Shrinkage during polymerization of epoxy resins is extremely low. These polyfunctional resins offer higher thermal properties and improved chemical resistance over bis-A derivatives. The cycloaliphatics comprise a third group of epoxy resins that are particularly important for applications requiring resistance to arc tracking and weathering. A fourth class of epoxy resins is based on the epoxidation of aromatic amines. These resins have good mechanical properties and high thermal capabilities and fatigue resistance.
Epoxies have excellent electrical, thermal, and chemical resistance.
Their strength can be further increased with fibrous reinforcement or mineral fillers. The variety of combinations of epoxy resins and reinforcements provides a wide latitude in properties obtainable in molded parts. Molded epoxy parts are hard, rigid, relatively brittle, and have excellent dimensional stability over a broad temperature range. Their excellent electrical properties, in combination with high mechanical strength, qualify them for electrostructural applications. Resins based on bisphenol-A are adequate for most services.