Grignard reagent as activator for polymerization of dicyclopentadiene

In a process for polymerizing a polycyclic cycloolefin wherein a plurality of liquid streams, at least one of which contains a polycyclic cycloolefin and a metathesis polymerization catalyst and at least one of which contains a metathesis polymerization catalyst activator are brought together and immediately injected into a mold where polymerization and molding take place simultaneously, the improvement comprising using as the activator a Grignard reagent having the formula RMgX where R is a cycloalkyl or cycloalkenyl group and X is Cl, Br or I.