Acrylates reaction with radicals

In general, acryUc ester monomers copolymerize readily with each other or with most other types of vinyl monomers by free-radical processes. The relative ease of copolymerization for 1 1 mixtures of acrylate monomers with other common monomers is presented in Table 7. Values above 25 indicate that good copolymerization is expected. Low values can often be offset by a suitable adjustment in the proportion of comonomers or in the method of their introduction into the polymerization reaction (86). 

Tabic 1.3 Relative Rate Constants for Reactions of Radicals with Alkyl-Substituted Acrylate Esters CHR CFEcOaCHs"... 

Outcomes from the reactions of radicals with substituted acrylate esters depend on the attacking radical (refer Table 1.3 and Scheme 1.4). The results may be summarized as follows (the methyl substituent is usually considered to be electron donating - Section 1.2.2) ... 

Transition metal salts trap carbon-centered radicals by electron transfer or by ligand transfer. These reagents often show high specificity for reaction with specific radicals and the rates of trapping may be correlated with the nucleophilicity of the radical (Table 5.6). For example, PS radicals are much more reactive towards ferric chloride than acrylic propagating species."07... 

The use of metal-complex initiating systems proved to be especially promising in carrying out the reactions with acrylic monomers which can be easily polymerized, when the common initiators of radical reactions are excepted. The use of Fe(CO)s -I- DMFA system allows us to perform homolytical addition of bromoform to acrylic monomers selectively at C-Br bond with no essential polymerization (ref. 10). 

A radical cyclization of a 2-chloroacyl enamine 157 was used to synthesize 2-substituted pyroglutamates 160. Usually, the radical 158 undergoes an initial 5-endo cyclization (path a) and the resulting intermediate 159 attacked electrophiles like methyl acrylate to give the pyroglutamate 160. Unexpectedly, the reaction with methyl methacrylate took another course and a seven-membered... 

There have also been several papers [61-63] on the importance of carefully establishing the reaction mechanism when attempting the copolymerization of olefins with polar monomers since many transition metal complexes can spawn active free radical species, especially in the presence of traces of moisture. The minimum controls that need to be carried out are to run the copolymerization in the presence of various radical traps (but this is not always sufficient) to attempt to exclude free radical pathways, and secondly to apply solvent extraction techniques to the polymer formed to determine if it is truly a copolymer or a blend of different polymers and copolymers. Indeed, even in the Drent paper [48], buried in the supplementary material, is described how the true transition metal-catalyzed random copolymer had to be freed of acrylate homopolymer (free radical-derived) by solvent extraction prior to analysis. 

Radical cyclization to macrolides.111 Cyclization of iodoalkyl acrylates (1) by reaction with Bu3SnH (1 equiv.) in the presence of AIBN is useful for formation of macrolides (2) containing 11 or more members. Similar cyclization of iodoalkyl fumarates (3) results in two macrolides with the endo-product predominating except when n is 16 or higher. Tertiary iodides undergo this free radical cyclization more... 

Free radical A reactive species having an unpaired electron that initiates a reaction with a double bond, for example, in acrylate polymerization. It is produced from its stable paired state by energy absorption. 

The simple addition reaction in Scheme 19 illustrates how the notation is used. Ester (1) can be dissected into synthons (2), (3) and (4). Synthons for radical precursors (pro-radicals) possess radical sites ( ) A reagent that is an appropriate radical precursor for the cyclohexyl radical, such as cyclohexyl iodide, is the actual equivalent of synthon (2). By nature, alkene acceptors have one site that reacts with a radical ( ) and one adjacent radical site ( ) that is created upon addition of a radical. Ethyl acrylate is a reagent that is equivalent to synthon (3). Atom or group donors are represented as sites that react with radicals ( ) Tributyltin hydride is a reagent equivalent of (4). In practice, such analysis will usually focus on carbon-carbon bond forming reactions and the atom transfer step may be omitted in the notation for simplicity. 

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