Polyurethanes based on lignin-derived metabolic intermediate with strong adhesion to metals†
Abstract
Lignin is one of the most abundant natural carbon resources. 2-Pyrone-4,6-dicarboxylic acid (PDC) can be produced on a large scale as one of the bio-metabolic intermediates of lignin by using transformed bacteria. In this study, we designed and synthesized novel PDC-based polyurethanes. Although bis(hydroxyethyl)-PDC (BHPDC) was prepared and directly copolymerized with methylenediphenyl 4,4′-diisocyanate (MDI), the resulting polyurethane was inelastic. To solve this issue, the ring-opening polymerization (ROP) of δ-valerolactone (δ-VL) was adopted. The ROP of δ-VL proceeded in a controlled manner in the presence of diphenyl phosphate (DPP) as the catalyst at the hydroxy groups of BHPDC even under bulk conditions, producing the well-defined polyvalerolactone (PVLm) with narrow polydispersity indices. The resulting PVLm was further reacted with MDI to produce biomass-based polyurethanes, PDCPUm. Considering the dual catalytic abilities of DPP for both the ROP and urethane bond formation, the polyurethane synthesis could be performed in one pot without isolation of the PVLm. PDCPUm were thermally stable up to 286 °C and their melting and crystallization temperatures were tuned by the chain length of the PVLm segment. Self-standing films of PDCPUm were prepared via solvent casting. The incorporation of the PDC unit into the polymer chains lowered the crystallinity but did not have significant negative impacts on the mechanical properties. Furthermore, it was revealed that the PDC-based PU exhibits strong adhesion to some metal plates (Al, Cu and Fe).
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