New Strategies for Regulating Non-Living Olefin Polymerization Catalysis

在化学系化学催化项目的支持下，休斯顿大学的Loi Do正在研究如何改进聚烯烃的合成，这种聚合物占全球塑料使用的60%以上。聚烯烃是已知的最具吸引力的合成材料之一，因为它们重量轻，耐水、油和溶剂的破坏，并且能够很容易地塑造成消费品。很大比例的聚烯烃是用一种称为活性聚合的催化过程制造的。然而，这种方法效率低下，因为每个催化剂反应位点只产生一条聚合物链。相反，使用非活性催化剂的聚合反应每个位点产生许多聚合物链。非活性催化剂的主要限制是难以控制其生成的聚合物产物。Do团队的研究将集中在使用地球丰富的金属添加剂来修饰非生物聚合。这项工作旨在开发更可持续的方法来合成聚烯烃，并为以前未知的聚合物结构提供技术上有用的特性。Do团队外展活动的目标是通过创建德克萨斯州化学联盟来提高美国墨西哥湾沿岸地区本科生的研究经验，该联盟专注于共享科学资源和专业知识，交换学生进行培训，主持实地考察，并为学生创造专业网络机会。在这个研究项目中，休斯顿大学的Lo小组致力于提高聚烯烃合成的催化效率和精度。聚烯烃可以用活性或非活性催化剂由烯烃单体合成。活性催化剂对链的生长过程提供了很好的控制，但每个金属只能产生一个聚合物链。相比之下，非活性催化剂缺乏对聚合物链传播的控制，但每个金属提供许多聚合物。由于从活性催化剂中提取的聚烯烃含有很高的金属含量，它们还必须经过进一步的纯化步骤。为了结合生物和非生物反应的好处，Do博士和他的团队正在开发一种基于阳离子的策略，通过配位插入催化来调节聚合。在动态切换条件下，聚合物链生长发生在单一催化剂上，在单金属和双金属形式之间不断相互转化。成功的关键是阳离子交换必须比链生长慢，但比链终止快。Do小组也在设计新的催化剂来实现立体控制聚合功能烯烃。通过将手性金属助剂与共同的催化剂平台配对，将组装手性催化剂库，这将提供使用传统有机支架无法获得的分子结构。由于聚烯烃占全球商业塑料产量的60%以上，因此在工业规模上改进聚烯烃的生产方式可以大大降低成本、能源和环境影响。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

With the support of the Chemical Catalysis program in the Division of Chemistry, Loi Do of the University of Houston is studying how to improve the synthesis of polyolefins, polymers that account for more than 60% of plastics used worldwide. Polyolefins are some of the most attractive synthetic materials known because of their light weight, resistance to damage by water, oil, and solvent, and ability to be easily shaped into consumer items. A large percentage of polyolefins are made using a catalytic process known as living polymerization. However, such processes are inefficient because only one polymer chain is produced for each catalyst reactive site. In contrast, polymerizations using non-living catalysts yield many polymer chains per site. The main limitation with the non-living catalysts is that it is difficult to control the polymer products they generate. The Do team's research will focus on using earth abundant metal additives to modify non-living polymerizations. This work seeks to develop more sustainable ways to synthesize polyolefins and provide access to previously unknown polymer structures with technologically useful properties. The objective of the Do team's outreach activities is to enhance the research experiences of undergraduate students in the Gulf Coast region of the United States by creating a Texas Chemistry Consortium focused on sharing scientific resources and expertise, exchanging students for training, hosting site visits, and creating professional networking opportunities for students.Under this research project, the Lo group at the University of Houston strives to improve catalytic efficiency and precision in polyolefin synthesis. Polyolefins can be synthesized from olefin monomers using either living or non-living catalysts. Living catalysts provide excellent control over the chain growth process but yield only a single polymer chain per metal. In contrast, non-living catalysts lack control over polymer chain propagation but afford many polymers per metal. Because polyolefins derived from living catalysts contain high metal content, they must also be subjected to further purification steps. To combine the benefits of both living and non-living reactions, Dr. Do and his team are developing a cation-based strategy to regulate polymerizations by coordination insertion catalysis. Under dynamic switching conditions, polymer chain growth occurs from a single catalyst that continuously interconverts between the monometallic and bimetallic forms. The key to success is that cation exchange must proceed slower than chain growth but faster than chain termination. The Do group is also designing new catalysts to achieve stereocontrolled polymerization of functional olefins. A library of chiral catalysts will be assembled by pairing chiral metal auxiliaries with a common catalyst platform, which will provide access to molecular structures that are inaccessible using conventional organic scaffolds. Because polyolefins represent greater than 60% of the commercial plastic produced around the world, improvements in the way they are manufactured on an industrial scale could dramatically reduce cost, energy, and environmental impact.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.