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Photoinitiated carbonylations

In the i.r. spectrum of a material Ilia (12.9 wt % poly-DMAEMA on silica) the typical photoinitiator carbonyl absorption is present at 1642 cm (Figure 4). Such a material should tse still active toward undiluted DMAEMA and NVP if the photoinitiator group is accessible to the applied nranomer. The corresponding photopolymerization experiments provided the materials Ilia and IIIa A - With DMAEMA the polymer content was increased to 32.6 wt % poly-DMAEMA (Ilia) and NVP led to a composite Illa /b with 27.7 wt % poly-NVP. [Pg.119]

Unfortunately, the use of palladiiun(0)-catalyzed carbonylation reactions in carbon-11 chemistry is restricted by problems related to the competing /3-hydride elimination for electrophiles bearing a hydrogen in the j8-position. In order to overcome this restriction, uncatalyzed photoinitiated carbonylation reactions have been more closely investigated using alkyl iodides, amines and alcohols as precursors. The first results were promising, providing esters and amides in the majority of cases in radiochemical yields of 40-70% as indicated for the examples 50-55 ... [Pg.228]

Figure 5.21 Use of photoinitiated carbonylations in the synthesis of carbon-11-labeled aliphatic esters and amide... Figure 5.21 Use of photoinitiated carbonylations in the synthesis of carbon-11-labeled aliphatic esters and amide...
The end group of the polymers, photoinitiated with aromatic amine with or without the presence of carbonyl compound BP, has been detected with absorption spectrophotometry and fluororescence spectrophotometry [90]. The spectra showed the presence of tertiary amino end group in the polymers initiated with secondary amine such as NMA and the presence of secondary amino end group in the polymers initiated with primary amine such as aniline. These results show that the amino radicals, formed through the deprotonation of the aminium radical in the active state of the exciplex from the primary or secondary aromatic amine molecule, are responsible for the initiation of the polymerization. [Pg.239]

The photoinitiation of vinyl polymerization by organic compounds (carbonyl, azo, peroxide, disulphide compounds, etc.) or inorganic salts (e.g., metal halides and their ion pairs, etc.) will not be discussed here, since these type of photoinitiators are beyond the scope of the present chapter. [Pg.244]

Thus, a mixture of simple carbonyls Me(CO)n and halides should behave as a photoinitiator of free radical polymerization. Many such systems have been found to function in this way. Complexes formed by irradiation of Fe(CO)5 in the presence of a vinyl monomer (M) (such as MMA, styrene, vinyl acetate, propylene, and vinyl ether) have been studied by Koerner Von Grustrof and colleagues [12,13] and shown to have the chemical struc-... [Pg.245]

Strohmeier and Hartmann [14] first reported in 1964 the photoinitiation of polymerization of ethyl acrylate by several transition metal carbonyls in the presence of CCI4. Vinyl chloride has also been polymerized in a similar manner [15,16] No detailed photoinitiation mechanisms were discussed, but it seems most likely that photoinitiation proceeds by the route shown in reaction Scheme (9). [Pg.245]

Osmium carbonyl (Os3(CO)i2) acts as a photoinitiator of vinyl polymerization [20], which can function without a halide additive. The mechanism of photoinitiation is by a hydrogen abstraction from monomer to pho-... [Pg.246]

It has generally been concluded that the photoinitiation of polymerization by the transition metal carbonyls/ halide system may occur by three routes (1) electron transfer to an organic halide with rupture of C—Cl bond, (2) electron transfer to a strong-attracting monomer such as C2F4, probably with scission of-bond, and (3) halogen atom transfer from monomer molecule or solvent to a photoexcited metal carbonyl species. Of these, (1) is the most frequently encountered. [Pg.247]

It is clear from the preceding discussion that organometallic photoinitiators (metal carbonyl or chelate derivatives) can provide a convenient route for synthesizing vinyl polymers with a variety of different reactive end group or photoreactive pendant groups or side chains through the polymer chain. [Pg.253]

The block copolymer produced by Bamford s metal carbonyl/halide-terminated polymers photoinitiating systems are, therefore, more versatile than those based on anionic polymerization, since a wide range of monomers may be incorporated into the block. Although the mean block length is controllable through the parameters that normally determine the mean kinetic chain length in a free radical polymerization, the molecular weight distributions are, of course, much broader than with ionic polymerization and the polymers are, therefore, less well defined,... [Pg.254]

Hutchinson, J. and Ledwith, A. Photoinitiation of Vinyl Polymerization by Aromatic Carbonyl Compounds. Vol. 14, pp. 49 — 86. [Pg.154]

Many reviews have been written on the photochemistry of aromatic carbonyl compounds269 and on the use of these compounds as photoinitiators.270 272 Primary radicals are generated by one of the following processes ... [Pg.98]

Photochemically-generated radicals are encountered as reactive intermediates in many important systems, being a major driving force in the photochemistry of ozone in the upper atmosphere (stratosphere) and the polluted lower atmosphere (troposphere). The photochemistry of organic carbonyl compounds is dominated by radical chemistry (Chapter 9). Photoinitiators are used to form radicals used as intermediates in the chain growth and cross-linking of polymers involved in the production of electronic circuitry and in dental treatment. [Pg.128]

Explain the role of the photochemical reactions of carbonyl compounds in the photoinitiated polymerisation of vinyl monomers and cross-linking in polymers. [Pg.161]

Aryl methyl ketones have been obtained [4, 5] by a modification of the cobalt-catalysed procedure for the synthesis of aryl carboxylic acids (8.3.1). The cobalt tetracarbonyl anion is converted initially by iodomethane into the methyltetra-carbonyl cobalt complex, which reacts with the haloarene (Scheme 8.13). Carboxylic acids are generally obtained as by-products of the reaction and, in several cases, it is the carboxylic acid which predominates. Unlike the carbonylation of haloarenes to produce exclusively the carboxylic acids [6, 7], the reaction does not need photoinitiation. Replacement of the iodomethane with benzyl bromide leads to aryl benzyl ketones in low yield, e.g. 1-bromonaphthalene produces the benzyl ketone (15%), together with the 1-naphthoic acid (5%), phenylacetic acid (15%), 1,2-diphenylethane (15%), dibenzyl ketone (1%), and 56% unchanged starting material [4,5]. a-Bromomethyl ketones dimerize in the presence of cobalt octacarbonyl and... [Pg.387]

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. [Pg.67]

This reaction is based on a stoichiometric reaction of multifunctional olefins (enes) with thiols. The addition reaction can be initiated thermally, pho-tochemically, and by electron beam and radical or ionic mechanism. Thiyl radicals can be generated by the reaction of an excited carbonyl compound (usually in its triplet state) with a thiol or via radicals, such as benzoyl radicals from a type I photoinitiator, reacting with the thiol. The thiyl radicals add to olefins, and this is the basis of the polymerization process. The addition of a dithiol to a diolefin yields linear polymer, higher-functionality thiols and alkenes form cross-linked systems. [Pg.77]


See other pages where Photoinitiated carbonylations is mentioned: [Pg.431]    [Pg.245]    [Pg.245]    [Pg.246]    [Pg.247]    [Pg.254]    [Pg.599]    [Pg.74]    [Pg.79]    [Pg.201]    [Pg.210]    [Pg.82]    [Pg.151]    [Pg.66]    [Pg.76]    [Pg.65]    [Pg.74]   
See also in sourсe #XX -- [ Pg.228 ]




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Carbon photoinitiated carbonylations

Photoinitiated

Photoinitiation

Photoinitiator

Photoinitiators

Photoinitiators aromatic carbonyl compound

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