Abstract Chemically crosslinked recyclable photodeformable azobenzene (azo) polymer actuators with good stability (toward organic solvents and higher temperatures) and high processability and reconstruction ability hold great promise in many applications, but their development remains a challenging task. Herein, we report on for the first time a facile and highly efficient post-crosslinking method for addressing this issue. It involves first the synthesis of side-chain polymers bearing N-hydroxysuccinimide (NHS) carboxylate-substituted azo mesogens, fabrication of uniaxially oriented fibers from these azo polymers by the simple melt spinning method, and their subsequent post-crosslinking with cystamine (a diamine containing a disulfide bond) under mild conditions. The resulting chemically crosslinked fibers not only showed rapid and reversible photoinduced bending and unbending at ambient temperature as well as high mechanical strength and good solvent/heating stability, but also could be easily recycled into processable azo polymers in the presence of a reducing agent that can cleave the disulfide bond into thiol groups (i.e., tributylphosphine). In particular, the occurrence of the post-crosslinking reaction only on the thin surface layers of the azo polymer fibers afforded recycled polymers with large amounts of NHS carboxylate-substituted azo mesogens (together with a small amount of oxygen/heating-sensitive thiol-substituted ones) in the first several (at least 5) recycling processes, thus allowing highly efficient reconstruction of photodeformable fibers with excellent photomobile properties by applying melt spinning and post-crosslinking (by using cystamine) methods. The strategy presented here opens the new possibility to the facile and efficient development of various advanced chemically crosslinked recyclable photodriven actuators.

中文翻译：

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通过简便的后交联方法有效制备具有高加工性和重构能力的化学交联可回收光变形偶氮苯聚合物纤维

摘要 化学交联的可回收光可变形偶氮苯 (azo) 聚合物致动器具有良好的稳定性（对有机溶剂和更高的温度）以及高加工性和重建能力，在许多应用中具有广阔的前景，但它们的开发仍然是一项具有挑战性的任务。在此，我们首次报告了一种用于解决此问题的简便高效的后交联方法。它首先涉及合成带有 N-羟基琥珀酰亚胺 (NHS) 羧酸酯取代的偶氮介晶的侧链聚合物，通过简单的熔体纺丝方法从这些偶氮聚合物制造单轴取向纤维，以及随后用胱胺（一种二胺含有二硫键）在温和条件下。由此产生的化学交联纤维不仅在环境温度下表现出快速和可逆的光致弯曲和不弯曲以及高机械强度和良好的溶剂/热稳定性，而且在还原剂存在下可以很容易地再循环成可加工的偶氮聚合物。将二硫键裂解为硫醇基团（即三丁基膦）。特别是，仅在偶氮聚合物纤维的薄表面层上发生后交联反应，为回收聚合物提供了大量 NHS 羧酸酯取代的偶氮介晶（以及少量的氧/热敏感硫醇取代一个）在前几个（至少 5 个）回收过程中，因此，通过应用熔体纺丝和后交联（通过使用胱胺）方法，可以高效地重建具有优异光移动性能的光可变形纤维。这里提出的策略为各种先进的化学交联可回收光驱动执行器的轻松有效开发开辟了新的可能性。