Ring-Expansion Living Cationic Polymerization of Vinyl Ethers: Optimized Ring Propagation
Ring-Expansion Living Cationic Polymerization of Vinyl Ethers: Optimized Ring Propagation
复制标题
乙烯基醚的扩环活性阳离子聚合：优化环增长
DOI：
10.1002/masy.201400044
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发表时间：
2015
影响因子：
--
通讯作者：
M. Sawamoto
中科院分区：
文献类型：
--
作者：
H. Kammiyada;M. Ouchi;M. Sawamoto
对于最近首次使用半缩醛酯嵌入的环状引发剂（1）实现的乙烯基醚的“扩环”活性阳离子聚合，我们研究了反应条件（刘易斯酸催化剂/活化剂、溶剂、温度和试剂浓度）对环链构建的选择性和可控性的影响。例如，刘易斯酸催化剂的选择变得至关重要。具体而言，四溴化锡（SnBr 4）是合适的，用其进行不受干扰的扩环增长而没有不可逆的副反应，以选择性地构建环拓扑结构，尽管伴随着“环融合”成更高分子量的稠环聚合物。然而，可通过降低引发剂（即由其形成的聚合物）的浓度来抑制融合事件。在这些优化的条件下，增长被控制得足以允许单体的顺序添加，以得到扩链的均聚物或嵌段共聚物。因此，扩环阳离子聚合可能是构建具有类似于线性活性聚合物的精确控制的环状聚合物结构的有力工具。
For the “ring‐expansion” living cationic polymerization of vinyl ethers that has recently been achieved for the first time with a hemiacetal ester‐embedded cyclic initiator (1), we investigated the effects of reaction conditions (Lewis acid catalysts/activators, solvents, temperature, and reagent concentration) on the selectivity and controllability for construction of ring chains. For example, the choice of the Lewis acid catalysts turned out crucial. Specifically, tin tetrabrommide (SnBr4) was suitable, with which an undisturbed ring‐expansion propagation proceeded without irreversible side reactions, to selectively construct the ring topology, though accompanied by “ring fusion” into fused ring polymers of higher molelcular weights. The fusion event, however, could be suppressed by decreasing concentration of the initiator, namely, polymers to be formed therefrom. Under these optimized conditions, the propagation is controlled enough to allow sequential addition of monomers to give either chain‐extended homopolymers or block copolymers. Thus, the ring‐expansion cationic polymerization is potentially a powerful tool to construct ring polymer architectures with precision control similar to that for linear living polymers.