Sequence-Regulated Copolymers via Tandem Catalysis of Living Radical Polymerization and In Situ Transesterification
Sequence-Regulated Copolymers via Tandem Catalysis of Living Radical Polymerization and In Situ Transesterification
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DOI：
10.1021/ja211436n
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发表时间：
2012-03-07
影响因子：
15
通讯作者：
Sawamoto, Mitsuo
中科院分区：
文献类型：
--
作者：
Nakatani, Kazuhiro;Ogura, Yusuke;Sawamoto, Mitsuo
作为高分子科学的终极目标，单体的序列调控无疑是一个具有挑战性的问题。为了有效地生产序列控制的共聚物，我们在此开发了通用的串联催化，其同时和/或顺序地涉及甲基丙烯酸酯（单体：RMA）与金属醇盐（催化剂）和醇（ROH）的季铵盐催化的活性自由基聚合和原位酯交换。在活性聚合过程中，R（1）MA与R（2）MA在R2 OH存在下发生酯交换反应，使原料中的瞬时单体组成逐渐变化，得到R（1）MA/R（2）MA梯度共聚物。单体沿着链的梯度顺序由反应条件如温度、催化剂、醇和单体的浓度和/或种类催化控制。多单体单元的序列调节也成功地实现了在一锅通过单体选择性酯交换在并行串联催化和迭代串联催化，分别提供无规梯度共聚物和梯度嵌段对应物。相比之下，通过可变引发聚合或原位酯交换的顺序串联催化导致无规或嵌段共聚物。由于常见和市售试剂（单体、醇、催化剂）的多功能适应性，这种串联催化是设计定制序列调控共聚物的最有效、方便和强大的工具之一。
Sequence regulation of monomers is undoubtedly a challenging issue as an ultimate goal in polymer science. To efficiently produce sequence-controlled copolymers, we herein developed the versatile tandem catalysis, which concurrently and/or sequentially involved ruthenium-catalyzed living radical polymerization and in situ transesterification of methacrylates (monomers: RMA) with metal alkoxides (catalysts) and alcohols (ROH). Typically, gradient copolymers were directly obtained from the synchronization of the two reactions: the instantaneous monomer composition in feed gradually changed via the transesterification of R(1)MA into R(2)MA in the presence of R2OH during living polymerization to give R(1)MA/R(2)MA gradient copolymers. The gradient sequence of monomers along a chain was catalytically controlled by the reaction conditions such as temperature, concentration and/or species of catalysts, alcohols, and monomers. The sequence regulation of multimonomer units was also successfully achieved in one-pot by monomer-selective transesterification in concurrent tandem catalysis and iterative tandem catalysis, providing random-gradient copolymers and gradient-block counterparts, respectively. In contrast, sequential tandem catalysis via the variable initiation of either polymerization or in situ transesterification led to random or block copolymers. Due to the versatile adaptability of common and commercially available reagents (monomers, alcohols, catalysts), this tandem catalysis is one of the most efficient, convenient, and powerful tools to design tailor-made sequence-regulated copolymers.