Gu Yuwei, Schauenburg Dominik, Bode Jeffrey W, Johnson Jeremiah A
Department of Chemistry , Massachusetts Institute of Technology , 77 Massachusetts Avenue , Cambridge , Massachusetts 02139 , United States.
Laboratorium für Organische Chemie, Department of Chemistry and Applied Biosciences , ETH Zürich , 8093 Zürich , Switzerland.
J Am Chem Soc. 2018 Oct 31;140(43):14033-14037. doi: 10.1021/jacs.8b07967. Epub 2018 Oct 17.
The chemical and topological structure of polymer networks can seldom be orthogonally controlled. For example, novel network topologies are often accessed via the direct incorporation of supramolecular assemblies into the network structure, introducing potentially undesirable chemical components. Here, we address this deficiency by programming topology into network precursors through the incorporation of self-assembly motifs in leaving groups, which become "traceless topological modifiers." Our method enables us to control polymer network topology using self-assembled structures as templates that are not themselves incorporated into the network. We demonstrate this strategy using a model network formed through potassium acyltrifluoroborate (KAT) ligation. Two four-arm polyethylene glycol (PEG)-based star polymers prepared with either O-ethyl or O-octyl carbamoyl hydroxylamine chain ends serve as network precursors, where differences in chain end hydrophobicity produce different self-assembly states in solution. Addition of a bis-KAT reagent to these star polymers induces amide bond formation and concomitant expulsion of the ethyl or octyl traceless topological modifiers, producing topologically isomeric PEG gels with identical chemical compositions yet vastly different physical properties. This work highlights the impact of topology on polymer network properties and provides a new strategy, traceless topological modification, for polymer network design.
聚合物网络的化学和拓扑结构很少能被正交控制。例如，新型网络拓扑结构通常是通过将超分子组装体直接纳入网络结构来实现的，这会引入潜在的不良化学成分。在这里，我们通过在离去基团中引入自组装基序，将拓扑结构编程到网络前驱体中，从而解决这一缺陷，这些离去基团成为“无痕拓扑修饰剂”。我们的方法使我们能够使用自组装结构作为模板来控制聚合物网络拓扑结构，而这些模板本身并不纳入网络。我们使用通过酰基三氟硼酸钾（KAT）连接形成的模型网络来证明这一策略。两种以O - 乙基或O - 辛基氨基甲酰羟胺链端制备的四臂聚乙二醇（PEG）基星形聚合物用作网络前驱体，链端疏水性的差异在溶液中产生不同的自组装状态。向这些星形聚合物中加入双KAT试剂会诱导酰胺键形成，并伴随乙基或辛基无痕拓扑修饰剂的排出，从而产生具有相同化学组成但物理性质差异极大的拓扑异构PEG凝胶。这项工作突出了拓扑结构对聚合物网络性质的影响，并为聚合物网络设计提供了一种新策略——无痕拓扑修饰。
