In chemistry, a trimer is a product derived from three identical precursors. Trimers are typically cyclic. Chemical compounds that often trimerise are aliphatic isocyanates and cyanic acids. Often, trimerization competes with polymerization.
In the Reppe synthesis, the trimerization of acetylene gives benzene:
Another example is the procedure of production of polymers. At first, a monomer is made. By combining two monomers, a dimer is produced. With further additions, a trimer and eventually a polymer is made.