Cyclopropenes (CPEs) are highly strained cyclic olefins, yet there are surprisingly limited examples leveraging their high strain energy for polymerization. In the past, attempts had been made to polymerize CPEs via cationic and insertion polymerization, but side reactions often gave uncontrolled polymers with mixed backbone structures. Ring-opening metathesis polymerization (ROMP) represents an ideal strategy for polymerizing CPEs to access new types of polymers. The proximity of substituents to the olefin in the small framework of CPEs offers a modular handle to tune the kinetic barrier to propagation by the modulation of the substituents. While the first few studies focused on the homopolymerization of simple alkyl or phenyl disubstituted CPEs, we recently explored the metathesis of a wide range of CPEs with different substituents using Grubbs catalysts and discovered surprising and diverse reactivities that are contingent on the positions, sterics, and electronics of substituents. The observed reactivities ranged from living homopolymerization to catalyst deactivation to single addition to the catalyst without homopropagation. In particular, the exclusively single addition reactivity found in two families of CPEs, with either bis(methanol ester) or phenyl and methanol ester substituents at the allylic position, is unusual for any monomer and perhaps counterintuitive for highly strained cycles. These single-addition CPEs could, however, be copolymerized with low-strain cyclic olefins to generate perfectly alternating copolymers with controlled molecular weights and low dispersity and to introduce degradable backbone linkages. A single equivalent (relative to the active chain end) of such CPEs could also be added to the active chain end of living ROMP polymers to install functional terminal groups or during living ROMP to place single units of functional moieties or side chains at any desired chain locations in narrow-disperse homopolymers and block copolymers. This account summarizes the polymerization of CPEs with a focus on our journey to uncover the rich and unique metathesis reactivities of CPEs and their utility in synthesizing well-controlled and sequence-regulated polymers. It provides the first collective structure–metathesis reactivity relationships for CPEs in the context of polymer chemistry and an understanding of the interactions between the catalyst and the substituents of appended ring-opened CPEs. It may become clear from this Account that the exploration of strained cycles in polymer chemistry can be quite fruitful in discovering new chemistry and accessing new types of polymer materials.

中文翻译：

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环丙烯的聚合：驯服可控和序列调控的聚合物合成的菌株

环丙烯（CPE）是高应变环烯烃，但出乎意料的例子是利用其高应变能进行聚合。过去，曾尝试通过阳离子聚合和插入聚合来聚合CPE，但是副反应通常会产生不受控制的具有混合主链结构的聚合物。开环复分解聚合（ROMP）是使CPE聚合以获取新型聚合物的理想策略。在CPE的小骨架中，取代基与烯烃的接近度提供了模块化的处理方式，可通过调节取代基来调节动力学屏障，以阻止扩散。虽然前几项研究集中在简单的烷基或苯基双取代CPE的均聚上，我们最近使用Grubbs催化剂探索了具有不同取代基的各种CPE的复分解反应，并发现了令人惊奇且多样的反应性，这些反应性取决于取代基的位置，空间和电子性质。观察到的反应性从活性均聚反应到催化剂失活，再到没有均相传播的催化剂一次添加。特别是，在两个CPE家族中，在烯丙基位置带有双（甲醇酯）或苯基和甲醇酯取代基的唯一单一加成反应性，对于任何单体而言都是不寻常的，在高应变循环中可能违反直觉。但是，这些一次添加的CPE可以 将其与低应变环烯烃共聚，以生成分子量可控且分散度低的完美交替共聚物，并引入可降解的骨架键。也可以将此类CPE的单个等价物（相对于活性链末端）添加到活性ROMP聚合物的活性链末端，以安装功能性端基，或在活性ROMP期间将功能性部分或侧链的单个单元放置在任何所需链上在窄分散均聚物和嵌段共聚物中的位置。该报告总结了CPE的聚合反应，重点是我们探索CPE丰富而独特的复分解反应性及其在合成控制良好且受序列调节的聚合物中的用途的过程。它提供了聚合物化学背景下CPE的第一个集体结构-复分解反应性关系，并了解了催化剂与附加的开环CPE的取代基之间的相互作用。从该帐户可能会很清楚地发现，探索聚合物化学中的应变循环在发现新化学方法和使用新型聚合物材料方面可以非常有成果。