Thermally Healable Polyurethanes Based on Furfural-Derived Monomers via Baylis-Hillman Reaction

摘要

Two novel acrylate monomers with diol group, 2-hydroxyethyl 2-(furan-2-yl(hydroxy)methyl)acrylate and methyl 2-(hydroxy(5-(hydroxymethyl)furan-2-yl)methyl)acrylate, were synthesized via Baylis-Hillman reaction in moderate yields. The monomer 2-hydroxyethyl 2-(furan-2-yl(hydroxy)methyl)acrylate was obtained from furfural and 2-hydroxyethyl acrylate (HEA); methyl 2-(hydroxy(5-(hydroxymethyl)furan-2-yl)methyl)acrylate was prepared from 5-hydroxymethl furfural (HMF) and methyl acrylate. The monomer 2-hydroxyethyl 2-(furan-2-yl(hydroxy)methyl)acrylate reacted with toluene diisocyanate (TDI)-derived or hexamethylene diisocyanate (HDI)-derived diisocyanate oligomers to obtain the corresponding linear polyurethane oligmers PU-1T and PU-1H. Similarly, the diol methyl 2-(hydroxy(5-(hydroxymethyl)furan-2-yl)methyl)acrylate reacted with TDI- or HDI-derived diisocyanate oligomers to obtain the corresponding linear polyurethane oligmers PU-2T and PU-2H. The number-average molecular weights of the linear polyurethane oligomers are approximately 300-350 Da. There are furan groups in the linear polyurethane oligomers PU-1T, PU-1H, PU-2T and PU-2H, which makes them capable of undergoing reversible Diels-Alder reaction with 4,4'-bismaleimidodiphenylmethane (BMI) to form the corresponding crosslinked polyurethanes CPU-1T, CPU-1H, CPU-2T and CPU-2H. Pencil hardness of CPU-1T, CPU-1H, CPU-2T and CPU-2H are 3H, 2H, 2H and HB, respectively. Glass transition temperatures of CPU-1T, CPU-1H, CPU-2T and CPU-2H are 104.8, 97.6, 5.1 and 1.2 degrees C, respectively. TGA analysis shows that Td(90) values of the CPUs range from 180 to 250 degrees C. Furthermore, the reversible crosslinked polyurethanes CPU-1T and CPU-1H can be completely self-healed at 90 degrees C for 3 h, while CPU-2T and CPU-2H can self-heal at 80 degrees C for 3 h presumably due to their low glass transition temperatures.