Organometallic Reactivity of Metal-Centered Radicals

该项目由无机、生物无机和有机金属化学项目资助，将支持宾夕法尼亚大学的Bradford Wayland教授继续研究金属中心自由基及其与有机自由基的反应，特别是在烯烃聚合的背景下。将探讨在烯烃自由基聚合中建立准活性聚合的新方法的最新发现。这是通过使用以金属为中心的自由基来捕获聚合物的生长端来实现的。这一策略成功的关键特征是形成的金属-碳键的强度，它必须足够弱，反应可以迅速可逆，以允许容易的链生长。活性自由基聚合将为生产只能通过自由基引发聚合的低分散性烯烃均聚物和嵌段共聚物提供新的途径。最初的研究将集中在使用烷基钴四聚乙烯基卟啉配合物来启动和控制丙烯酸酯的活性自由基聚合，并为建立设计促进类似活性聚合过程的金属配合物的指导标准提供原型。实验概述了确定各种潜在有用的烷基衍生物的金属-碳键强度。聚合物的性质不仅取决于它们的化学结构，而且还取决于它们的分子量。直到最近，控制分子量，特别是控制某些类型单体的聚合物的单个分子的分子量的分散是很困难的。本研究探索了一种新发现的方法，该方法涉及生成“活的”聚合物链，以控制分子量包括分散。术语“活的”意味着如果单个聚合物分子被添加到系统中，它们能够添加更多的单体单元。这允许使用嵌段聚合策略，其中将第二种类型的单体添加到活性聚合物中，以便将新类型聚合物的区域添加到原始链上。通过交替添加两种（或更多）类型的单体，可以制备具有新材料性能的聚合物，而这些新材料性能不是任何一种单体所具有的特征。

This project, funded by the Inorganic, Bioinorganic and Organometallic Chemistry program, will support Professor Bradford Wayland of the University of Pennsylvania in his continued studies of metal-centered radicals and their reactions with organic radicals, particularly in the context of olefin polymerization. Recent discoveries of new methods for establishing quasi-living polymerization in free-radical polymerization of olefins will be explored. This is accomplished through the use of metal-centered radicals to trap the growing end of the polymer. The key feature to the success of this strategy is the strength of the metal-carbon bond that is formed, which must be sufficiently weak that the reaction is rapidly reversible to allow for facile chain growth. Living radical polymerization will provide a new approach for producing low polydispersity homopolymers and block copolymers of olefins that can only be polymerized by radical initiation. The initial research will center on the use of alkyl cobalt tetramesitylporphyrin complexes to initiate and control living radical polymerization of acrylates and to provide a prototype for establishing guideline criteria for the design of metal complexes that promote similar living polymerization processes. Experiments are outlined to determine the metal-carbon bond strengths of a variety of potentially useful alkyl derivatives. The properties of polymers not only depend upon their chemical structures but also upon their molecular weight. Until recently it has been difficult to control the molecular weight and especially the dispersion of molecular weights of the individual molecules of polymers of certain types of monomers. This research explores a newly discovered way, which involves the generation of `living` polymer chains, to control the molecular weight including dispersion. The term `living` means that the individual polymer molecules are capable of adding more monomer units if they are added to the system. This allows the use of block polymerization strategies in which a second type of monomer is added to the living polymer so that a region of a new type of polymer is added to the original chain. By alternating additions of two (or more) types of monomers, polymers with new material properties that are not characteristic of those of either monomer can be prepared.