Process for the preparation of a polymer comprising monomeric units of ethylene, an α-olefin and a vinyl norbornene whereby the polymer contains 1-5 weight% vinyl nornornene applying as a catalyst system: a. a group 4 metal containing an unbridged catalyst having a single cyclopentadienyl ligand and a mono substituted nitrogen ligand, wherein said catalyst is defined by the formula I: b. an aluminoxane activating compound, c. 0 - 0.20 mol per mol of the catalyst of a further activating compound, wherein Y is ai) a phosphorus substituent defined by the formula: wherein each R 1 is independently selected from the group consisting of a hydrogen atom, a halogen atom, C 1-20 hydrocarbyl radicals which are unsubstituted by or further substituted by a halogen atom, a C 1-8 alkoxy radical, a C 6-10 aryl or aryloxy radical, an amido radical, a silyl radical of the formula: -Si-(R 2) 3 Form. III. wherein each R 2 is independently selected from the group consisting of hydrogen, a C 1-8 alkyl or alkoxy radical, C 6-10 aryl or aryloxy radicals, and a germanyl radical of the formula: -Ge-(R 2') 3 Form. IV. wherein R 2' is independently selected from the group consisting of hydrogen, a C 1-8 alkyl or alkoxy radical, C 6-10 aryl or aryloxy radicals. Cp is a ligand selected from the group consisting of cyclopentadienyl, substituted cyclopentadienyl, indenyl, substituted indenyl, fluorenyl and substituted fluorenyl; X is an activatable ligand and n is 1 or 2, depending upon the valence of M and the valence of X; and M is a group 4 metal selected from the group consisting of titanium, hafnium and zirconium. a. a group 4 metal containing an unbridged catalyst having a single cyclopentadienyl ligand and a mono substituted nitrogen ligand, wherein said catalyst is defined by the formula I: b. an aluminoxane activating compound, c. 0 - 0.20 mol per mol of the catalyst of a further activating compound, wherein Y is ai) a phosphorus substituent defined by the formula: wherein each R 1 is independently selected from the group consisting of a hydrogen atom, a halogen atom, C 1-20 hydrocarbyl radicals which are unsubstituted by or further substituted by a halogen atom, a C 1-8 alkoxy radical, a C 6-10 aryl or aryloxy radical, an amido radical, a silyl radical of the formula: -Si-(R 2) 3 Form. III. wherein each R 2 is independently selected from the group consisting of hydrogen, a C 1-8 alkyl or alkoxy radical, C 6-10 aryl or aryloxy radicals, and a germanyl radical of the formula: -Ge-(R 2') 3 Form. IV. wherein R 2' is independently selected from the group consisting of hydrogen, a C 1-8 alkyl or alkoxy radical, C 6-10 aryl or aryloxy radicals. Cp is a ligand selected from the group consisting of cyclopentadienyl, substituted cyclopentadienyl, indenyl, substituted indenyl, fluorenyl and substituted fluorenyl; X is an activatable ligand and n is 1 or 2, depending upon the valence of M and the valence of X; and M is a group 4 metal selected from the group consisting of titanium, hafnium and zirconium. ai) a phosphorus substituent defined by the formula: wherein each R 1 is independently selected from the group consisting of a hydrogen atom, a halogen atom, C 1-20 hydrocarbyl radicals which are unsubstituted by or further substituted by a halogen atom, a C 1-8 alkoxy radical, a C 6-10 aryl or aryloxy radical, an amido radical, a silyl radical of the formula: -Si-(R 2) 3 Form. III. wherein each R 2 is independently selected from the group consisting of hydrogen, a C 1-8 alkyl or alkoxy radical, C 6-10 aryl or aryloxy radicals, and a germanyl radical of the formula: -Ge-(R 2') 3 Form. IV. wherein R 2' is independently selected from the group consisting of hydrogen, a C 1-8 alkyl or alkoxy radical, C 6-10 aryl or aryloxy radicals. Cp is a ligand selected from the group consisting of cyclopentadienyl, substituted cyclopentadienyl, indenyl, substituted indenyl, fluorenyl and substituted fluorenyl; X is an activatable ligand and n is 1 or 2, depending upon the valence of M and the valence of X; and M is a group 4 metal selected from the group consisting of titanium, hafnium and zirconium.