplification was subsequently extended by Ito et al. [3] through resist formulations incorporating appropriately chosen triaryl sulfonium or diaryliodonium salt. For example, end-capped poly(phthalaldehyde) used in combination with an onium salt photoacid generator is an excellent self-... 

As an analogous example, the behavior of sulfonium salts can be mentioned. At mercury electrodes, sulfonium salts bearing trialkyl (Colichman and Love 1953) or triaryl (Matsuo 1958) fragments can be reduced, with the formation of sulfur-centered radicals. These radicals are adsorbed on the mercury surface. After this, carboradicals are eliminated. The carboradicals capture one more electron and transform into carbanions. This is the final stage of reduction. The mercury surface cooperates with both the successive one-electron steps (Scheme 2.23 Luettringhaus and Machatzke 1964). This scheme is important for the problem of hidden adsorption, but it cannot be generalized in terms of stepwise versus concerted mechanism of dissociative electron transfer. As shown, the reduction of some sulfonium salts does follow the stepwise mechanism, but others are reduced according to the concerted mechanism (Andrieux et al. 1994). 

Scheme VI. Processing of poly(t-BOC-styrene)-onium salt resists. The steps are (1) photogeneration of an extremely strong protonic acid from a triaryl-sulfonium or diaryliodonium salt and (2) baking, which allows acid-catalyzed deblocking of the t-BOC groups. Thus, irradiated areas of the polymer are converted to a much more polar form.

Cationic photoinitiators are frequently found in classes of compounds such as the triaryl sulfonium, tetraaryl phosphonium, and diaryliodonium salts of large protected anions (hexafluorophosphates or antimonates). These compounds are soluble in most epoxy resins, do not activate epoxy cure until exposed to uv light, are insensitive to room lighting, and have long storage life at room temperature. Cationic photoinitiators form an acid catalyst when exposed to uv light and consequently start the cationic chemical reaction. 

Figure 7. Example calculation of AG. Free-energy calculations ( G) show that electron transfer from triplet excited thioxanthane to the diaryliodonium salt is exothermic, and therefore, sensitization is observed. In contrast, electron transfer from triplet excited thioxanthane to the triaryl-sulfonium salt is endothermic thus, sensitization is not observed.

The bulky anion then stabilizes the intermediate adduct from protonation of the epoxy group and then facilitates insertion of epoxide at the cationic propagation site. Rapid polymerization can then occur. Cationic photopolymerization of epoxides often involves the photo-generation of acid from an initiator such as diaryliodonium or triaryl sulfonium salts (Crivello, 1999). The anions are important in controlling the addition at the cationic site and are typically BF4 and PFg. The reactivity of the system depends also on the structure of the epoxide. 

Inhibition of the polymerization by air was controlled by use of 1 1 diacrylate-poly (methyl methacrylate) mixtures or by using the acrylate in a laminate between two glass plates. These cost-effective cures use no external energy and no lamps. Composites of glass fiber and epoxides from vegetable oils have been cured in sunlight with di-aryliodinium and triaryl sulfonium salts in 25 min.311 Further work is needed to speed up this photocationic cure. 

However, Trost et ah treated triaryl sulfonium salts with aryl lithiums to obtain only diaryl sulfides and diaryls, via sulfuranes [38]. These two contradictory results obtained by different groups have not been resolved. 

Sulfonium Salts Triaryl sulfonium salts (TPSs) are generally produced by the method of Pitt [23]—a Friedel-Crafts condensation of aromatic hydrocarbons with... 

It should be pointed out that the photolysis of the diaryliodonium and triaryl-sulfonium salts proceeds differently from the photolysis of the diazonium systems. The reaction mechanism of the photolysis of iodonium salts is described by Reactions [6.46] and [6.47]. 

Chem. Descrip. Triaryl sulfonium hexafluorophosphate (50%) in propylene carbonate... 

Triaryl sulfonium hexafluoroantimonate Properties Dens. 1.390 ref. index 1.4960 Toxicology Irritating to eyes, skin, respiratory system sensitizer possible mutagen TSCA listed... 

Methyl-1 -[4-(methylthio) phenyl]-2-morpholinopropan-1-one [4-(4-Methylphenylthio) phenyl]-phenylmethanone Oligo [2-hydroxy-2-methyl-1-[4-(1-methylvinyl) phenyl] propanone] Triaryl sulfonium hexafluoroantimonate Triaryl sulfonium hexafluorophosphate Tribromomethyl phenylsulfone 2,4,6-Trimethylbenzophenone 2,4,6-Trimethylbenzoyldiphenylphosphine oxide photoinitiator, conformals... 

Methylbenzophenone [4-(4-Methylphenylthio) phenyl]-phenylmethanone Triaryl sulfonium hexafluoroantimonate Triaryl sulfonium hexafluorophosphate 2,4,6-Trimethylbenzophenone photoinitiator, lacquers... 

Diazonaphthoquinones Nitrobenzylsulfonates Triaryl sulfonium salts (O3 S+ SbFg) Diphenyliodonium salts Polymer types... 

Table 1. Structure and Spectral Properties of Triaryl-sulfonium Salts...

Cat ionics Triaryl sulfonium, diazonium, or phosphonium salts, usually fluoborates... 

The decomposition mechanism of the triaryl sulfonium salt is believed to take place somewhat similarly... 

This modifieation does extend the sensitivity to longer wave length ultraviolet light. The eompounds were reported to display exeellent thermal lateney in the presence of various monomer systems and high effieieney as photoinitiators for cationic polymerization. Furthermore, their initiation efficiency was reported to be on par with current commercial triaryl sulfonium salts. 

Shim et al., reported preparation of several novel mono- and di-propenyl ethers by condensation of perfluoroalkyl alcohol with allyl bromide followed by the ruthenium-catalyzed isomerization of the corresponding allyl ethers. These fluorinated propenyl ethers undergo rapid photoinitiated cationic polymerization with the aid of triaryl-sulfonium salt bearing a long alkoxy... 

Diaryl iodonium and triaryl sulfonium salts are among the most versatile photoinitiators. These compounds have been thoroughly investigated by Crivello... 

Few photoinitiators are available for cationic systems. The most widely used are diaryl iodonium salts such as diaryliodonium hexafluoro-antimonate, triaryl salts such as triphenyl sulfonium hexafluoro-phosphate, and mixed triphenyl sulfonium salts. These photoinitiators are decomposed by UV light by a homolytic cleavage to produce a radical anion and a radical cation. The latter abstracts hydrogen from surrounding molecules and generates a proton, which is the initiating species ... 

Photochemical doping involves treating a CP with a dopant which is initially inert but rendered an active dopant by irradiation. These dopants are usable with common CPs. Examples are diphenyliodonium hexafluoroarsenate (in CH2CI2) or triaryl-sulfonium salts (in aqueous medium), both of which are rendered active by UV radiation [125, 126]. 

In all cases, these photoinitiators were less efficient than diaryliodonium and triaryl-sulfonium salts under comparable conditions. To date, there has been no report of a study of the mechanism of photolysis of these compounds nor have the quantum yields been determined. Since thiopyrylium salts are colored compounds, they may be useful photoinitiators in the visible region of the spectrum. The related thio-xanthylium salts were also examined as potential photoinitiators but were too hydrolytically unstable to be useful... 

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