The present invention relates to a process for the preparation of polymer conjugates of indolocarbazole compounds, in particular of polymer conjugates of K-252a and derivatives thereof, by a synthetic route which results in a highly pure product, with a high product yield. In a further aspect the present invention relates to novel polymer conjugates of K-252a and derivatives thereof, wherein the chemical group linking the polymer unity to the K-252a or to the K-252a derivative compound is characterised by a 5- member oxazolidindionic cyclic structure. These novel polymer conjugates are obtained through the novel synthetic route with high purity and high yields.
