What is "synthetic resin"

n. a resin having a polymeric structure; especially a resin in the raw state; used chiefly in plastics

Synthetic resins are materials with a property of interest that is similar to natural plant resins: they are viscous liquids that are capable of hardening permanently. Otherwise, chemically they are very different from the various resinous compounds secreted by plants (see resin for discussion of the natural products).

The synthetics are of several classes. Some are manufactured by esterification or soaping of organic compounds. Some are thermosetting plastics in which the term "resin" is loosely applied to the reactant or product, or both. "Resin" may be applied to one of two 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 it is in the liquid state, before it polymerizes and "sets". After setting, the resulting PMMA is often renamed acrylic glass, or "acrylic". (This is the same material called Plexiglas and Lucite).