High Quality Content by WIKIPEDIA articles! High Quality Content by WIKIPEDIA articles! In chemistry a trimer is a reaction product of three identical molecules. Trimers are typically encountered as cyclic trimers. Chemical compounds that very easily form trimers are aliphatic isocyanates and cyanic acids as an early intermediate in a polymerisation process, see also oligomers. Hydrogen Bonding is occasionally part of this process. For example, water (H2O) can form the trimer (H2O)3.