Sustainable Synthesis of Non-Isocyanate Polyurethanes Based on Renewable 2,3-Butanediol

Abstract

In this work, three different cyclic carbonates are obtained from renewable diols and transformed into carbamates by reacting them with renewable 11-amino undecanoic acid methyl ester to synthesize non-isocyanate poly(ester urethane)s in a sustainable manner. A procedure using 2,3-butanediol (2,3-BDO) as a renewable starting material to synthesize a cyclic carbonate with dimethyl carbonate (DMC) is introduced, catalyzed by 1,5,7-triazabicylco[4.4.0]dec-5-ene (TBD). Three purification strategies, i.e., column chromatography, extraction, and distillation, are compared regarding their E-Factors. Propylene glycol (PG) and ethylene glycol (EG) are used as alternative starting materials to broaden the substrate scope and compare material properties, their cyclic carbonates likewise react to carbamates with 11-amino undecanoic acid methyl ester. All carbamates are then polymerized in a bulk polycondensation reaction, yielding non-isocyanate polyurethanes (NIPUs), specifically poly (ester urethane)s, with molecular weights (Mn) up to 10 kDa. Complete characterization is reported using differential scanning calorimetric (DSC), size exclusion chromatographic measurements (SEC), 1H-NMR as well as IR spectroscopy. The rheological properties of the poly(ester urethane)s are investigated in the framework of small amplitude oscillatory shear (SAOS) and uniaxial elongation.