Carbon dioxide and vegetable oil for the synthesis of bio-based polymer precursors, theoretical study of the organocatalyzed synthesis of non-isocyanate polyurethanes

Non-isocyanate polyurethanes (NIPUs) represent a green alternative to the classical synthesis route of polyurethanes involving toxic isocyanates. This “greener” approach based upon renewable feedstocks and carbon dioxide consists in a two-step reaction. In a first step, carbonated vegetable oils are obtained using an appropriate catalyst by the chemical fixation of CO2 onto vegetable oils formerly epoxidized. Finally, the ring-opening polymerization (ROP) of the carbonated vegetable oil by a diamine provides hydroxy urethanes. In this las step, some organocatalysts have been recently proposed that allows achieving good conversion rates in particular in the case of aromatic diamines. However, the activation mechanism of these organocatalysts is not fully elucidated. In this context, the aim of the present project relies on the theoretical study of a model reaction using DFT calculations. Bicyclic guanidine based catalysts, 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) and 7-methyl-TBD (MTBD), were investigated as catalysts for the reaction between propylene carbonate and aliphatic or aromatic amines. The structural ability of TBD to simultaneously give and receive protons was highlighted by the detailed mechanism investigation. The bifunctional activity of TBD significantly reduces the Gibbs energy of the reaction and allows understanding its higher efficiency compared to its methyl counterpart (MTBD).