CAS: Collaborative Research: Processive Ring-Opening Metathesis Polymerization Through Molecularly Confined Catalysts

在化学系大分子、超分子和纳米化学(MSN)计划和化学催化(CAT)计划的支持下，波士顿学院的贾牛和爱荷华州立大学的黄文宇正在开发分子定义笼子中的有机金属Ru配合物催化的开环歧化聚合(ROMP)。尽管ROMP在生产大量功能聚合物方面具有重要意义，但现有技术仍然不能完全防止链转移和终止，特别是当涉及低应变单体时。结果，形成了难以分离的不同大小的线性和环状大分子的混合物。本研究致力于直接解决这一未被满足的挑战，并为进行式嬉戏引入一种独特的策略。在这一策略中，聚合催化剂将被封装在分子定义的笼形结构中，这样，理想情况下，只有单体，而不是新生的聚合物可以访问催化剂。这将抑制由催化剂和新生聚合物之间的相互作用引起的链转移和终止，从而产生具有可控分子量的线形大分子。开发的方法也将应用于以可持续发展为导向的单体的ROMP，这些单体因其低应变而被认为对ROMP具有挑战性。这些单体包括具有低天花板温度的环烯烃和那些由可降解官能团组成的单体。这项研究将为学生提供聚合物合成和可持续性方面的跨学科培训。合作团队还将开发一个为期三周的混合夏季研讨会，旨在将聚合物化学原理和实践引入3D打印。研讨会将与现有的推广计划相结合，以激发波士顿学院和爱荷华州立大学所服务社区的大学生和高中生对聚合物科学和催化的兴趣。从商品产品到特殊商品的合成聚合物处于现代社会的中心。在许多性质中，分子量、序列和分散性是决定聚合物材料性能的关键。因此，对这些性质的精确控制是现代合成聚合物化学的中心目标。这项研究将致力于通过将有机金属Ru催化剂限制在分子定义的笼子中来开发低应变环烯烃的过程开环歧化聚合(ROMP)。这种方法有望允许接触到单体分子，但阻止新生的聚合物链接触到这些受限催化剂。因此，可以从ROMP中获得定义良好的、高和超高相对分子质量、低分散性的聚合物。第一个目标将侧重于使用可逆孔开闭方法设计均匀和非均匀的锆基保持架。然后，这些笼子将被用来封装基于Ru的GRubbs和Hoveyda-GRubbs ROMP催化剂。第二个目标将利用分子受限催化剂，使包含可降解官能团的可持续发展导向的单体聚合成为可能。最后，系统地研究了分子受限催化剂介导的ROMP的动力学行为。与该项目相关的基本指导原则是一般性的，并有可能应用于各种其他催化剂介导链生长聚合技术，在这些技术中，需要控制终止和/或链转移事件。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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 Macromolecular, Supramolecular and Nanochemistry (MSN) program and the Chemical Catalysis (CAT) program in the Division of Chemistry, Jia Niu of Boston College and Wenyu Huang of Iowa State University are developing ring-opening metathesis polymerization (ROMP) catalyzed by organometallic ruthenium complexes confined within molecularly defined cages. Despite the significance of ROMP in producing a plethora of functional polymers, existing techniques still cannot completely prevent chain transfer and termination, in particular when low-strain monomers are involved. As a result, mixtures of linear and cyclic macromolecules of different sizes are formed that are difficult to separate. This research endeavors to directly address this unmet challenge and introduce a distinct strategy for processive ROMP. In this strategy, polymerization catalysts will be encapsulated in molecularly defined cage structures, such that, ideally only monomers, but not nascent polymers, can access the catalyst. This will thereby inhibit the chain transfer and termination caused by the interaction between the catalyst and the nascent polymer, resulting in linear macromolecules with controlled molecular weights. The developed methodology will also be applied to ROMP of sustainability-oriented monomers that are considered challenging for ROMP due to their low strain. These monomers include cyclic alkenes with low ceiling temperatures and those consisting of degradable functionalities. This research will provide interdisciplinary training for students in polymer synthesis and sustainability. The collaborative team will additionally develop a hybrid three-week summer workshop aimed to introduce polymer chemistry principles and practices into 3D-printing. The workshop will be integrated with existing outreach programs to stimulate interest in polymer science and catalysis among college and high school students in the communities served by Boston College and Iowa State University.Synthetic polymers ranging from commodity products to specialty goods are at the center of modern society. Among many properties, molecular weight, sequence, and dispersity are essential in determining the material performance of polymers. Therefore, the precise control over these properties is the central goal in modern synthetic polymer chemistry. This research will focus on developing processive ring-opening metathesis polymerization (ROMP) of low-strain cyclic alkenes through confining organometallic ruthenium catalysts into molecularly defined cages. Such an approach is expected to allow access to monomer molecules but prevent the nascent polymer chains from accessing these confined catalysts. As a result, well-defined, high, and ultra-high molecular weight, low dispersity polymers from ROMP could be realized. The first objective will focus on design of homogeneous and heterogeneous Zr-based cages using the reversable aperture opening/closing approach. These cages will then be utilized to encapsulate ruthenium-based Grubbs and Hoveyda-Grubbs ROMP catalysts. The second objective will leverage molecularly confined catalysts to enable polymerization of sustainability-oriented monomers containing degradable functionalities. Lastly, kinetic behaviors of ROMP mediated by molecularly confined catalysts will be systematically investigated. The basic guiding principles associated with this project are general and have the potential to be applied to various other catalyst-mediated chain-growth polymerization techniques in which the control of termination and/or chain-transfer events is desirable.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.