Experimental and theoretical assessment of the aminolysis of cyclo carbonate to form polyhydroxyurethanes

Abstract

Polyurethanes (PU) is one of the most used polymers and finds its applications in many modern technologies. The use of not-environmental-friendly chemicals in the actual manufacturing process claims for new more sustainable synthetic strategies. One of these novel routes is the aminolysis of cyclic carbonates resulting in so-called polyhydroxyurethanes (PHU). So far, this ring opening polymerisation (ROP) was mainly investigated considering aliphatic amines. In this study, both aromatic and aliphatic amines without additional catalysts are studied and their reaction behaviours are compared. For this aim, the ROP reactions were monitored by FTIR and NMR spectroscopies. It turned out that aromatic amines do not react in opposition to aliphatic ones. To gain a deeper insight on the reactivity parameters related to this different reaction behavior, simple molecular models were studied by density functional theory methods. Aiming to assess the impact of different conformations and to determine a statistical mean value of the reaction energy molecular dynamic (MD) simulations of a large set of different conformations was sampled. Moreover, the detailed consideration of the electronic density, revealed that the lone pair of the amine nitrogen is delocalised along the π-system of the aromatic compounds. This positive mesomerie effect results in a planarisation of the amine group, in higher reaction barriers and, smaller reaction energies.