J. Pascault, Roberto J. J. Williams
Mar 9, 2010
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Abstract
The most popular epoxy monomers are those derived from the reaction of bis(4 hydroxy phenylene) 2,2 propane (called bisphenol A) and 1 chloroprene 2 oxide (called epichlorohydrin), in the presence of sodium hydroxide. The structure of the major product, bisphenol A diglycidyl ether (DGEBA or BADGE) and its condensed forms (Table 1.1 a), is dependent upon the stoichiometry of the reactants. Typical monomers ( “ resins ” ) are marketed with n values lying in the range 0.03 – 10. At room temperature these monomers are crystalline solids for n values close to zero, liquids for n values up to n = 0.5, and amorphous solids (glass transition temperature, T g ∼ 40 – 90 ° C) for higher n values. Another major group of epoxy monomers derived from epichlorohydrin is that comprising monomers synthesized with an aromatic amine, such as methylene dianiline (TGMDA) (Table 1.1 b). Oxirane groups can be generated by peroxidation of carbon – carbon double bonds. Types of such oligomers are epoxidized oils or cycloaliphatic oxides (Table 1.1 c). Epoxy monomers containing vinyl groups, like glycidyl (meth)acrylate or glycidyl oxystyrene (Table 1.1 d), can be used for the synthesis of functional oligomers. Linear or crosslinked epoxy polymers are obtained by reaction of the epoxy monomers with co monomers ( “ hardeners ” ) and/or initiators. Epoxy polymers can be produced by step or chain polymerizations or, eventually, by a combination of both mechanisms. Step growth polymerization proceeds via a step by step succession of elementary reactions between reactive sites. Each independent step causes the disappearance of two co reacting sites and creates a new covalent bond between a pair of functional groups. The number of reactive sites per monomer (functionality) and the molar ratio between co reactive sites are the main parameters that control the 1