Kang Minjung, Lin Po-An, Bunch Jordan A, Lipomi Darren J, Arya Gaurav, Cohen Seth M
Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093, United States.
Department of Mechanical Engineering and Materials Science, Duke University, Durham, North Carolina 27710, United States.
J Am Chem Soc. 2025 Feb 26;147(8):6966-6973. doi: 10.1021/jacs.4c17748. Epub 2025 Feb 12.
Polymer-grafted metal-organic frameworks (MOFs) can be used to form free-standing self-assembled MOF monolayers (SAMMs). Polymer chains can be introduced onto MOF surfaces through either the ligands or metal nodes using both grafting-to and grafting-from approaches. However, controlling the grafting density of polymer-grafted MOFs has not yet been achieved, because a means to control the density of grafting sites on the MOF surface has not been developed. In this study, the grafting density of polymer-grafted UiO-66 (UiO = University of Oslo) was controlled by functionalizing a portion of the Zr(IV) secondary building units (SBUs) on a UiO-66 surface with a so-called blocking agent. The remaining sites on the UiO-66 SBUs were functionalized with polymerization initiation groups, and polymers were grown from these sites to obtain particles with variable grafting densities and chain lengths that form SAMMs at an air-water interface. Even under conditions of low grafting density, these materials retain the ability to form SAMMs and their free-standing ability. Changes in particle arrangement within the monolayers were investigated using SEM imaging, and the toughness of the monolayers was evaluated using a film-on-water (FOW) method. Furthermore, coarse-grained molecular dynamics simulations were carried out to elucidate the morphology and mechanical properties of the monolayers. Findings from both experiments and simulations indicate that the toughness of SAMMs is more heavily influenced by the chain length of the grafted polymers than by the overall polymer content in the composite.
聚合物接枝的金属有机框架（MOF）可用于形成独立的自组装MOF单分子层（SAMM）。使用接枝到和接枝自方法，聚合物链可通过配体或金属节点引入到MOF表面。然而，尚未实现对聚合物接枝MOF的接枝密度的控制，因为尚未开发出控制MOF表面接枝位点密度的方法。在本研究中，通过用所谓的封端剂对UiO-66（UiO = 奥斯陆大学）表面上的一部分Zr(IV)二级构筑单元（SBU）进行功能化，来控制聚合物接枝的UiO-66的接枝密度。UiO-66 SBU上的其余位点用聚合引发基团进行功能化，然后从这些位点生长聚合物，以获得具有可变接枝密度和链长的颗粒，这些颗粒在气-水界面形成SAMM。即使在低接枝密度条件下，这些材料仍保留形成SAMM及其独立能力。使用扫描电子显微镜成像研究了单分子层内颗粒排列的变化，并使用水膜（FOW）方法评估了单分子层 的韧性。此外，进行了粗粒度分子动力学模拟，以阐明单分子层的形态和力学性能。实验和模拟结果均表明，SAMM的韧性受接枝聚合物链长的影响比受复合材料中总聚合物含量的影响更大。
