Synthesis of Vanillin-Based Polyurethane with Super Thermal Stability and Free-Radical-Scavenging Activity

This work focuses on designing biobased polyurethane systems possessing intrinsic free radical scavenging activity (RSA), exceptional toughness, and thermal stability. Initially, divanillyl alcohol (DVO) was synthesized through oxidative coupling activation of the vanillin precursor, followed by reduction of aldehyde groups. Subsequently, polyurethanes denoted as RSPU-x (where x is the molar ratio of DVO) were synthesized, using polycaprolactone diol (OH-PCL-OH) as the soft segment and isophorone diisocyanate (IPDI) along with DVO as the hard segments. With an increase in the DVO content from 0 to 0.25, the thermal stability and mechanical properties of RSPU-x were significantly enhanced. Specifically, the maximum thermal decomposition temperature rose from 317 to 417 °C, while the toughness shot up from 38.1 MJ/m3 to 223.9 MJ/m3. The improvement of thermal stability is attributed to the biphenyl structure of DVO, which has high bond dissociation energy and exceptional free radical scavenging activity, while enhanced toughness primarily results from the introduction of the DVO rigid skeleton, which disrupts the regularity of PCL chains, thereby inhibiting PCL crystallization behavior. Additionally, RSPU-x also exhibited inherent free radical scavenging activity due to the presence of Ar-OH groups in the skeletons. The RSA of RSPU-0.25 (DPPH and ABTS tests) reached, respectively, 94.21% and 99.24% within 0.5 h, achieved via the H+ transfer mechanism. This work presents a novel strategy for preparing polyurethanes with exceptional thermal stability and RSA properties.