10 g of a sustainable TPU was synthesized in a conventional two-step process with MDI as the diisocyanate, PTHF 650 as the polyether polyol and betulin as the chain extender. A prepolymer NCO/OH number (iNCO) of 3 and a final iNCO = 1 were chosen to obtain a specific rigid polymer with high Tg. The synthesis route is shown in Figure . After overnight to finalize the reaction in a vacuum oven at 50 °C, 100 mg of TPU were dissolved into 5 ml THF at 60 °C. Then, an appropriate amount of plasticizer is added, and the resulting solution is stirred for 5 min. The mixture is poured into a glass Petri dish and left overnight in a fume hood to evaporate the solvent. Traces of solvent are then removed in a vacuum oven at 50 °C for 6 h.