Synthesis of bio-based polyurethanes from epoxidized soybean oil and isopropanolamine

Epoxidized soybean oil (ESO) and isopropanolamine were used to synthesize a new polyol mixture for preparation of bio-based polyurethanes. The chemical synthetic route for reaction of ESO with isopropanolamine was analyzed by ¹H-NMR. The results suggested that both ester groups and epoxy groups in ESO had reacted with amino group of isopropanolamine through simultaneous ring-opening and amidation reactions. Epoxy groups in various situations exhibited different reactivity, and the unreacted epoxy groups were further opened by hydrochloric acid. The synthesized polyol mixture had high hydroxyl number of 317.0 mg KOH/g. A series of polyurethanes were prepared by curing the synthesized polyol mixture with 1,6-diisocyanatohexance along with different amount of 1,3-propanediol (PDO) as chain extender. Tensile tests showed that yield strengths of the polyurethanes ranged from 2.74 to 27.76 MPa depending on the content of PDO. Differential scanning calorimetry analysis displayed one glass transition temperature in the range of 24.4-28.7°C for all of the polyurethane samples, and one melt peak at high content of PDO. Thermogravimetric analysis showed that thermal degradations of the polyurethanes started at 240-255°C. In consideration of simple preparation process and renewable property of ESO, the bio-based polyurethane would have wide range of applications.