Novel biobased polyurethanes synthesized from soybean phosphate ester polyols: Thermomechanical properties evaluations

Biobased polyurethanes from soybean oil - derived polyols and polymeric diphenylmethane diisocyanate (pMDI) are prepared and their thermomechanical properties are studied and evaluated. The cross-linked biobased polyurethanes being prepared from soy phosphate ester polyols with hydroxyl contents ranging from 122 to 145 mg KOH/g and pMDI within 5 min of reaction time at 150 degreesC in absence of any catalyst show cross-linking densities ranging from 1.8 x 10(3) to 3.0 x 10(3) M/m(3), whereas glass transition temperatures vary from approximately 69 to 82 degreesC. The loss factor (tan delta) curves show single peaks for all these biobased polyurethanes, thus indicating a single-phase system. The storage moduli (G') at 30 degreesC range from 4 x 10(8) to 1.3 x 10(9) Pa. Upon postcure at 150 degreesC, the thermomechanical properties can be optimized. Cross-link densities are improved significantly for hydroxyl content of 139 and 145 mg KOH/g at curing time of 24 h. Similarly, glass transition temperature (T-g) and storage moduli around and after T-g are increased. Meanwhile, tan delta intensities decrease as result of restricted chain mobility. Longer exposure time (similar to24 h) induces thermal degradation, as evidenced by thermogravimetric analysis (TGA). The dynamic mechanical (DMA) analysis shows that postcure at 100 degreesC for times exceeding 24 h also leads to improved properties. However, cross-linking densities are lower compared to postcure carried out at 150 degreesC.