In 2005 there were "several types of commercial cyclic olefin copolymers based on different types of cyclic monomers and polymerization methods. Cyclic olefin copolymers are produced by chain copolymerization of cyclic monomers such as 8,9,10-trinorborn-2-ene (norbornene) or 1,2,3,4,4a,5,8,8a-octahydro-1,4:5,8-dimethanonaphthalene (tetracyclododecene) with ethene (such as Polyplastics subsidiary TOPAS Advanced Polymers TOPAS, Mitsui Chemicals APEL), or by ring-opening metathesis polymerization of various cyclic monomers followed by hydrogenation (Japan Synthetic Rubbers ARTON, Zeon Chemicals Zeonex and Zeonor)." These later materials using a single type of monomer are more properly named cyclic olefin polymers (COP).