Magnesium bromide (MgBr₂) was found to be an effective catalyst for the ring-expansion cationic polymerizations of isobutyl vinyl ether (IBVE) initiated by a “cyclic” hemiacetal ester (HAE) bond-based initiator leading to the syntheses of cyclic poly(IBVE)s. Crucial to the achievement is the choice of the quencher (e.g., DMF or DMSO) instead of methanol as well as the realization of living cationic polymerization with an “acyclic” HAE-based initiator under magnesium catalysis. The advantage of MgBr₂ over a conventional catalyst (i.e., SnBr₄) is that several types of cyclic molecules are available as initiators, including a methacrylate type vinylidene group-embedded cyclic compound. The reactive group-carrying initiator allowed the pin-point incorporation of a polar group (e.g., glycerol) into the resultant cyclic polymer via a thiol-Michael addition reaction while retaining the cyclic topology.

中文翻译：

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溴化镁（MgBr2）作为活性阳离子聚合和扩环阳离子聚合的催化剂

溴化镁（MgBr ₂）被发现是异丁基乙烯基醚（IBVE）扩环阳离子聚合反应的有效催化剂，该反应是由基于“环状”半缩醛酯（HAE）键的引发剂引发的，从而合成了环状聚（ IBVE）。实现这一目标的关键是选择淬灭剂（例如DMF或DMSO）代替甲醇，以及在镁催化下使用“非环状”基于HAE的引发剂实现活性阳离子聚合。MgBr ₂优于常规催化剂（即SnBr ₄）是几种类型的环状分子可用作引发剂，包括甲基丙烯酸酯型亚乙烯基基团嵌入的环状化合物。带有反应性基团的引发剂允许在保持环状拓扑结构的同时，通过硫醇-迈克尔加成反应将极性基团（例如甘油）精确地掺入所得的环状聚合物中。