image: (up) The enhancement mechanisms of (i) thermodynamic stability, (ii) kinetic activity, and (iii) external-field responsiveness. (down) Schematic representation of the formation of PIB5Cu and PIB, and explanation of the mechanism of polarized H-bond.
Credit: ©Science China Press
Recently, a research team led by Professor Zhengwei You from the State Key Laboratory of Advanced Fiber Materials at Donghua University published an innovative research in the online edition of National Science Review. By adopting a molecular design strategy that uses copper ion coordination to simultaneously polarize hydrogen bonds, optimize π-π interactions, and catalyze oxime-carbamate bonds, the team has successfully resolved a long-standing dilemma for polymers: balancing thermodynamic stability and kinetic activity.
Prof. You is a leading scientist in the field of polyurethane and elastomers. In this study, their design that integrating copper(II)-p-benzoquinone dioxime carbamate coordination units (Cu-BQDU) into polyurethane brings three major benefits:
- Cu(II) ions coordinate with carbonyl oxygen and oxime nitrogen atoms, altering the electron density of these atoms and significantly boosting hydrogen bond and π-π interaction strength. This gives the Cu-BQDU units ultra-high bond energy, endowing the elastomers with exceptional toughness and thermodynamic stability.
- The coordination bonds extend the conjugated length of molecules and optimize the geometric matching of π-π interactions, which greatly enhances the materials’ photothermal conversion efficiency.
- Acting as Lewis acids, Cu(II) ions catalyze the dynamic exchange of oxime-carbamate bonds, lowering the kinetic energy barrier of the elastomers and thus improving their healing efficiency.
The resulting elastomer, PIB5Cu, has achieved all-round improvement in performance: it boasts the highest toughness (236.0 MJ/m³) among photothermally healable elastomers and delivers top-tier high-temperature stability for dynamically cross-linked polymers (with a characteristic relaxation time of up to 3,500 seconds at 180 °C). Compared to PIB, the non-coordinated counterpart, PIB5Cu shows a 1.8-fold increase in tensile strength, a 2.6-fold rise in toughness, a 1.4-fold improvement in photothermal conversion efficiency, while a 1.9-fold enhancement in healing efficiency—achieving comprehensive performance upgrades.
This innovative molecular design provides a simple and universal solution to the trade-off between thermodynamic stability and kinetic activity in photothermally healable polymers, marking a significant step forward for advanced polymer materials.