Abstract: There are disclosed novel homopolymers of 5-aryl-2-norbornene, and novel interpolymers of 5-aryl-2-norbornene with at least one other cyclic or acyclic alkene, and hydrogenated hydrocarbon resins resulting from hydrogenation of the homopolymers and interpolymers. The products are particularly useful as tackifiers. Also disclosed is a novel process for preparing the homopolymers and interpolymers of the 5-aryl-2-norbornene, wherein there is used as the polymerization catalyst, a Friedel-Crafts catalyst, such as aluminum chloride or boron trifluoride.