Molecular knots and entanglements form randomly and spontaneously in both biological and synthetic polymer chains. It is known that macroscopic materials, such as ropes, are substantially weakened by the presence of knots, but until now it has been unclear whether similar behaviour occurs on a molecular level. Here we show that the presence of a well-defined overhand knot in a polymer chain substantially increases the rate of scission of the polymer under tension (≥2.6× faster) in solution, because deformation of the polymer backbone induced by the tightening knot activates otherwise unreactive covalent bonds. The fragments formed upon severing of the knotted chain differ from those that arise from cleavage of a similar, but unknotted, polymer. Our solution studies provide experimental evidence that knotting can contribute to higher mechanical scission rates of polymers. It also demonstrates that entanglement design can be used to generate mechanophores that are among the most reactive described to date, providing opportunities to increase the reactivity of otherwise inert functional groups.

分子结和缠结在生物和合成聚合物链中随机且自发地形成。众所周知，宏观材料（例如绳索）会因结的存在而大大削弱，但到目前为止，尚不清楚在分子水平上是否会发生类似的行为。在这里，我们表明，聚合物链中存在明确的反手结会显着增加溶液中聚合物在张力下的断裂速率（速度≥2.6倍），因为收紧结引起的聚合物主链变形会激活不反应的共价键。打结链断裂时形成的片段与类似但未打结的聚合物裂解时形成的片段不同。我们的解决方案研究提供了实验证据，表明打结有助于提高聚合物的机械断裂率。它还表明，纠缠设计可用于生成迄今为止描述的最具反应性的机械载体，为提高其他惰性官能团的反应性提供了机会。