Process for the preparation of an ethylene copolymer comprising polymerizing ethylene and a C 4-10 -alpha-olefin comonomer in a high temperature solution process at a temperature greater than 100°C in the presence of a homogeneous catalyst system comprising: (i) a metallocene complex of formula wherein X M is Hf is a sigma ligand, L is a bridge of the formula -SiR 8 2 -, wherein each R 8 is independently a C 1 -C 20 -hydrocarbyl, tri(C 1 -C 20 -alkyl)silyl, C 6 -C 20 -aryl, C 7 -C 20 -arylalkyl or C 7 -C 20 -alkylaryl n is 0, 1 or 2 R 1 and R 1' are the same or can be different and can be a linear or branched C 1 -C 6 -alkyl group, R 2 and R 2' are the same or are different and are a CH 2 -R 9 group, with R 9 being H or linear or branched C 1 -C 6 -alkyl group R 5 and R 5 ' are the same and are H, or R 5 and R 5 ' are different and can be H or a OR group, wherein R is a C 1 -C 6 -alkyl group R 6 and R 6 are the same or are different and can be H or a C(R 10) 3 group, with R 10 being the same or different and R 10 can be H or a linear or branched C 1 -C 6 -alkyl group, and R 7 and R 7' can be the same or are different and can be H or a linear or branched C 1 -C 6 -alkyl group (ii) an aluminoxane cocatalyst (iii) a boron containing cocatalyst and (iv) optionally an aluminium alkyl compound. (i) a metallocene complex of formula wherein X M is Hf is a sigma ligand, L is a bridge of the formula -SiR 8 2 -, wherein each R 8 is independently a C 1 -C 20 -hydrocarbyl, tri(C 1 -C 20 -alkyl)silyl, C 6 -C 20 -aryl, C 7 -C 20 -arylalkyl or C 7 -C 20 -alkylaryl n is 0, 1 or 2 R 1 and R 1' are the same or can be different and can be a linear or branched C 1 -C 6 -alkyl group, R 2 and R 2' are the same or are different and are a CH 2 -R 9 group, with R 9 being H or linear or branched C 1 -C 6 -alkyl group R 5 and R 5 ' are the same and are H, or R 5 and R 5 ' are different and can be H or a OR group, wherein R is a C 1 -C 6 -alkyl group R 6 and R 6 are the same or are different and can be H or a C(R 10) 3 group, with R 10 being the same or different and R 10 can be H or a linear or branched C 1 -C 6 -alkyl group, and R 7 and R 7' can be the same or are different and can be H or a linear or branched C 1 -C 6 -alkyl group X M is Hf is a sigma ligand, L is a bridge of the formula -SiR 8 2 -, wherein each R 8 is independently a C 1 -C 20 -hydrocarbyl, tri(C 1 -C 20 -alkyl)silyl, C 6 -C 20 -aryl, C 7 -C 20 -arylalkyl or C 7 -C 20 -alkylaryl n is 0, 1 or 2 R 1 and R 1' are the same or can be different and can be a linear or branched C 1 -C 6 -alkyl group, R 2 and R 2' are the same or are different and are a CH 2 -R 9 group, with R 9 being H or linear or branched C 1 -C 6 -alkyl group R 5 and R 5 ' are the same and are H, or R 5 and R 5 ' are different and can be H or a OR group, wherein R is a C 1 -C 6 -alkyl group R 6 and R 6 are the same or are different and can be H or a C(R 10) 3 group, with R 10 being the same or different and R 10 can be H or a linear or branched C 1 -C 6 -alkyl group, and R 7 and R 7' can be the same or are different and can be H or a linear or branched C 1 -C 6 -alkyl group (ii) an aluminoxane cocatalyst (iii) a boron containing cocatalyst and (iv) optionally an aluminium alkyl compound.