Initiation Strategies From Common Functional Groups in Photocontrolled Polymerizations

在化学系大分子、超分子和纳米化学项目的支持下，康奈尔大学的Brett P. Fors正在开发从普通化学官能团开始的引发策略，以制备具有可控结构的聚合物。聚合物，或由单体衍生的重复单元组成的长链，是我们日常生活中必不可少的，而且无处不在。我们在工业制造的塑料、植物中天然存在的纤维素，甚至是棉花等植物衍生材料中都会遇到它们。控制聚合已经彻底改变了科学界制造聚合材料的方式，使合成定义明确的大分子成为可能，而大分子的大小和功能可以精确定制。然而，从小分子、生物分子或其他聚合物中可控地接枝聚合物，需要在这些分子上合成起始物质。这通常涉及繁琐的多步骤合成，效率低下，而且往往是人们可以获得的塑料的限制因素。本研究将利用光催化直接引发常见官能团的自由基聚合。具体地说，将开发和研究直接从氢化C-H键或羧酸接枝的聚合过程。从C-H键接枝聚合物的能力将为规避预功能化提供机会，为聚合物升级回收和表面改性提供机会。羧酸引发聚合物将为控制和直接的位点选择性形成蛋白质-聚合物偶联物开辟一条途径，在蛋白质治疗中具有潜在的应用价值。此外，还研究了用简单的硝基烷烃引发剂进行光控自由基聚合的方法。硝基烷烃对聚合物链端施加独特的反应性，允许自由基和阴离子过程配对，使接枝聚合物定义明确。综上所述，本研究的引发策略有望为高级功能聚合物的合成提供新的途径。这项工作将为纽约伊萨卡的学生提供大量的培训机会，代表了聚合物化学和光催化之间的交叉授粉。它将扩大现有的教育推广活动，包括虚拟实验室参观和聚合物科学教程视频。这些方法将向全国各地的学校分发高质量的远程STEM（科学、技术、工程和数学）教材，并将研究的影响从科学界扩展到普通公众。本研究将集中于光控聚合中常见官能团引发策略的发展。在第一个目标中，将开发由水合C-H键选择性引发的光控自由基聚合，以避免引发剂合成的挑战，并使功能聚合物的流线型形成。模型研究将包括二氧六烷作为氢原子源和丙烯酸甲酯作为单体的可逆加成-破碎链转移（RAFT）聚合。在第二个目标中，该方法将扩展到羧酸基引发剂。重点将放在理解催化循环，包括氧化脱羧和链盖步骤和RAFT平衡的位置。最后，硝基烷烃引发剂将探索替代常规使用的烷基溴在原子转移自由基聚合（ATRP）。这种新的链端功能化方法将利用硝基烷烃的可逆裂解裂解生成烷基自由基和相应的亚硝酸盐阴离子。这项工作代表了一种重要的新方法来控制聚合的开始，具有直接接枝聚合物的潜力，从大量的商品，专业，宏观和生物分子，而不需要预功能化。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 Macromolecular, Supramolecular, and Nanochemistry program in the Division of Chemistry, Brett P. Fors of Cornell University is developing initiation strategies from common chemical functional groups to prepare polymers with controlled structures. Polymers, or long chains consisting of repeating units derived from monomers, are essential and ever-present in our everyday lives. We encounter them in industrially manufactured plastics, naturally occurring cellulose in plants, and even plant-derived materials like cotton. Controlled polymerizations have revolutionized the way the scientific community makes polymeric materials, enabling the synthesis of well-defined macromolecules in which the size and functionality can be precisely tailored. However, controllably grafting polymers from small molecules, biomolecules, or other polymers, requires the synthesis of initiating species on those molecules. This typically involves tedious multistep syntheses that are inefficient and often the limiting factor in the plastics that one can access. This research will utilize photocatalysis to directly initiate radical polymerizations from common functional groups. Specifically, polymerization processes that are directly grafted from either hydridic C–H bonds or carboxylic acids will be developed and studied. The ability to graft polymers from C–H bonds will offer an opportunity to circumvent pre-functionalization, holding opportunities in polymer upcycling and surface modification. Polymer initiation from carboxylic acids will open an avenue to controlled and direct site-selective formation of protein-polymer conjugates for potential applications in protein therapeutics. Additionally, a photocontrolled radical polymerization using a simple nitroalkane initiator will be examined. The nitroalkane imposes unique reactivity on the polymer chain end, allowing the pairing of radical and anionic processes to make well-defined graft polymers. Overall, the initiation strategies in this research are expected to provide new avenues for the synthesis of advanced functional polymers. This work will offer a substantial training opportunity for students in Ithaca, New York that represents a cross-pollination between polymer chemistry and photocatalysis. It will expand the existing educational outreach activities to include virtual laboratory tours and polymer science tutorial videos. These approaches will distribute high-quality remote STEM (science, technology, engineering and mathematics) educational materials to schools across the country and extend the impact of the research beyond the scientific community to the general public.This research will focus on the development of initiation strategies from common functional groups in photocontrolled polymerizations. In the first objective, photocontrolled radical polymerizations initiated selectively from hydridic C-H bonds will be developed to circumvent challenges of initiator synthesis and enable the streamlined formation of functional polymers. Model studies will include dioxane as the hydrogen-atom source and methyl acrylate as the monomer in reversible addition-fragmentation chain-transfer (RAFT) polymerization. In the second objective, the methodology will be extended to carboxylic acid-based initiators. Strong emphasis will be placed on understanding the catalytic cycle including the oxidative decarboxylation and chain capping steps and the position of RAFT equilibrium. Lastly, nitroalkane initiators will be explored as alternatives to conventionally used alkyl bromides in atom transfer radical polymerization (ATRP). This approach to new chain-end functionality will take advantage of reversible mesolytic cleavage of a nitroalkane to generate an alkyl radical and corresponding nitrite anions. This work represents an important new approach to the initiation of controlled polymerizations, with the potential to directly graft polymers from a vast array of commodity, specialty, macro, and biological molecules without pre-functionalization.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.