this invention is a process for preparing a polymer which comprises contacting pure dicyclopentadiene with a pure tungsten catalyst complex , such as wcl 3 3 , when tributyl tin hydride or triphenyl tin hydride is used as the activator for the polymerization . this process affords a method of polymerization of dicyclopentadiene in which the mixture gels slowly without the use of a rate moderator at 80 ° c . and furthermore cures quite slowly . this delay makes these compositions particularly applicable to reaction injection molding processes . moreover , both the tungsten complexes and the tin activator compounds employed in this invention are relatively insensitive to oxygen and water .