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Sensitization of Cationic Photopolymerizations

Dyes and Chromophores in Polymer Science, Fii t Edition. Edited by Jacques Lalevee and Jean-Pierre Fouassier. ISTE Ltd 2015. Published by ISTE Ltd and John Wiley Sons, Inc. [Pg.45]


NVK is used as a sensitizer of cationic photopolymerization. Cation-ically photopolymerizahle, or photocurable, compositions typically contain monomers or oligomers having the epoxy or the ether functionality, and a photoinitiator. The most commonly used photoinitiators employed for photoinduced cationic ring-opening pol5mierizations are diaryliodon-ium salts, or triarylsulfonium salts. [Pg.13]

Photopolymerization reactions are widely used for printing and photoresist appHcations (55). Spectral sensitization of cationic polymerization has utilized electron transfer from heteroaromatics, ketones, or dyes to initiators like iodonium or sulfonium salts (60). However, sensitized free-radical polymerization has been the main technology of choice (55). Spectral sensitizers over the wavelength region 300—700 nm are effective. AcryUc monomer polymerization, for example, is sensitized by xanthene, thiazine, acridine, cyanine, and merocyanine dyes. The required free-radical formation via these dyes may be achieved by hydrogen atom-transfer, electron-transfer, or exciplex formation with other initiator components of the photopolymer system. [Pg.436]

Sensitization Via Exciplexes The use of photosensitizers is critical to the success of cationic photopolymerizations in many applications in which photopolymerizations are employed as it accelerates the rates of reactions and requires less energy as they provide polymerizations in longer wavelengths [106],... [Pg.446]

The reversibility of proton transfer limits to some extent the nature of the monomers which are subject to photopolymerization with these initiator systems, but epoxides, trioxane and vinyl ethers work very well (12,14). The sensitization of cationic polymerizations photoinitiated by compounds II and III has been reported by Crivello and Lee (13). [Pg.434]

The first reaction describes the excitation of uranyl ions. The excited sensitizer can lose the energy A by a non-radiative process (12b), by emission (12c) or by energy transfer in monomer excitation to the triplet state (12d). Radicals are formed by reaction (12e). The detailed mechanism of step (12e) is so far unknown. Electron transfer probably occurs, with radical cation and radical anion formation these can recombine by their oppositely charged ends. The products retain their radical character. Step (12g) corresponds to propagation and step (12f) to inactivation of the excited monomer by collision with another molecule. The photosensitized initiation and polymerization of methacrylamide [69] probably proceeds according to scheme (12). Ascorbic acid and /7-carotene act as sensitizers of isoprene photoinitiation in aqueous media [70], and diacetyl (2, 3-butenedione) as sensitizer of viny-lidene chloride photopolymerization in a homogeneous medium (N--methylpyrrolidone was used as solvent) [71]. [Pg.89]

TOB 99] Toba Y., Saito M., Usui Y., Cationic photopolymerization of epoxides by direct and sensitized photolysis of onium tetiakis(pentafluoropheityl)borate irniiaXors , Macromolecules, vol. 32, no. 10, pp. 3209-3215, 1999. [Pg.78]

Derivatives of anthracene and carbazole are typical electron-transfer photosensitizers. Of practical interest are derivatives containing cationically polymerizable epoxide groups (see Chart 10.5) [54]. During the ring-opening photopolymerization of epoxides, these sensitizers are covalently incorporated into the polymeric network and cannot be removed by extraction. Therefore, the potential risk of toxic effects of the sensitizers is strongly diminished. [Pg.292]

Oxman et al., smdied controlled, sequentially curable cationic/free radical hybrid photopolymerization of diepoxide/acrylate hybrid material with the aid of photodifferential scanning calorimetry. The polymerizations were carried out in the presence of various concentrations of either ethyl-4-dimethylamino benzoate or 4-tert-butyl-N,N,-dimethylaniline as electron donors and camphoquinone/diphenyliodonium hexafluoroantimonate as the sensitizing system. The results showed that the free-radical acrylate reactions always precede the cationic epoxy polymerizations. [Pg.178]

Gregory patented Ultraviolet Curable Resin Compositions Having Enhanced Shadow Curing Properties in 2001. This patent has the same idea as Dixon s patent, that is, use photopolymerization at the surface of a filled resin to trigger a thermal front. Gregory went beyond using peroxide-cured vinyl resins. He used dialkyl iodonium salts, sensitized by a-hydroxy ketones, that produced Lewis acids upon UV irradiation. The Lewis acid triggered cationic polymerization of epoxy resins and vinyl ethers. The heat from the photoinitiated process decomposes peroxides into radicals that react with the iodonium salts to produce Lewis acids. [Pg.975]

Modification of electrode surfaces with polymer is seeking the same objective as with monolayers, i.e., the improvement of the analytical performances in terms of selectivity and sensitivity. These improved performances can be achieved by the nature of the polymer itself (e.g., perfluorinated cation-exchanger Nafion ) or by the incorporation of chemical functionalities. Recognition elements (e.g., biomolecules, ligands) can be entrapped during the polymerization process (electro- or photopolymerization) or attached after polymerization by chemical grafting or by... [Pg.434]


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