C 2813 (OTTO) Cyclopentadiene (dimer) 90% Cas 77-73-6 - used in resins, particularly unsaturated polyester resins. It plays a major role in inks, adhesives and paints. C 2813 (OTTO) Cyclopentadiene (dimer) 90% Cas 77-73-6 - used as a monomer in polymerization reactions. It is a precursor for the preparation of endo-tetrahydrodicyclopentadiene, which reacts with aluminum chloride at higher temperature to give adamantine. It undergoes a retro-Diels-Alder reaction to yield cyclopentadiene, which acts as ligand in inorganic chemistry.