The invention relates to a block copolymer comprising a first block of general structure formula (II) and a second block of general structure formula (III) wherein Rx is an organic group having a chain length of from 1 - 9 atoms; Ry is an organic group having a chain length of from 10 - 38 atoms; n1 is at least 2; n2 is at least 2. The invention further relates to a method for preparing such block copolymer using as a catalyst a phenoxy-imine based catalyst having general structure of formula I.