A composition comprising: i) a plurality of zinc alkyl compounds and ii) one or more chain growth catalysts at least one of the chain growth catalysts being selected from the group consisting of: a) a complex of Formula wherein M is Ti, Ti, Ti, Zr, Zr, Zr, Hf, Hf, Hf, V, V, V, Nb, Nb, Nb, Nb, Ta, Ta, Ta, Cr, Cr, Mn, Mn, Mn, Fe, Fe, Ru, Ru, Ru, Co, Co, Rh, Rh, Ni, Pd; X represents an atom or group covalently or ionically bonded to the transition metal M; T is the oxidation state of the transition metal M and b is the valency of the atom or group X; Y 1 is C, A 1 to A 3 are each independently CR; and R, R c, R 4, R 5, R 6 and R 7 are each independently selected from hydrogen, halogen, hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl, substituted heterohydrocarbyl or SiR' 3 where each R' is independently selected from hydrogen, halogen, hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl and substituted heterohydrocarbyl; b) a complex of Formula wherein M is Fe, Fe, Ni or Pd, X represents an atom or group covalently or ionically bonded to the transition metal M; R a and R b are each independently selected from hydrogen, halogen, hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl, substituted heterohydrocarbyl or SiR' 3 where each R' is independently selected from hydrogen, halogen, hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl and substituted heterohydrocarbyl, and R a and R b may be joined together to form a ring; R 5 and R 7 are each as defined above; and L is a group datively bound to M; n is from 0 to 5; m is 1 to 3 and q is 1 or 2; c) a complex of Formula wherein M is Ti, Ti, Ti, Zr, Zr, Zr, Hf, Hf, Hf, Cr, Cr, Fe, Fe, Ru, Ru, Ru, Co, Co, Rh, Rh, Ni, Pd, X represents an atom or group covalently or ionically bonded to the transition metal M; R a and R b are joined together to form a phenyl, which is optionally substituted, R x, and R 5 are each independently selected from hydrogen, halogen, hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl, substituted heterohydrocarbyl or SiR' 3 where each R' is independently selected from hydrogen, halogen, hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl and substituted heterohydrocarbyl, and any adjacent ones may be joined together to form a ring; L is a group datively bound to M; n is from 0 to 5; m is 1 to 3 and q is 1 or 2. i) a plurality of zinc alkyl compounds and ii) one or more chain growth catalysts a) a complex of Formula wherein M is Ti, Ti, Ti, Zr, Zr, Zr, Hf, Hf, Hf, V, V, V, Nb, Nb, Nb, Nb, Ta, Ta, Ta, Cr, Cr, Mn, Mn, Mn, Fe, Fe, Ru, Ru, Ru, Co, Co, Rh, Rh, Ni, Pd; X represents an atom or group covalently or ionically bonded to the transition metal M; T is the oxidation state of the transition metal M and b is the valency of the atom or group X; Y 1 is C, A 1 to A 3 are each independently CR; and R, R c, R 4, R 5, R 6 and R 7 are each independently selected from hydrogen, halogen, hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl, substituted heterohydrocarbyl or SiR' 3 where each R' is independently selected from hydrogen, halogen, hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl and substituted heterohydrocarbyl; b) a complex of Formula wherein M is Fe, Fe, Ni or Pd, X represents an atom or group covalently or ionically bonded to the transition metal M; R a and R b are each independently selected from hydrogen, halogen, hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl, substituted heterohydrocarbyl or SiR' 3 where each R' is independently selected from hydrogen, halogen, hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl and substituted heterohydrocarbyl, and R a and R b may be joined together to form a ring; R 5 and R 7 are each as defined above; and L is a group datively bound to M; n is from 0 to 5; m is 1 to 3 and q is 1 or 2; c) a complex of Formula wherein M is Ti, Ti, Ti, Zr, Zr, Zr, Hf, Hf, Hf, Cr, Cr, Fe, Fe, Ru, Ru, Ru, Co, Co, Rh, Rh, Ni, Pd, X represents an atom or group covalently or ionically bonded to the transition metal M; R a and R b are joined together to form a phenyl, which is optionally substituted, R x, and R 5 are each independently selected from hydrogen, halogen, hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl, substituted heterohydrocarbyl or SiR' 3 where each R' is independently selected from hydrogen, halogen, hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl and substituted heterohydrocarbyl, and any adjacent ones may be joined together to form a ring; L is a group datively bound to M; n is from 0 to 5; m is 1 to 3 and q is 1 or 2.