Triarylsulfonium salts

Triarylbismuth dilahides, 4 31-33 Triarylbismuthines, 4 26-28 Triaryl carbonium dyes, 9 259-261 Triaryl phosphates, 11 493-494 Triarylpyrazolines, 19 113 Triarylstibines, 3 69 Triarylsulfonium salts, photolysis of,... 

UV spectra of both polymers IV and V taken from ca. ljim thick films showed that the each of the polymers had absorbencies of less than 0.30 per micron of film thickness at 254 nm as shown in Figure 6 for polymer V. This allows their use with triarylsulfonium salts, which generally absorb in the deep UV. In addition, it is known that poly(4-hydroxystyrene) does not absorb strongly in the deep UV, while poly(3,5-dimethyl-4-hydroxystyrene) also shows no strong absorption band near 254 nm (Figure 6). 

Diaryliodonium and triarylsulfonium salts act as photoinitiators of cationic polymerization. Photolytic celeavage of an Ar—I or Ar—S bond yields a radical-cation (Eq. 5-8) that reacts with HY to yield an initiator-coinitiator complex that acts as a proton donor to initiate... 

Lewis acids such as BF3 and SbCl5, almost always in conjuction with water or some other protogen, initiate polymerization of cyclic ethers. The initiator and coinitiator form an initiator-coinitiator complex [e.g., BF3 H20, H+(SbCl6) ], which acts as a proton donor (Sec. 5-2a-2). Cationic photopolymerizations are achieved when similar proton donors are formed by the photolysis of diaryliodonium and triarylsulfonium salts (Sec. 5-2a-4). 

Crivello (lib) has described a series of diaryliodonium (107) and triarylsulfonium salts (108) which function as initiators for ultraviolet activated cationic polymerization. The... 

For ihe photodecomposition of triarylsulfonium salts 2, Scheme 2 has been postulated 3). 

Such compounds as polynuclear aromatics, heteroaromatics, ketones, quinones and dyes can serve as donors. Both excited singlet and triplet-states of these products can be involved in the PET. Diaryliodonium salts, triarylsulfonium salts, phosphonium salts, ammonium salts, pyrylium and thiapyrylium salts possess enough thermal stability and corresponding reduction potential to function as electron acceptors (R X+). In order to select suitable photoinitiator systems based on compounds discussed, the Weller-Eq. (5) can be employed. 

Photoinitiators which produce species-inducing cationic polymerization of alkenes and heterocycles are usually based on diarylhalonium salts and triarylsulfonium salts [203]. The mechanism of the direct photolysis of these salts is quite complex and involves formation of excited singlet species which can reversibly convert by intersystem crossing (ISC) to the... 

Many different photoinitiators based on onium -type compounds with anions of low nucleophilicity also have been described in the literature as effective catalysts for the polymerization of epoxides Thus, diaryliodonium salts diaryliodosyl salts triarylsulfonium salts and related compoundstri-phenylsulfoxonium saltsdialkylphenacylsulfonium salts and dialkyl-4-hydroxyphenylsulfonium salts seem to be most suitable as photoinitiators for epoxy curing. Some of the principles of the reaction mechanism involving these initiators are discussed in detail in the following Sections. Various other onium photoinitiators such as diarylchloronium and diarylbromonium salts , thiopyrylium salts 3), triarylselenonium salts and onium salts of group Va elements >... 

The photolysis of dialkylphenacylsulfonium salts and dialkyl-4-hydroxyphenyl-sulfonium salts is different from that of triphenylsulfonium salts. The latter compounds undergo irreversible photoinduced carbon-sulfur bond cleavage the former compounds, however, react by reversible photodissociation and form resonance-stabilized ylids as shown in Fig. 5. Because of the slow thermally induced reverse reaction, only small equilibrium concentrations of the ylid and acid arc present during irradiation and the concentration will rapidly decrease when photolysis has been terminated. Therefore, in contrast to triarylsulfonium salt initiation, no dark reaction will continue after the irradiation step. 

Our newly described family of thermally labile polycarbonates operate on a somewhat similar design [10]. The system is based on a two-component mixture consisting of a polymer with thermally labile bonds in its main-chain and a substance which can generate acid by exposure to radiation (e.g. triarylsulfonium salts [11]). Typical examples of the types of reactive polycarbonates we have prepared are polymers I, II, and III which are shown on page 141. 

On the basis of this analysis, we decided to develop new weakly coordinating anions that will be associated with various diaryliodonium salts, triarylsulfonium salts and ferrocenium salts... 

In this paper, we would like to report some recent work which has led to the development of triarylsulfonium salts (III) as a third class of useful photoinitiators for cationic polymerization and in particular, describe their application to the polymerization of epoxides. 

In our laboratory, we have found that triarylsulfonium salts (III) in which the anions are of the type BF , AsFg , PFg , SbFg , etc., are excellent photoinitiators for the polymerization of epoxy resins as well as a variety of other monomers (12, 13). Similar results have also been reported by another group of investigators (14). 

Triarylsulfonium salts may be conveniently prepared via a number of synthetic routes. In equations 2, 3 and 4 are shown three of the most direct preparative methods. 

Using the above synthesis, a wide variety of triarylsulfonium salt photoinitiators can be prepared. In Table 1 are shown some representative triarylsulfonium salt photoinitiators which were prepared during the course of this research. All the compounds in this table are well characterized crystalline compounds with well defined melting points, elemental analyses, ultraviolet, proton, and nmr spectra (T7). The ability of triarylsulfonium salts bearing non-nucleophilic counterions to serve as photoinitiators is completely general and includes all the symmetrical, unsymmetrical, substituted and unsubstituted as well as polynuclear and heterocyclic salts shown in Table 1. 

Although triarylsulfonium salts are highly thermally stable, they undergo rapid photolysis when irradiated at wavelengths from 200-300nm. Under these conditions, efficient ( 313,360 " 0.17-0.19) homolytic rupture of one of the carbon sulfur bonds results. The following mechanism has been proposed for this photolysis (12). 

Materials. Cyclohexene oxide and styrene oxide were dried over calcium hydride, then purified by fractional distillation. 3,4-Epoxycyclohexylmethyl-3, 4 -epoxycyclohexane carboxylate (ERL 4221) was obtained from the Union Carbide Company and purified as described above. Triarylsulfonium salts used as photoinitiators... 

On the other hand, it has been reported that triarylsulfonium salts are very reactive photoinitiators for the ring opening of epoxy monomers 7J. It was also reported (49) that a coating composed of 4% by weight of triphenylsulfonium hexafluorophosphate in 3,4-epoxy cyclohexyl methyl-3,4-epoxy cyclohexane carboxylate cured in 20 seconds exposure. 

Photochemistry of Triarylsulfonium Salts. A similar mechanism was proposed for the photolysis of triarylsulfonium salts having nonnucleophilic anions. The arylsulfonium and to a lesser extent, the aryliodonium salts have improved thermal stability as compared to the diazonium salts, however, their absorption maximum occurs at a much shorter wavelength since the aromatic rings are isolated by the heteroatom, and therefore not conjugated. 

The reaction of triarylsulfonium salts or diarylsulfoxides with organolithium or Grignard reagents affords diaiylsulfide and biaryl coupling products. The formation of sulfuranes with four carfocm-sulfiir bonds has been postulated for a long time. In 1971, Sheppard reported the detection of tetrakis(penta-fluorophenyl)sulfurane by NMR at low temperature, as an unstable intermediate in the reactions of pentafluorophenyllithium with fluorosulfurane derivatives which afforded decafluorobiphenyl and bis(pentafluorophenyl)sulfide. ... 

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