Epoxide rings, acrylation

For this use, the preferred powders are based on acrylic, epoxy or polyester and epoxy resins. For best colour, epoxy resins are crosslinked with anhydrides of dicarboxylic acids in the straight epoxy coatings, or with saturated polyesters of high acid content in the epoxy-polyester type. Acrylics contain epoxide rings via, for example, glycidyl methacrylate (CH2=C(CH3) —CO—O—CHj—CH —CH2), and these groups crosslink... 

It turns out that it is difficult to use the ketone to control the stereochemistry of the epoxidation. If acrylic acid is used as the dienophile, bromolactonisation of the product 67 gives a mixture of five- 68 and six-membered 69 lactones in 86% yield and a 1 1.5 ratio. Fortunately, treatment of both with an alkyl-lithium makes the same epoxide 70 by ring opening and Sn2 closure of the epoxide.8 The reaction works well only with an electron-withdrawing group X such as SPh that must be removed later. Addition of MeLi to the ketone and elimination gives 62. 

Thus this type of epoxy resin contains a maximum of two epoxide rings at the ends of the molecule and a number (which may be zero) of hydroxyl groups along the chain. These groups make the resin a polar one and ensure good adhesion to polar or metallic surfaces. The next thing to note is that the polymer chain contains only carbon-carbon and ether linkages. Both are very stable. We have seen the C-C stability in acrylic polymers, and in the preparation of nitrocellulose... 

Vinyl ester resins are produced by the addition of ethylenically unsaturated carbo acids (methacrylic or acrylic acid) to an epoxide resin (usually of the bisphenol epichlorohydrin type). The reaction of acid addition to the epoxide ring (esterification exothermic and produces a hydroxyl group without the formation of by-products. Appropriate diluents and polymerization inhibitors are added during or after esterification. 

Negative photoresist chemistry. A. Cross-linking of a prolyisoprene rubber by a photoreactive bisazide. B. A radical induced polymerization and cross-linking of an acrylate monomer. C. A single component resist. Electron beam irradiation produces anions that launch a cascade of epoxide ring-opening reactions to cross-link the poljrmer. 

Other means to introduce polymerizable groups on the fatty acids is the acrylation of the epoxide rings (Fig. 22.21) [4,103], hi this sense, the reaction of epoxidized fatty acids with acrylic acid incorporates acrylate groups on the fatty acid structure. Next, the monomers produced can be copolymerized with styrene using a free radical initiator to produce cross-linked materials. 

For the construction of the I ring, the vinylic group introduced to activate the y-hydroxy epoxide moiety of 28 towards cyclization is an acrylic ester residue, which concomitantly allows cyclization on the allylic position, with formation of the tricyclic compound 29 containing the IJK fragment of the natural product, and fur-... 

Another immobilized system was recently reported by Wei and Liu [64] using amphiphilic coblock polymers consistent of ethylene glycol and methyl acrylate monomers that had been functionalized with imidazole groups. In combination with oxone (KHS05) as the oxidant in an ethyl acetate/water mixture, this system yields the 1,2-diol product in 62% yield, which is probably formed by ring opening of the epoxide by the acidic oxone. 

The reductive cyclization of epoxides with alkenes and alkynes provides a very useful method for the synthesis of complex carbocyclic ring systems. Several interesting applications of this methodology have been reported in the past year. Two examples report the cyclization of an epoxide with an acrylate as the terminating group <07T 11341 ... 

An intermolecular iron-catalyzed ring expansion reaction involving epoxides and alkenes provided tetrahydrofurans via radical processes <07CEJ4312>. Cp2TiCl is able to promote cyclization of 2,3-epoxy alcohols containing a p-(alkoxy)acrylate moiety to form tetrahydrofurans <07TL6389>. As shown in the following example, an intramolecular addition of carbon radicals to aldehydes was reported to afford tetrahydrofuran-3-ols... 

The most important limitation related to commercial applications is relatively low reactivity of epoxide-based resins, commonly used in coatings, compared to acrylate based systems. Therefore, most works have been effort to accelerate ring-opening polymerization of epoxides. There are four different strategies to speed up the polymerization ... 

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