a masterbatch including an ethylene copolymer and at least one ethylene comonomer having at least one polar group , an organic peroxide , and an anti - oxidant , the organic peroxide accounting for 0 . 2 to 100 parts by weight , for 100 parts by weight of the copolymer , and the anti - oxidant accounting for 0 . 02 to 50 parts by weight , for 100 parts by weight of the copolymer . also , methods for preparing the masterbatch and to the uses of said masterbatch for manufacturing insulating layers for electric cables and for limiting or preventing the water tree phenomenon for electric cables .