Catalyst system for producing polyethylene copolymers in a high temperature solution polymerization process

A process for the preparation of an ethylene copolymer, the process comprising polymerizing ethylene and a C4-C10 olefin in a high temperature solution process at a temperature greater than 100° C., in the presence of a catalyst system comprising:

• (i) a metallocene complex of formula (I)
• wherein
• M is Hf or a mixture of Hf with Zr, provided that more than 50% by moles of the complex of Formula I has M=Hf;
• each X is independently a sigma ligand;
• R's are the same or different and are independently selected from the group consisting of linear or branched C1-C10 alkyl, C5-C10 aryl, C6-C20 alkylaryl, and C6-C20 arylalkyl groups, optionally containing up to 2 heteroatoms or silicon atoms;
• R1 is phenyl, which is unsubstituted or substituted by one or up to 5 linear or branched C1-C10 alkyl group(s);
• and
• R2 is a linear or cyclic C3-C20 alkyl group or a branched CR3R4R5 group, wherein R3 is hydrogen or a C1-C20 alkyl group and R4 and R5 are the same or are different and are independently a C1-C20 alkyl group;
• and
• (ii) a boron containing cocatalyst;
• wherein the catalyst system is a homogeneous or non-supported catalyst system, and
• wherein the ethylene copolymer is a copolymer of ethylene and a C4-10 alpha-olefin comonomer with a comonomer content of up to 45 mol %.