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epoxy resin[ə′päk·sē ′rez·ən]
any of a number of oligomeric products obtained by the polycondensation of epichlorohydrin with polyhydric phenols, alcohols, polyamines, or polybasic acids or by the epoxidation of compounds containing at least two double bonds.
The most widely used epoxy resins have the structural formula
These resins are obtained by reacting bisphenol A (diphenylol-propane) with epichlorohydrin in the presence of a base. The process has several stages, including polycondensation at 60°–100°C, rinsing with water to remove NaCl, and vacuum drying (13.3–26.6 kilo-newtons/m2) at 120°-140oC. The molecular weight of the resins depends on the ratio of the reagents used. The resins may be prepared in the form of viscous yellow liquids (molecular weight, 350–750; soluble in acetone and toluene) or yellow or brown solids (molecular weight, 800–3,500; soluble in a mixture of toluene and butanol).
Depending on the curing agent used, epoxy resins may be cured (hardened) at either elevated temperatures (60°–180°C), ambient temperatures, or lowered temperatures (as low as –15°C). Curing agents include polyamines, polybasic acids and their anhydrides, and polyhydric phenols, as well as tertiary amines and BF3 complexes. Upon curing, epoxy resins, unlike many other polymers, show little shrinkage (between 0.1 percent and 3 percent) and do not liberate volatile products.
Cured epoxy resins feature good adhesion to such materials as metals, glass, and concrete; they are also distinguished by their mechanical strength, chemical stability, heat resistance, water resistance, and good dielectric characteristics. The physicomechanical and technological properties of compositions that are based on epoxy resins vary widely and may be regulated by combining the resins with various monomers and polymers, as well as organic or mineral fillers. Epoxy resins are used as a base for high-strength binders and adhesives, hermetic sealers, varnishes, foam plastics, and electrical insulation compounds (seePOLYMER COMPOUNDS).
REFERENCESEntsiklopediia polimerov, vol. 3. Moscow, 1977.
Lee, H., and K. Neville. Spravochnoe rukovodstvo po epoksidnym smolam. Moscow, 1973. (Translated from English.)
E. M. BLIAKHMAN