Basic Study on Novel Molecule-Based Magnetic Polymers and Homogeneous Magnetic Fluids

本课题主要研究具有高居里温度（Tc）的分子基磁性聚合物的设计、合成和表征。将合成一系列具有四羧基单元或稳定自由基（例如，磺酰基自由基或硫胺基自由基）的电子受体单体，每个单体将与具有长柔性侧链的含二茂铁和二茂铁的单体反应，以获得分子基磁性聚合物。这种聚合物通过沿大分子链的二茂铁或双二茂单元的强电子供体与四氰基单元或稳定自由基的强电子受体之间的共价键形成分子内交换相互作用。由于二茂铁（或双二茂铁）单元和四氰基（或稳定自由基）的极化，会发生分子间的超交换偶联，大分子链的纠缠将使一维自旋偶联扩展到三维。合成的聚合物的磁性能将用磁强计来表征。x射线衍射将证实合成的聚合物不含任何杂质，如氧化铁，电子自旋共振光谱将证实合成的聚合物中存在自旋相互作用。由于所使用的含二茂铁或二二茂铁的单体上存在长柔性侧链，这种基于分子的磁性聚合物预计可溶于普通溶剂。这样的前景会怎样？开门？发展新一代均质磁流变（MR）流体，与目前工业使用的传统磁流变流体大不相同，后者是非常重的磁性颗粒（氧化铁或铁氧体）悬浮在轻载体液体中，存在严重的沉淀和聚集问题。PI将研究新一代均相MR流体流变行为的基本原理，该流体将由本研究中合成的聚合物制备。智力优势：虽然小分子有机磁体具有低居里温度（远低于室温）的报道，但在过去的三十年中，许多研究小组试图开发具有高居里温度（远高于室温）的真正基于分子的磁性聚合物。这项研究如果成功，将为聚合物合成、电子结构化学和材料化学开辟新的领域，并刺激理论家发展大分子磁性的新理论，因为目前可用的磁性理论涉及小分子有机磁体。高Tc分子基磁性聚合物可能表现出许多理想的特性，包括溶解度、可加工性和合成可行性，并可能具有实际应用。该项目为如何设计具有高Tc的分子基磁性材料提供了新的见解。它还可以从根本上推进稳定自由基的配位化学。更广泛的影响这项研究可能会对几个科学工程学科产生广泛的影响，包括聚合物化学、有机金属/配位化学、凝聚态物理和流变学，以发展一种均匀磁流变流体的新理论。该研究项目的成功完成可能会导致合成目前尚不存在的具有高Tc的新型分子基磁性聚合物的新方法，并可能对新一代新型磁性聚合物的制造工艺以及广泛使用磁流变液的汽车工业产生影响。这项研究将是高度跨学科的；研究生将接触到在新型聚合物的设计和合成及其表征方面的广泛研究经验，这将为他们未来的职业生涯提供广度和灵活性。

CBET-0755763, HanThis research focuses on the design, synthesis, and characterization of molecule-based magnetic polymers having high Curie temperature (Tc). A series of monomers having tetracyano units or stable radicals (e.g., verdazyl radical or thioaminyl radical) for electron acceptor will be synthesized and each of the monomers will be reacted with a ferrocene- and biferrocene-containing monomer with long flexible side chains to obtain molecule-based magnetic polymers. Such polymers will form intramolecular exchange interactions through covalent bonding between the strong electron donor of ferrocene or biferrocene units along the macromolecular chains with the strong electron acceptor of tetracyano unit or stable radical. The intermolecular super exchange coupling will occur due to the polarization of both ferrocene (or biferrocene) units and tetracyano units (or stable radicals), and the entanglement of macromolecular chains will facilitate the expansion of one-dimensional spin coupling into a three-dimensional one. The magnetic properties of the polymers synthesized will be characterized using a magnetometer. X-ray diffraction will be employed to confirm that the polymers synthesized do not contain any impurities such as iron oxide, and electron spin resonance spectrometry will be employed to confirm the presence of spin interactions in the polymers synthesized. Owing to the presence of long flexible side chains on the ferrocene- or biferrocene-containing monomers used, such molecule-based magnetic polymers are expected to be soluble in common solvents. Such a prospect will ?open the door? to the development of a new generation of homogeneous magnetorheological (MR) fluids, quite different from the conventional MR fluids in current industrial use that are suspensions of very heavy magnetic particles (iron oxide or ferrite) in a light carrier liquid which are subject to serious problems of sedimentation and aggregation. The PI will investigate the fundamentals of the rheological behavior of a new generation of homogeneous MR fluids that will be prepared from the polymers synthesized in this research.INTELLECTUAL MERITAlthough small-molecule organic magnets having low Curie temperature (Tc) (much lower than room temperature) have been reported, during the past three decades many research groups have tried to develop truly molecule-based magnetic polymers having high Tc (much higher than room temperature). This research, if successful, will pave new frontiers in polymer synthesis, electronic structure chemistry, and materials chemistry, as well as stimulate theorists to develop new theory for magnetisms of macromolecules, since the currently available theories of magnetism deal with small-molecule organic magnets. High Tc molecule-based magnetic polymers may exhibit numerous desirable properties, including solubility, processability, and synthetic tenability, and could have practical applications. This project could provide new insights into how to design molecule-based magnetic materials having high Tc. It could also fundamentally advance the coordination chemistry of stable free radicals.BROADER IMPACTSThe research could have a broad impact on several scientific engineering disciplines including polymer chemistry, organometallic/coordination chemistry, condensed matter physics, and rheology for the development of a new theory for homogeneous MR fluids. Successful completion of the research project could lead to new method(s) for the synthesis of novel molecule-based magnetic polymers having high Tc, which do not exist at present, and can have an impact on manufacturing processes for a new generation of novel magnetic polymers and also the automotive industry that makes extensive use of magnetorheological fluids. The research will be highly interdisciplinary; graduate students will be exposed to a wide range of research experiences in the design and synthesis of novel polymers and their characterization, which will provide breadth and flexibility for their future careers.