Biobased Dynamic Polymer Networks with Rapid Stress Relaxation

Dynamic polymer networks (DPNs) from epoxidized soybean oil (ESO) that incorporate dual dynamic exchange reactions (dual-DERs) and hydroxyl-functionalized silica (HO-SiO2) reinforcement are shown to exhibit rapid stress relaxation and excellent mechanical properties. A disulfide-containing carboxylic acid was used to synthesize the ESO DPNs by simultaneous disulfide metathesis and transesterification reactions that are found to markedly increase the rate of stress relaxation of the networks. HO-SiO2 was used to enhance the mechanical properties while further increasing the rate of stress relaxation. Optimal performance of the ESO/SiO2 DPNs was found at a 3 wt % HO-SiO2 content. In comparison with the neat ESO DPNs, the characteristic stress relaxation time (tau*) of the ESO/SiO2-3 DPNs decreased from 1494 to 898 s at 170 degrees C. The tensile strength and elongation at break, on the other hand, increased by 150 and 113%, respectively. ESO/SiO2-3 DPNs also show excellent self-healing, welding, and recycling properties that are desirable for reuse.