Star polymers with reactive isocyanate end groups were prepared via the end capping of hydroxy-terminated star polyether polyols with toluene diisocyanate (TDI; 80% = 2,4 TDI, 20% = 2,6 TDI). The multifunctional polyols and TDI were reacted in bulk without a catalyst. This procedure was optimal in regard to the product yield, minimizing unfavorable coupling side reactions and avoiding crosslinking reactions. The experimental results were based on theoretical studies of the reaction kinetics.