A copolymer of ethylene with silane groups containing comonomer that is produced in a high pressure radical polymerization process comprising the steps of: (a) compressing ethylene together with the silane groups containing comonomer under pressure in a compressor, wherein a compressor lubricant is used for lubrication, (b) polymerizing ethylene together with the silane groups containing comonomer in a polymerization zone, (c) separating the obtained ethylene from the unreacted products and recovering the separated ethylene copolymer in a recovery zone, wherein in step a) the compressor lubricant comprises a mineral oil and ethylene copolymer has a silane groups containing comonomer content of 0.5 to 3 wt % and an MFR2 of 0.3 to 10 g/10 min. The co-polymer of ethylene with silane groups containing comonomer can be used.