Stimulus-responsive polymers containing dynamic bonds enable fascinating properties of self-healing, recycling and reprocessing due to enhanced relaxation of polymer chain/network with labile linkages. Here, we study the structure and properties of a new type of thermoplastic polyurethanes (TPUs) with trapped dynamic covalent bonds in the hard-phase domain and report the frustrated relaxation of TPUs containing weak dynamic bond and π-π interaction in hard segments. As detected by rheometry, the aromatic TPUs with alkyl disulfide in the hard segments possess the maximum network relaxation time in contrast to those without dynamic bonds and alicyclic TPUs. In situ FTIR and small-angle scattering results reveal that the alkyl disulfide facilitates stronger intermolecular interaction and more stable micro-phase morphology in π-π interaction based aromatic TPUs. Molecular dynamics simulation for pure hard segments of model molecules verify that the presence of disulfide bonds leads to stronger π-π stacking of aromatic rings due to both enhanced assembling thermodynamics and kinetics. The enhanced π-π packing and micro-phase structure in TPUs further kinetically immobilize the dynamic bond. This kinetically interlocking between the weak dynamic bonds and strong molecular interaction in hard segments leads to much slower network relaxation of TPU. This work provides a new insight in tuning the network relaxation and heat resistance as well as molecular self-assembly in stimulus-responsive dynamic polymers by both molecular design and micro-phase control toward the functional applications of advanced materials.

由于具有不稳定键的聚合物链/网络增强了松弛，因此含有动态键的刺激响应聚合物能够实现令人着迷的自我修复，回收和再加工性能。在这里，我们研究了一种新型热塑性聚氨酯（TPU）的结构和性能，该热塑性聚氨酯在硬相域中捕获了动态共价键，并报告了含有弱动态键和π - π相互作用的TPU在硬链段中的受阻弛豫。通过流变仪检测，与不具有动态键和脂环族TPU的芳族TPU相比，在硬链段中具有烷基二硫化物的芳族TPU具有最大的网络弛豫时间。原位FTIR和小角散射结果表明，在基于π-π相互作用的芳香族TPU中，烷基二硫促进了更强的分子间相互作用和更稳定的微相形态。对模型分子的纯硬链段进行的分子动力学模拟证明，由于增强了组装热力学和动力学性能，二硫键的存在会导致芳香环更牢固的π-π堆积。增强的π-πTPU中的堆积和微相结构进一步动力学固定了动态键。硬链段中弱动态键与强分子相互作用之间的动力学连锁导致TPU的网络松弛慢得多。这项工作提供了新的见解，通过分子设计和微相控制，针对先进材料的功能应用，调节了刺激响应型动态聚合物的网络弛豫和耐热性以及分子自组装。