Squeezing new life out of polymers.
Squeezing new life out of polymers.
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DOI：
10.1002/anie.201210025
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发表时间：
2013-04
影响因子：
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通讯作者：
Johnathan N. Brantley;K. M. Wiggins;C. Bielawski
中科院分区：
文献类型：
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作者：
Johnathan N. Brantley;K. M. Wiggins;C. Bielawski
聚合物机械化学领域正在经历一场重生，其中宏观力被转化为聚合物基质内的化学转化。独特的或以其他方式动力学上不可接近的化学反应，现在可能的机械不稳定的功能，称为mechanophores，嵌入聚合物，然后受到外源性的机械力。然而，该领域的范式正在发生变化，现在的努力集中在使用武力作为驱动反应性化学物质生产的方法上。特别地，在机械力的作用下产生酸或氧化还原试剂的聚合物是令人感兴趣的，因为这样的材料可以在从通过酸催化的交联反应进行自发修复的自修复系统到机械驱动的合成的范围内的应用中找到实用性。从机械活化的聚合物中生产有价值的小分子仍处于起步阶段，并且用于实现该目标的报告方法通常需要热或化学处理步骤。7]设计仅在机械力下挤出明确定义的化学实体的材料已被证明更具挑战性。在一项开创性的贡献中，摩尔及其同事表明，在超声处理下，二氮可以从聚乙二醇链中位于中心的重氮单元中排出。尽管二氮的化学惰性使其无法用于进一步的反应，但这个例子为摩尔和格里博夫斯基实验室最近的两份报告奠定了基础，这两份报告完美地展示了如何从机械响应材料中产生反应性化学试剂。摩尔小组专注于通过压缩适当官能化的聚合物来产生布朗斯特酸。机械响应材料的设计基于克雷格等人的先前研究，他证明了含有多个偕-二卤代环丙烷（gDHC）部分的聚合物可以进行机械促进的电环重排以提供二卤代烯烃。烯烃产物的随后热处理（165 ℃）导致无机酸（例如，HCl）。为了降低消除反应所需的温度，摩尔等人设想了一种基于茚的类似物，其可以驱动gDHC部分的重排和通过芳构化消除HCl（方案1）。
The field of polymer mechanochemistry, 2] wherein macroscopic forces are translated into chemical transformations within polymeric matrices, is witnessing a rebirth. Unique or otherwise kinetically inaccessible chemical reactions are now possible when mechanically labile functionalities, termed mechanophores, are embedded within polymers and then subjected to exogenous mechanical forces. Paradigms in the field are shifting, however, and efforts are now focusing on using force as a method for driving the production of reactive chemical species. In particular, polymers that generate acids or redox reagents under the action of mechanical force are of interest, as such materials could find utility in applications that range from self-healing systems that undergo spontaneous repair through acid-catalyzed cross-linking reactions to mechanically driven syntheses. The production of valuable small molecules from mechanically activated polymers is still in its infancy, and reported methods for achieving this goal often require a thermal or chemical treatment step. 7] Designing materials that extrude well-defined chemical entities solely under mechanical force has proven considerably more challenging. In a seminal contribution, Moore and co-workers showed that dinitrogen could be expelled from a centrally positioned diazo unit in a poly(ethylene glycol) chain under ultrasonication. Although the chemical inertness of dinitrogen precluded its use in further reactions, this example laid the groundwork for two recent reports from the Moore and Grzybowski laboratories that beautifully demonstrated how reactive chemical reagents can be generated from mechanically responsive materials. The Moore group focused on generating Brønsted acids by compressing appropriately functionalized polymers. The design of the mechanically responsive materials was based on previous studies from Craig et al., who demonstrated that polymers containing multiple gem-dihalocyclopropane (gDHC) moieties could undergo mechanically facilitated electrocyclic rearrangements to afford dihaloalkenes. Subsequent thermal treatment (165 8C) of the olefinic products resulted in the extrusion of mineral acids (e.g., HCl). To reduce the temperature required for the elimination reaction, Moore et al. envisaged an indene-based analogue that could drive the rearrangement of the gDHC moieties and the elimination of HCl through aromatization (Scheme 1).