Composition of (a) dicyclopentadiene, by itself or in a mixture with a
strained cycloolefin, and (b) a catalytic amount of at least one
carbene-free, divalent-cationic ruthenium or osmium compound as a
single-component catalyst, which contains at least one phosphine group and
a total of 2 to 5 ligands bonded to the metal atom, and which contains
acid anions for charge balancing. The compositions can be polymerized by
means of heat (metathesis polymerization) and are suitable for the
production of shaped articles and coatings.