From a bio-based polyphenol diol intermedia to high-performance polyurethane elastomer: Thermal stability, reprocessability and flame retardancy

In this work, a novel bio-based polyphenol diol intermediate (VDP) was synthesized through a combination of aldimine condensation and addition reactions, utilizing vanillin, 4,4'diamino diphenylmethane (DDM), and 9,10-dihydro-9-oxa-10-phospha-phenanthrene-10-oxide (DOPO) as reactants, then various contents of VDP was introduced covalently into the polyurethane backbone. The integration of VDP has notably improved the flame retardancy of polyurethane elastomer, the limiting oxygen index (LOI) of the elastomer was elevated from 23% to 30%, and reaches V-0 rating in the UL-94 vertical burning test. The enhancement of flame retardancy is attributed to the introduction of VDP units, which not only generate PO· and PO₂∙ that can capture active free radicals during combustion, but also releases non-flammable gases to improve the flame-retardant effect. Moreover, the VDP enhances the decomposition activation energy values (E_α) from 109.3 to 227.6 KJ/mol at mass loss rate (α) = 10%, which is attributed to the rigid benzene ring structure of VDP that significantly enhances the intermolecular interactions within the polyurethane chains. Furthermore, the elastomer shows excellent rebound resilience and reprocessability, retaining 98.6% of its original mechanical properties after multiple cycles of hot-press remolding and solvent casting.