Novel Biobased Polyurethanes Synthesized from Soybean Phosphate Ester Polyols: Thermomechanical Properties Evaluations

Abstract

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°C in absence of any catalyst show cross-linking densities ranging from 1.8 × 10³ to 3.0 × 10³ M/m³, whereas glass transition temperatures vary from approximately 69 to 82°C. The loss factor (tan δ) curves show single peaks for all these biobased polyurethanes, thus indicating a single-phase system. The storage moduli (G′) at 30°C range from 4 × 10⁸ to 1.3 × 10⁹ Pa. Upon postcure at 150°C, 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 δ intensities decrease as result of restricted chain mobility. Longer exposure time (∼24 h) induces thermal degradation, as evidenced by thermogravimetric analysis (TGA). The dynamic mechanical (DMA) analysis shows that postcure at 100°C for times exceeding 24 h also leads to improved properties. However, cross-linking densities are lower compared to postcure carried out at 150°C.