Acylphosphinates

Phenacyl radicals are produced by photodecomposition of initiators containing the phenone moiety (Scheme 3.74). These initiators include benzoin derivatives and acylphosphine oxides (see 3.3.4.1.1). Acyl radicals can be formed by... 

Materials. The radical-type photopolymerizable formulation consisted of a mixture of hexanediol diacrylate (HDDA from UCB) and a polyurethane-diacrylate (Actilane 20 from Arkros). A bis-acylphosphine oxide (BAPO from Ciba) was used as photoinitiator at a typical concentration of 1 wt %. The cationic type photopolymerizable resin consisted of a mixture of the divinylether of triethyleneglycol (RapiCure DVE-3 from ISP) and a divinylether derivative of bis-phenol A (DVE-BPA). The cationic photoinitiator (Cyracure UVI-6990 from Union Carbide) had a composition of 50 wt % of mixed triarylsulfonium hexafluorophosphate salts and 50 wt % of propylene carbonate. The BAPO initiator... 

Goerlich, J.R., Mueller, C., and Schmutzler, R., Contributions to the chemistry of acylphosphines 1-adamantylacyl-, di-l-adamantylacyl- and 1-adaman-toylphosphines. Preparations and some reactions, Phosph., Sulf., Silic. Relat. Elem., 85, 193, 1993. 

The heterocyclic acylphosphines (52) and (53) have been prepared by the reaction of phenylbis(trimethylsilyl)phosphine with the acid chlorides derived from phthalic and diphenic acids. The reaction of 2,3-dichloromaleic anhydride or thioanhydride with phenylbis(trimethylsilyl)phosphine gives derivatives of the 1,4-dihydro-p-diphosphorin system (54).45... 

The chromophore in this type of photoinitiator is frequently an aromatic carbonyl. The benzoyl radical is the major initiating species, while the other fragment may also contribute to the initiation, in some cases. The most efficient type I initiators are benzoin ether derivatives, benzil ketals, hydroxyl-alkylphenones, a-aminoketones, and acylphosphine oxides. Substituents on the aromatic carbonyl influence the absorption. 

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... 

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. 

The silyl migration method involves intramolecular 1,3-silyl migration which is useful for introducing phosphorus multiple bonds. Variations of this 1,3-silyl migration have been classified as the condensation-silatropy method and the addition-silatropy method (Scheme 3)8. Becker reported a reaction involving rearrangement of silyl-substituted acylphosphine for the first time in 1976 (equation 3)9. 

Alkyl ethers of benzoin Benzil dimethyl ketal 2-Hydroxy-2-methylphenol-l-propanone 2,2-Diethoxyacetophenone 2-Benzyl-2-At, V-dimethylamino- l-(4-morpholinophenyl) butanone Halogenated acetophenone derivatives Sulfonyl chlorides of aromatic compounds Acylphosphine oxides and bis-acyl phosphine oxides Benzimidazoles... 

Free radical promoted, cationic polymerization also occurs upon irradiation of pyridinium salts in the presence of acylphosphine oxides. But phosphonyl radicals formed are not oxidized even by much stronger oxidants such as iodonium ions as was demonstrated by laser flash photolysis studies [51, 52]. The electron donor radical generating process involves either hydrogen abstraction or the addition of phosphorus centered or benzoyl radicals to vinyl ether monomers [53]. Typical reactions for the photoinitiated cationic polymerization of butyl vinyl ether by using acylphosphine oxide-pyridinium salt combination are shown in Scheme 10. 

Quite a dilferent reaction of acetyldiphenylphosphine (4) is responsible for the formation of the oxide (5) from acetic acid and chlorodiphenylphosphine. The phosphine (4) is shown (Scheme 1) to be an intermediate in the reaction, and to undergo an unexpected addition of acetic acid to form (5). The involvement of an acylphosphine is the essential difference between the reactions of chlorodiphenylphosphine with acetic acid and with trifluoroacetic acid the latter produces (3). ... 

Electron.—Electron diffraction has shown that the acylphosphine (172) has larger bond angles than trimethylphosphine. Chloromethylphosphonyl dichloride (173 ... 

Inversion, Non-equivalence, and Configuration.— Lowering of the inversion barrier of the acylphosphine (49) by conjugation of the phosphorus lone pair of electrons with the carbonyl group was confirmed by the sensitivity of inversion to the nature of Non-equivalence of the apical fluorine atoms in... 

Some cures can even be done in sunlight in 2 min using the acylphosphine initiator (8.52).310... 

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