CAREER: Enabling Sustainable Polymer Synthesis through Design of New Catalysts

在这个由化学系化学催化计划资助的项目中，普林斯顿大学化学系的布拉德利·卡罗教授正在研究如何从乙烯、丙烯酸衍生物、一氧化碳和二氧化碳等丰富的工业化学品中直接合成新型催化剂，以制备功能聚合物。聚合物是长链有机分子，它们的许多性质来自于链之间的纠缠和相互作用。聚合物已经成为我们日常生活中无处不在的材料，影响到大多数行业，包括农业和食品、健康和安全以及交通运输。聚乙烯是所有聚合物中最常见的(2014年生产了1870亿磅)，对其进行修饰以包括碳和氢以外的原子，可以产生独特的新材料性能，例如增强的生物降解性，这可能会将这一基本聚合物类别的应用扩展到新的领域。催化生产方法有望以可持续的方式实现这些目标，因为与仍在商业上实践的标准路线相比，它们具有更低的能源需求和更好的分子结构控制。该项目通过研究和科学交流培训，为研究生和本科生提供综合研究和教育体验。卡罗教授正在开发一项计划，旨在接触到特伦顿和纽瓦克地区高中的教育工作者，其中还包括培训研究生与其他人交流和互动的计划。这些学校有很大比例的学生，其族裔在化学领域的代表性不足，因此，这些计划在扩大STEM领域代表性不足学生的参与方面具有很大的作用。在这个项目中，Carrow教授利用螯合膦-膦二胺(PPDA)配体的灵活结构作为平台，系统地研究了与乙烯与丙烯酸酯、一氧化碳或二氧化碳的催化插入共聚有关的第10族金属络合物的烯烃迁移插入反应。插入聚合催化剂受到极性单体包裹后聚合物配体中官能团的分子内配位的强烈抑制，这通常会将催化剂效率压低到实际阈值以下。这些限制已经持续多年，设计下一代催化剂，特别是贱金属催化剂，具有显著改善的活性、分子量控制和序列分布控制，仍然需要基本的力学见解。卡罗教授正在从钯和镍的络合物的反应中发展结构-活性关系，每个络合物都有一个特有的PPDA配体，以解开配体电荷、原子性和空间阻碍对模型催化剂休眠状态络合物的化学计量反应速率的整体影响。催化歧管中的平行研究正在将这些静电、感应和立体作用力与涉及乙烯和共聚单体的相对繁殖和链转移速率的变化相关联，这些变化最终决定了催化剂对聚合物序列分布、微观结构和分子量的控制。

In this project funded by the Chemical Catalysis Program of the Chemistry Division, Professor Bradley Carrow of the Department of Chemistry at Princeton University is studying the synthesis of new catalysts to prepare functional polymers directly from abundant industrial chemicals, such as ethylene, acrylic acid derivatives, carbon monoxide, and carbon dioxide. Polymers are long chain organic molecules that derive many of their properties from the entanglements and interactions between the chains. Polymers have become ubiquitous materials in our daily lives, impacting most industries, including agriculture and food, health and safety, as well as transportation. The modification of polyethylene, the most common of all polymers (187 billion pounds produced in 2014), to include atoms other than carbon and hydrogen can give rise to distinct new material properties, such as enhanced biodegradability, that could extend the applications of this essential polymer class into new arenas. Catalytic production methods are poised to accomplish these goals in a sustainable fashion because they occur with lower energy demand and better molecular structure control than standard routes that are still practiced commercially. The project is providing an integrated research and educational experience for graduate and undergraduate students through research and science communication training. Professor Carrow is developing a program designed to reach educators from Trenton and Newark area high schools that also includes plans to train graduate students to communicate and interact with people who are not "fellow experts." These schools have a large proportion of students whose ethnicity is underrepresented in the chemistry field, and therefore the plans have a strong component of broadening the participation of underrepresented students in STEM fields. In this project, Professor Carrow is leveraging the flexible structure of chelating phosphine-phosphonic diamide (PPDA) ligands as a platform for systematic studies of alkene migratory insertion reactions involving group 10 metal complexes relevant to catalytic insertion copolymerizations of ethylene with acrylates, carbon monoxide, or carbon dioxide. Insertion polymerization catalysts are strongly inhibited by intramolecular coordination of a functional group within a polymeryl ligand following polar monomer enchainment, which generally depresses catalyst efficiencies below practical thresholds. These limitations have persisted over many years, and fundamental mechanistic insights are still needed for the design of next generation catalysts, particularly those of base metals, with significantly improved activity, molecular weight control, and sequence distribution control. Professor Carrow is developing structure-activity relationships from reactions of palladium and nickel complexes each with a characteristic PPDA ligand to disentangle the ensemble effects of ligand charge, donicity, and steric encumbrance on the rates of stoichiometric reactions involving model catalyst resting state complexes. Parallel studies within a catalytic manifold are correlating these electrostatic, inductive, and steric forces with changes in relative propagation and chain transfer rates involving ethylene and a comonomer, which ultimately dictate the catalyst control over polymer sequence distribution, microstructure, and molecular weight.