Epoxy resins synthesis reaction

Scheme 1.18. The reaction sequence for DGEBA-based epoxy-resin synthesis.

Figure 3.2 (a) Epoxy resin synthesis generalized reaction (b) reaction of hydroxyl group of NaOH with proton (c) displacement of the chlorine atom by the hydroxyl group (d) chain propagation (e) termination step. 

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Synthesis Epoxy resins consisting ofglycidyl ether, ester and amines are generally prepared by the condensation reaction between diol, dibasic acid or amine and epichlorohydrin in the presence of sodium hydroxide with the elimination of hydrochloric acid. The commercially available epoxy resins are, however, made by the reaction of epichlorohydrin and bisphenol-A. Cashew nut shell liquid (CNSL)-based novolac epoxy resins have also been reported [342]. 

Massing described a synthesis of systematically modified cationic lipids by solid-phase chemistry starting with the immobihsation of (/f)-2,3-epoxy-1 -propanol on 4-methoxytrityl chloride resin [157], Reaction of the epoxide with distinct long-chained amines was followed by reductive animation and tertiary amine quatemisation (see Fig. lib). This interesting method allowed the solid-phase coupling of three different lipophUic moieties on an amino group and the synthesis... 

Bisphenol A is manufactured by a reaction between phenol and acetone, the two products from the cumene hydroperoxide rearrangement. Bisphenol A is an important diol monomer used in the synthesis of polycarbonates and epoxy resins. 

Lin, C. H., Synthesis of novel phosphorus-containing cyanate esters and their curing reaction with epoxy resin, Polymer, 2004, 45, 7911-7926. 

As industrial relevant Friedel-Crafts reaction, the synthesis of Bisphenol-F, a material for epoxy resin, from phenol and formaldehyde was chosen [57]. This reaction involves formation of higher order condensates such as tris-phenols. To minimize the latter, the molar ratio of phenol to formaldehyde is set to a very high value (30-40), which is more than 15 times larger than the amount theoretically necessary. Three types of micromixers were used. These are a T-shaped mixer with 500 pm inner diameter, a multilaminating interdigital micromixer with 40 pm channels and a so-called self-made K-M micromixer with center collision mixing. 

Epoxy resin can have varying amounts of inorganic material remaining in the product after its synthesis. One of these is sodium chloride, which is formed by the reaction of sodium hydroxide with epichlorohydrin molecules, as described in Chap. 2. This is important in electrical applications because the sodium salt can be hydrolyzed and can degrade electrical properties. Some epoxy resin manufacturers will offer special ultrapure electrical grades or low-chlorine grades of epoxy resins for application where this is an important factor. 

Proper formulation of epoxy adhesives requires knowledge of the chemical reactions that lead to polymerization as well as the chemical and physical properties of both the uncured mixture and the cured material. This chapter reviews the general principles of epoxy resin chemistry including synthesis of the epoxy monomer itself and its possible polymerization reactions. 

The ratio of the main ingredients used in the synthesis of epoxy resins (epichlorohydrin bisphenol A) determines the extent of the reaction and the molecular weight (or value of n repeating units in the molecular chain). The addition of bisphenol A to the reaction mix will advance the molecular weight of the resin and the value of n. As n increases, the viscosity or melting point of the resin also increases. Also as the value of n increases, the number of hydroxyl groups increases while the number of epoxy groups remains constant. 

A considerable number of detailed descriptions on synthesis, production, and applications of epoxy resins exists. Because the aim of this chapter is the application of cationic initiators, and more particularly photoinitiators, to the polymerization of epoxies leading to cross-linked products (curing reaction), only litterature dealing with these aspects will be cited. For the general aspects of epoxy resins the scientific and patent literature may be found in detailed reviews [119,120] and classical books [121-123]. 

Finally, the Mannich reaction may be applied to the. synthesis of reactive amines used as crosslinking agents of epoxy resins. The process requires the availability of molecules possessing more than two NH groups, which are obtained by reaction of polyfunctional substrates with polyfunctional primary amines (oligomeric polyalkyle-ncamines, diamino cyclohexane, etc.) - (see also 422, Chap. Ill, C). 

Similarly, in the preparation of low molecular weight analogue, bis-phenol F, preferential reaction to form para-para links is achieved using acid catalysis. Bis-phenol F is an important intermediate in the synthesis of epoxy resins (see Section IV.B). 

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