The results of GPC analysis are presented in Table and Figure in the SI. For all of the macromonomers obtained with different catalyst concentration, an increase of molecular mass and decrease of dispersion was observed, as compared to the starting polyester diol, Priplast 1838. The results presented in Table clearly show that M ̅ n and M ̅ w values were lower with increasing catalyst concentration. The higher catalyst concentrations shorten the total reaction time substantially, because the reaction proceeds simultaneously at a greater number of active centers of the catalyst. At the same time, this effect favors the formation of shorter macrochains. As expected, the dynamic viscosity of the macromonomers reflects the same trend (Fig. and Table ), with a decrease from 172 Pa•s for the material with the lowest concentration of the catalyst to 119 Pa•s for material synthesized with the highest catalyst concentration.