Sequence regulation provides an effective approach to controlling the properties of polymer materials. However, this approach remains an open question in the field of dynamic polymers, which emerge as more and more important new generation materials. Herein, we systematically investigate the effect of sequence control of dynamic covalent units in tuning the properties of materials. Different sequence-controlled poly(oxime-urethanes) are designed. The dynamic oxime-urethane groups are relatively dispersed (SCP-1) or concentrated (SCP-2) distributed in their molecular chains. The sequence control strategy provides an efficient way to decouple the mechanical and self-healing performance of polymers, which is one of the most pressing challenges in the field. The relatively dispersed oxime-urethane groups in SCP-1 not only facilitate the reorganization of the dynamic covalent bonds but also increase the probability of the reformation of hydrogen bonds. The reversible dissociation/reassociation of dynamic bonds is conducive to dissipating energy to enhance mechanical performance and promote self-healing properties. As a result, SCP-1 exhibits much faster self-healing than SCP-2, and its tensile strength is nearly twice that of SCP-2. In addition, energy dissipation capacity and degradation behavior also show significant sequence dependence. Overall, this work reveals a new molecular structure-property relationship and provides a powerful strategy to construct high-performance polymers.
Yang Wang,Qingbao Guan,Yue Guo,Lijie Sun,Rasoul Esmaeely Neisiany,Xuran Guo,Hongfei Huang,Lei Yang,Zhengwei You
The limited capacity of typical materials to resist stress loading, which affects their mechanical performance, is one of the most formidable challenges in materials science. Here, we propose a bone-inspired stress-gaining concept of converting typically destructive stress into a favorable factor to substantially enhance the mechanical properties of elastomers. The concept was realized by a molecular design of dynamic poly(oxime-urethanes) network with mesophase domains. During external loading, the mesophase domains in the condensed state were aligned into more ordered domains, and the dynamic oxime-urethane bonds served as the dynamic molecular locks disassociating and reorganizing to facilitate and fix the mesophase domains. Consequently, the tensile modulus and strength were enhanced by 1744 and 49.3 times after four cycles of mechanical training, respectively. This study creates a molecular concept with stress-gaining properties induced by repeated mechanical stress loading and will inspire a series of innovative materials for diverse applications.
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