The present invention relates to a process for the preparation of a block copolymer comprising a first type of polyolefin block and at least one type of second polymer block, the process comprising the steps of: A) polymerizing at least one type of olefin monomer using a catalyst system to obtain a first polyolefin block containing a main group metal on at least one chain end; the catalyst system comprising: i) a metal catalyst or metal catalyst precursor comprising a metal from Group 3-10 of the IUPAC Periodic Table of elements; and ii) at least one type of chain transfer agent; and iii) optionally a co-catalyst; B) reacting the first polyolefin block containing a main group metal on at least one chain end obtained in step A) with at least one type of oxidizing agent and subsequently at least one type of metal substituting agent to obtain a first polyolefin block containing at least one functionalized chain end; C) forming at least one second polymer block on the first polyolefin block, wherein as an initiator the functionalized chain end of the first polyolefin block obtained in step B) is used to obtain the block copolymer.