Particularly useful polymers are olefin polymers, including homopolymers, particularly polyethylene and the polyalkenamers obtained by polymerizing cycloolefins; copolymers of two or more olefins; and copolymers of one or more olefins, e.g. ethylene or propylene, with one or more olefinically unsaturated comonomers, preferably polar comonomers, e.g. vinyl acetate, acrylic acid methyl acrylate and