Sustainable and malleable polyurethane networks from castor oil and vanillin with tunable mechanical properties

Abstract

Castor oil (CSO)-derived polyurethanes (PUs) are limited by the low mechanical performance and non-reprocessability arisen from their permanently crosslinked structures with high crosslink density and flexible network backbone. In this study, we report malleable polyurethane networks prepared from CSO and hexamethylene diisocyanate with vanillin derived Schiff base (VSB) as a multifunctional monomer. On one hand, VSB with multiple rigid benzene rings and two hydroxyl groups works as a structure modifier to regulate network stiffness and crosslink density of the PUs, which allows us to tailor their mechanical properties over a broad range from soft to tough and hard depending on the content of VSB. On the other hand, VSB with dynamic imine bonds provides the PUs with vitrimeric properties including malleability, thermal processability, and recyclability via network topological rearrangement as a result of imine exchange reaction at elevated temperatures. Consequently, we achieved malleable, processable, and recyclable CSO-derived PU vitrimers with tunable mechanical properties (from elastomer to tough and hard plastics), which would improve the viability and sustainability of CSO-based PUs.