Bio-based healable thermoset polyurethanes containing dynamic phenol–carbamate bonds derived from quercetin and poly(trimethylene glycol)

Bio-based healable polymer networks have attracted considerable attention because of their carbon neutrality and healability, which lead to long material life. In this study, mixtures of quercetin (QC), a 1/2 adduct (PO2PDI) of poly(trimethylene glycol) (PO3G) and 1,5-pentamethylene diisocyanate (PDI), and PDI trimer (PDIT) [QC (mol-OH):PO2PDI (mol-NCO):PDIT (mol-NCO) = 5(10 + α)/3:10:α] were thermally cured to produce fully bio-based polyurethane networks (BPUN-α, α = 0, 3, and 5), and the influence of the molar ratios of QC:PO2PDI:PDIT on the thermal, mechanical, and healing properties of the BPUNs were investigated. Differential scanning calorimetry revealed that BPUN-0 exhibited only one glass transition temperature (T_g), whereas BPUN-3 and BPUN-5 showed two T_gs ascribed to the glass transition of the PO2PDI/QC and QC/PDIT-rich components in consistent with the result of dynamic mechanical analysis. The tensile strength and modulus of BPUN-α increased with increasing α owing to the increasing crosslinking density. The decomposition test of the cured product of QC and PDI in excess 1-hexanol revealed that the dissociation of phenol-carbamate bonds started at approximately 100–120 ℃. The BPUNs were subjected to healing by pressing at 120 ℃ under 1 MPa for 1 h at least thrice; the healing efficiency in terms of tensile strength for the once-healed BPUNs was higher than 90%.