Process for substantially gel-free polymerization of norbornene with dicyclopentadiene

A process comprising polymerization of a norbornene-type monomer with about 0% to about 95% by weight of dicyclopentadiene, based upon total polymer weight, said norbornene-type monomer having the formula ##STR6## where X is hydrogen or an alkyl group containing from 1 to 6 carbon atoms, said polymerization being conducted in the presence of

• 1. catalyst comprising (a) at least one compound selected from the group consisting of dialkylaluminum iodides, alkylaluminum diiodides and mixtures of trialkylaluminum compounds with elemental iodine wherein each alkyl group contains from 2 to 8 carbon atoms, (b) at least one dialkylaluminum chloride or alkylaluminum dichloride wherein each alkyl group contains from 2 to 8 carbon atoms and (c) at least one tungsten compound soluble in the monomer mixture or in a solvent selected from the group consisting of aliphatic and cycloaliphatic hydrocarbon solvents containing 4 to 10 carbon atoms and liquid or easily liquified aromatic hydrocarbon solvents containing 6 to 14 carbon atoms, wherein the molar ratio of said (a) to said (b) is from about 0.1/1 to about 10/1, the catalytically effective amount of the combined total of said (a) and (b) is from about 0.25 to about 10 millimoles per mole of monomer, said (a) and (b) are charged before said (c), the molar ratio of the combined total of (a) and (b) to (c) is from about 1/1 to about 80/1 moles per mole, and the molar ratio of said elemental iodine to said trialkylaluminum compound is from about 0.25/1 to about 6/1 moles per mole, and
• 2. at least one nonconjugated acyclic olefin containing from 2 to 12 carbon atoms and having at least one hydrogen on each double-bonded carbon atoms, said acyclic olefin being used in a molar ratio to monomer from about 0.0001/1 to about 0.3/1 mole per mole.