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Disassociation and Reformation Under Strain in Polymer with Dynamic Metal–Ligand Coordination Cross-Linking

Zhang, Qiuhong, Zhu, Xiangyang, Li, Cheng-Hui, Cai, Yifeng, Jia, Xudong, Bao, Zhenan
Macromolecules 2019 v.52 no.2 pp. 660-668
crosslinking, polymers, rheological properties
Dynamic bonding is a key factor for self-healing and stimuli-response polymeric materials. However, a detailed molecular-level understanding on effects from dynamic bond break and reform from interchain and intrachain cross-linking remains unclear. Here, we apply nonlinear rheological characterization on a polymer cross-linked with dynamic coordination cross-linking. Startup shear measurements and small amplitude oscillatory shear (SAOS) were used to confirm the existence of metal–ligand bond disassociation and reformation; Step extensional measurement was used to further characterize the dynamics of the interchain and intrachain cross-linkings’ disassociation and reformation. We found that dynamic bonds, which are shear rate sensitive, could be disassociated by continuous shear. When the shear or extension rate was much higher than the relaxation rate, both interchain and intrachain coordinated bondings may disassociate, and polymer chains became highly aligned; thus, more interchain reformation took place after extension cessation at higher strain since chain configurations have changed.