Patents photoinitiators

Although phosphine [7803-51-2] was discovered over 200 years ago ia 1783 by the French chemist Gingembre, derivatives of this toxic and pyrophoric gas were not manufactured on an industrial scale until the mid- to late 1970s. Commercial production was only possible after the development of practical, economic processes for phosphine manufacture which were patented in 1961 (1) and 1962 (2). This article describes both of these processes briefly but more focus is given to the preparation of a number of novel phosphine derivatives used in a wide variety of important commercial appHcations, for example, as flame retardants (qv), flotation collectors, biocides, solvent extraction reagents, phase-transfer catalysts, and uv photoinitiators. 

Janke, C.J., Lopata, V.J., Havens, S.J., Dorsey, G.F. and Moulton, R.J., High energy electron beam curing of epoxy resin systems incorporating cationic photoinitiators, US Patent 5,877,229, 1999. 

On-aircraft repairs of composite using a rapid-cure resin system of composite component with UV light irradiation based on TRI patenP have been developed by the U.S. Air Force Research Laboratory. Alternating layers of the acrylate-based resin system and woven fiberglass (the widely used wet la)mp procedure) are applied to fill the hole and form a UV curable composition. The width of the patch can be up to 2 ft (0.6 m) and the depth as much as 0.2 in. (5 mm). The cure time using a 400 W UVA lamp is reported to be 20 min. Although it is essentially a depot repair, it can be done field when necessary to return an aircraft to service. Because of the necessity to cure relatively thick repair patches, Us-acylphosphine oxide was used as a photoinitiator. An example of the patented UV curable resin system used for the repairs is in Table 11.1. 

Sulfinates. Arylsulfinate anions were shown to be effective activators for photoreducible dye polymerization systems by Hiller, Margerum, and Rust (41). The work is described with applications in a number of patent publications (20,41a,42). These workers also studied the mechanism of the photoinitiation process (43). 

A considerable number of detailed descriptions on synthesis, production, and applications of epoxy resins exists. Because the aim of this chapter is the application of cationic initiators, and more particularly photoinitiators, to the polymerization of epoxies leading to cross-linked products (curing reaction), only litterature dealing with these aspects will be cited. For the general aspects of epoxy resins the scientific and patent literature may be found in detailed reviews [119,120] and classical books [121-123]. 

There are numerous references in the Patent Literature (72—76) to the use of anthraquinone and similar compounds as photoinitiators of polymerization or crosslinking required in the preparation of printing plates etc, although apparently little is known of the detailed reaction mechanisms. One literature report (77) described the polymerization of aqueous methyl acrylate by sodium anthraquinone-2-sulphonate in the presence of chloride ions, with a conclusion that the initiating species are chlorine atoms. 

Polymeric systems containing side-chain benzoin moieties, recently appearing [100,102] in the patent literature, have been applied as photoinitiators to UV curing of prepolymers of a different nature. In particular, siloxane-compatible photocrosslinking initiators (PSBME) are manufactured [100] by reacting silox-anes with benzoin ether derivatives (Scheme 23) and used in UV curing of acryloxypropyl-terminated dimethylsiloxane prepolymers. 

Diaryliodonium Salts. The use of diaryliodonium salts as photoinitiators for epoxide polymerization was first described in Belgian Patents issued in 1975 and 1976 (, ). Diaryl-... 

Iodonium Salts. Recent developments in the synthesis of iodonium salts useful in photoinitiated polymerization processes have been driven primarily by the desire for increased solubility of the salts in the polymerization media. Metathesis of diaryliodonium bisulfate to diaryliodonium tetrafluoroborate was patented by Klemm and Bartin [27] in 1986,... 

Compositions having, upon polymerization, good adhesion and sealing properties were described by Nippon Soda [137] in 1986. The composition comprised an epoxidized polybutadiene, epoxy resin, onium salt, and sensitizer. Grace Japan [138] patented the simultaneous photopolymeriza-tion of epoxy compounds and compounds containing unsaturated groups by the use of free radical photoinitiators and sulfonium salts in 1986. 

In 1987, UVEXS [145] claimed simultaneous cationic and free radical polymerization of a mixture of a cycloaliphatic epoxy resin, a hydroxy functional polyether terminated polysiloxane, an acrylate functional resin, a triarylsulfonium salt, and a free radical photoinitiator. A simultaneously cured cationically and free radically polymerized system consisting of an epoxy resin, a methacrylate monomer, an onium salt, a carbonyl type free radical photoinitiator, and tetrahydrofurfuryl alcohol accelerator was patented by Cook Paint and Varnish [146] in 1987. 

Interest continues in the use of transition-metal co-ordination complexes, e.g. VO(acac)2Cl, as photoinitiators for vinyl polymerization. Note that the patent literature relating to photopolymerization is covered in Appendix Al. 

Ito and C.G. Willson, Chemical amplification in the design of dry developing resist materials, Polym. Eng. Sci. 23, 1012 (1983) H. Ito, C.G. Willson, and J.M.J. Frechet, Positive and negative working resist compositions with acid generating photoinitiator and pol3mier with acid labile groups pendant from polymer backbone, U.S. Patent No. 4,491,628 (1985). 

Normally, a small amount of photoinitiator is required to cure UV systems efficiently. Several patents have described the use of specially prepared monomers or polymers which contain built-in photoinitiators. 

Many recent publications and patents give evidence of the growing interest in photoinitiated cationic polymeri-... 

A patent was issued to BASF that describes two component photoinitiators containing mono- or a diacylphosphine oxide, which is described as R1R2P(0)C(0)R3. The other component is mono or polysubsituted benzophenone. These photoinitiators are low in volatility. It is claimed that they are not inhibited by air and are particularly suitable for ultraviolet light curing of coatings. 

It is interesting to note that a reeent patent deseribes a light eurable coating composition that includes eationie photoinitiator and/or free radieal photoinitiator, in combination with a charge transfer eomplex. The eharge transfer complex is described as an singlet eleetron withdrawing reaetant component... 

Two patents were applied for by Baudin and Jung, for use of three compounds shown below, and similar ones, as photoinitiators that accumulate at the surface of the formulation and ensure surface cures ... 

The patent states that photoinitiators composed of quinolinum salts (N-benzylquinolinium hexachloro-antimonate) and sulfonium salts like the one shown above show a maximum molecular extinction coefficient greater that 100 at 360 to 500 nm. ... 

Development of new sulfonium salts was patented by Herlihy. These materials are claimed to be useful as photoinitiators for surface coatings, printing inks and varnishes. They were illustrated in two ways as is shown on the next page. In the first illustration Ri = 0,CH2, S,C=0,(CH2)2, NH, N-alkyl R4.7 = H Rg.ii = H, Hydroxy, or alkyl or Rg and Rn form a fused ring system with the benzene rinds to which they are attached. R12 that can be a direct bond or it can be an O or a CH2. 

Also, a European patent was applied for that describes cationic photoinitiators based on 2,4,6-triarylpyrylium salts with nonnucleophilic anions and electron donors. It is claimed that the photoinitiators rapidly photo crosslink mixtures of cycloaliphatic epoxides. Micro encapsulation of the salts in polystyrene was found to increase thermal and photo stability of these photoinitiators.The encapsulation material can be dissolved in monomers when polymerization is desired. 

A Japanese patent reports phosphine oxide sulfonium borate salts as photoinitiators. The compounds show good storage stability and compatibility. The materials are illustrated below. Both boron salts shown in the illustration are claimed to be effective in initiating either free radical and cationic polymerizations ... 

Hagemeyer, A. and Kuhlein, K., Photoinitiation of sulfochloration or sulfoxidation of alkanes using UV-excimer radiation for the manufacture of alkylsulfonyl chlorides and aUcylsulfonates, European Patent Application EP 1,028,107, 2000. 

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