Tandem Ring-Opening/Ring-Closing Metathesis Polymerization: Relationship between Monomer Structure and Reactivity
Tandem Ring-Opening/Ring-Closing Metathesis Polymerization: Relationship between Monomer Structure and Reactivity
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DOI：
10.1021/ja4039278
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发表时间：
2013-07-24
影响因子：
15
通讯作者：
Choi, Tae-Lim
中科院分区：
文献类型：
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作者：
Park, Hyeon;Lee, Ho-Keun;Choi, Tae-Lim
含有低环张力的环烯烃或1-烯烃的单体是烯烃歧化聚合的劣质单体。具有讽刺意味的是，将两个不活跃的官能团保持在一个分子内可以使其成为歧化聚合的优秀单体。最近，我们证明了含有环己烯和丙叉基的单体1通过接力型机理进行了快速串联开环/闭环歧化(RO/RCM)聚合。此外，当使用第三代格拉布斯催化剂时，可以实现活性聚合。在这里，我们通过研究单体的各种结构改变对串联聚合的反应性的影响，对这种串联聚合进行了全面的描述。我们观察到，改变环烯部分的环大小、炔的长度和连接单元不仅影响聚合速度，而且影响Diels-Alder反应的反应性，这是所得到的聚合物的后改性反应。通过H-1核磁共振末端基团分析，研究了串联聚合的反应机理，认为聚合反应是以炔烃优先途径进行的。根据这一机理结论，提出了影响反应戏剧性结构关系的因素。最后，通过串联RO/RCM聚合反应，成功地合成了具有空间挑战性的三取代环烯类单体，得到了具有四取代环烯类的聚合物重复单元。
Monomers containing either cycloalkenes with low ring strain or 1-alkynes are poor monomers for olefin metathesis polymerization. Ironically, keeping two inactive functional groups in proximity within one molecule can make it an excellent monomer for metathesis polymerization. Recently, we demonstrated that monomer 1 having cyclohexene and propargyl moieties underwent rapid tandem ring-opening/ring-closing metathesis (RO/RCM) polymerization via relay-type mechanism. Furthermore, living polymerization was achieved when a third-generation Grubbs catalyst was used. Here, we present a full account on this tandem polymerization by investigating how various structural modifications of the monomers affected the reactivity of the tandem polymerization. We observed that changing the ring size of the cycloalkene moieties, the length of the alkynes, and linker units influenced not only the polymerization rates but also the reactivities of Diels-Alder reaction, which is a post-modification reaction of the resulting polymers. Also, the mechanism of tandem polymerization was studied by conducting end-group analysis using H-1 NMR analysis, thereby concluding that the polymerization occurred by the alkyne-first pathway. With this mechanistic conclusion, factors responsible for the dramatic structure reactivity relationship were proposed. Lastly, tandem RO/RCM polymerization of monomers containing sterically challenging trisubstituted cycloalkenes was successfully carried out to give polymer repeat units having tetrasubstituted cycloalkenes.