Synthetic resin is an industrially produced, typically viscous substance that converts into rigid polymers by the process of curing. They are formed by the reaction of dibasic organic acids and polyhydric alcohols. In order to undergo curing, resins typically contain reactive groups, such as acrylates or epoxides. Some synthetic resins have properties similar to natural plant resins, but many do not.
Synthetic resins are of several classes. Some are manufactured by esterification of organic compounds. Some are thermosetting plastics in which the term "resin" is loosely applied to the reactant(s), the product, or both. "Resin" may be applied to one or more monomers in a copolymer, the other being called a "hardener", as in epoxy resins. For thermosetting plastics that require only one monomer, the monomer compound is the "resin". For example, liquid methyl methacrylate is often called the "resin" or "casting resin" while in the liquid state, before it polymerizes and "sets". After setting, the resulting poly(methyl methacrylate) (PMMA) is often renamed "acrylic glass" or "acrylic". (Trade names include Plexiglas and Lucite).
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