Recyclable Thermoset-Like Polyurethanes From Renewable Epoxidized Soybean Oil via Dynamic Ester Bond Exchange

A bio-based and recyclable polyurethane (PU) network was developed via dynamic ester bond exchange using triblock polyether diol (EO-PO-EO), pyromellitic dianhydride (PMDA), and epoxidized soybean oil (ESO) as the renewable crosslinker. Varying ESO content (20-100 mol%) enabled control over the crosslinking density and mechanical performance. The 50 mol% ESO formulation exhibited the best overall properties: tensile strength of 202.2 kPa, Young's modulus of 1003.2 kPa, Shore 00 hardness of 90, and crosslinking density of 0.2 mol cm(-3). Thermal degradation began above 300 degrees C for all samples. Excessive ESO (> 50%) led to reduced mechanical strength due to steric hindrance and incomplete crosslinking. Chemical recyclability was demonstrated using ethylene glycol at 180 degrees C. After two recycling cycles, the T-g remained stable around -30.3 degrees C, while the crosslinking density slightly decreased to 0.1684 mol cm(-3). Stress relaxation time was reduced from 1262 to 825 s, confirming efficient dynamic bond reformation. These findings highlight the potential of integrating renewable feedstocks and reversible chemistry to create sustainable, high-performance, and recyclable PU thermoset-like materials.