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正在开发从常见化学官能团制备具有受控结构的聚合物的引发策略。 聚合物，或由单体衍生的重复单元组成的长链，在我们的日常生活中是必不可少的。 我们在工业制造的塑料，植物中天然存在的纤维素，甚至棉花等植物衍生材料中都会遇到它们。 可控聚合已经彻底改变了科学界制造聚合物材料的方式，使得能够合成定义明确的大分子，其中大小和功能可以精确定制。然而，可控地从小分子、生物分子或其它聚合物接枝聚合物需要在那些分子上合成引发物质。 这通常涉及繁琐的多步合成，效率低下，并且通常是人们可以获得的塑料的限制因素。本研究将利用双氢呋喃直接引发常见官能团的自由基聚合。具体地说，将开发和研究直接接枝自双碳氢键或羧酸的聚合工艺。 从C-H键接枝聚合物的能力将提供规避预官能化的机会，在聚合物升级循环和表面改性中保持机会。 从羧酸引发聚合物将开辟一条途径，以控制和直接的位点选择性形成蛋白质-聚合物缀合物的蛋白质治疗的潜在应用。此外，使用简单的硝基烷烃引发剂的光控自由基聚合将被检查。 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的配对，以制造明确定义的接枝聚合物。 总之，本研究中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，这代表了聚合物化学和聚合物之间的交叉授粉。 它将扩大现有的教育推广活动，包括虚拟实验室图尔斯参观和聚合物科学辅导录像。 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大到普通公众。这项研究将侧重于开发光控聚合中常见官能团的引发策略。 在第一个目标，光控自由基聚合引发的选择性从双碳-氢键将开发规避引发剂合成的挑战，并使流线型的功能聚合物的形成。 模型研究将包括二氧六环作为氢原子源和丙烯酸甲酯作为可逆加成-断裂链转移（RAFT）聚合中的单体。 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，包括氧化脱羧和链封端步骤和RAFT平衡的位置。 最后，硝基烷烃引发剂将被探索作为原子转移自由基聚合（ATRP）中常规使用的烷基溴的替代品。这种新的链端官能度的方法将利用硝基烷烃的可逆介晶裂解产生烷基自由基和相应的亚硝酸根阴离子。 这项工作代表了一个重要的新方法，以启动控制聚合，有可能直接接枝聚合物从大量的商品，专业，宏观和生物分子没有prefunctionalization.This奖项反映了NSF的法定使命，并已被认为是值得通过评估使用基金会的智力价值和更广泛的影响审查标准的支持。

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.