The selective synthesis of ultrahigh-molar-mass (UHMM, >2 million Da) cyclic polymers is challenging as an exceptional degree of spatiotemporal control is required to overcome the possible undesired reactions that can compete with the desired intramolecular cyclization. Here we present a counterintuitive synthetic methodology for cyclic polymers, represented here by polythioesters, which proceeds via superbase-mediated ring-opening polymerization of gem-dimethylated thiopropiolactone, followed by macromolecular cyclization triggered by protic quenching. This proton-triggered linear-to-cyclic topological transformation enables selective, linear polymer-like access to desired cyclic polythioesters, including those with UHMM surpassing 2 MDa. In addition, this method eliminates the need for stringent conditions such as high dilution to prevent or suppress linear polymer contaminants and presents the opposite scenario in which protic-free conditions are required to prevent cyclic polymer formation, which is capitalized to produce cyclic polymers on demand. Furthermore, such UHMM cyclic polythioester exhibits not only much enhanced thermostability and mechanical toughness, but it can also be quantitatively recycled back to monomer under mild conditions due to its gem-disubstitution.

超高摩尔质量（UHMM，> 200 万道尔顿）环状聚合物的选择性合成具有挑战性，因为需要特殊程度的时空控制来克服可能与所需分子内环化竞争的不良反应。在这里，我们提出了一种违反直觉的环状聚合物合成方法，以聚硫酯为代表，该方法通过超碱介导的偕二甲基化硫代丙内酯的开环聚合进行，然后通过质子猝灭引发大分子环化。这种质子触发的线性到环状的拓扑转变能够选择性地、类似线性聚合物地获得所需的环状聚硫酯，包括 UHMM 超过 2 MDa 的那些。此外，该方法不需要严格的条件，例如高度稀释来防止或抑制线性聚合物污染物，并且提出了相反的方案，其中需要无质子条件来防止环状聚合物的形成，这可以根据需要生产环状聚合物。此外，这种UHMM环状多硫酯不仅表现出大大增强的热稳定性和机械韧性，而且由于其宝石二取代性，它还可以在温和的条件下定量回收回单体。