Using Dynamic Bonds to Enhance the Mechanical Performance: From Microscopic Molecular Interactions to Macroscopic Properties

Zhang, C (Zhang, Chi)^{[ 1,2 ]} ; Yang, ZJ (Yang, Zhijun)^{[ 1,2 ]} ; Duong, NT (Nghia Tuan Duong)^{[ 3 ]} ; Li, XH (Li, Xiaohui)^{[ 4,5 ]} ; Nishiyama, Y (Nishiyama, Yusuke)^{[ 3,6,7 ]} ; Wu, Q (Wu, Qiang)^{[ 1,2 ]} ; Zhang, RC (Zhang, Rongchun)^{[ 8 ]} ; Sun, PC (Sun, Pingchuan)^{[ 1,2,9 ]}

MACROMOLECULES, 2019, 52(13): 5014-5025

DOI: 10.1021/acs.macromol.9b00503

摘要

Polymeric materials combining good mechanical performances with self-healing ability and malleability have attracted dramatic attention, but it presently remains a challenge for the facile fabrication of such high-performance materials, not to mention the atomic-level characterization for understanding the molecular origin of the macroscopic properties. Herein, we proposed a facile strategy to fabricate a dual-cross-linked poly(n-butyl acrylate) polymer material, in which the self complementary quadruple hydrogen bonding interactions between 2ureido-4[1H]-pyrimidinone (UPy) dimers were utilized as the dynamic sacrificial cross-linkages, and thus to enhance the mechanical strength and toughness. The hydrogen bonding interactions between UPy dimers in such synthetic cross-linked polymer material were revealed in detail by selective saturation double-quantum (DQ) solid-state NMR spectroscopy under ultrafast magic-angle spinning beyond 60 kHz. In the meantime, the self-healing capability and recyclability were achieved by utilizing dynamic fast boronic ester transesterification at an elevated temperature. A novel symmetrical diboronic ester cross-linker was developed and employed to enhance the probability of bornoic ester transesterification at an elevated temperature. The boronic ester transesterification was verified on a small molecular model and polymer materials by solution 1H NMR spectroscopy and swelling experiments, respectively, and the cross-linking structure of polymer materials was addressed by low-field proton multiple-quantum NMR spectroscopy and T2 relaxometry. Overall, it is well demonstrated that a combination of diboronic ester bonds and UPy dimers as the chemical and physical cross-linkage, respectively, can impart the rubbery materials with enhanced mechanical stiffness and toughness, good healing and recycling efficiency, and elucidation of the structure-property relationship here can further provide piercing insights into the development of high-performance polymeric materials.