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

This\nwork focuses on designing biobased polyurethane systems possessing\nintrinsic free radical scavenging activity (RSA), exceptional toughness,\nand thermal stability. Initially, divanillyl alcohol (DVO) was synthesized\nthrough oxidative coupling activation of the vanillin precursor, followed\nby reduction of aldehyde groups. Subsequently, polyurethanes denoted\nas RSPU-<i>x</i> (where <i>x</i> is the molar\nratio of DVO) were synthesized, using polycaprolactone diol (OH-PCL–OH)\nas the soft segment and isophorone diisocyanate (IPDI) along with\nDVO as the hard segments. With an increase in the DVO content from\n0 to 0.25, the thermal stability and mechanical properties of RSPU-<i>x</i> were significantly enhanced. Specifically, the maximum\nthermal decomposition temperature rose from 317 to 417 °C, while\nthe toughness shot up from 38.1 MJ/m<sup>3</sup> to 223.9 MJ/m<sup>3</sup>. The improvement of thermal stability is attributed to the\nbiphenyl structure of DVO, which has high bond dissociation energy\nand exceptional free radical scavenging activity, while enhanced toughness\nprimarily results from the introduction of the DVO rigid skeleton,\nwhich disrupts the regularity of PCL chains, thereby inhibiting PCL\ncrystallization behavior. Additionally, RSPU-<i>x</i> also\nexhibited inherent free radical scavenging activity due to the presence\nof Ar–OH groups in the skeletons. The RSA of RSPU-0.25 (DPPH\nand ABTS tests) reached, respectively, 94.21% and 99.24% within 0.5\nh, achieved via the H<sup>+</sup> transfer mechanism. This work presents\na novel strategy for preparing polyurethanes with exceptional thermal\nstability and RSA properties.