The present invention is directed at a bulkpolymerisation process for the preparation of a polymer (P) comprising the steps of: (i) providing at least one diene monomer (DM) and optionally at least one comonomer (COM); (ii) contacting the at least one diene monomer (DM) and optionally the at least one comonomer (COM) with a catalyst system (CS) forming a reaction mixture (RM); (iii) polymerizing the reaction mixture (RM) comprising the at least one diene monomer (DM) and optionally the at least one comonomer (COM) in at least one reactor vessel (RV); (iv) isolating the polymer (P) obtained from the at least one reactor vessel (RV); wherein the reaction mixture (RM) comprises solvent, diluent and/or dispersant in an amount of ≤10 wt.-%, based on the weight of the reaction mixture (RM); and wherein the conversion rate of the diene monomer (DM) and optionally the comonomer (COM) is ≥80%.