CAREER: Photomodulation of Polymer Molecular Weight Distribution

纽约石溪大学的Melanie Chiu教授获得了化学学部大分子、超分子和纳米化学项目颁发的CAREER奖，她正在开发一种利用光介导聚合物链末端的化学反应性来控制聚合物分散性的新方法。聚合物，一种被称为单体的小分子单位长链，在我们的日常生活中是必不可少的，无处不在，从工业制造的塑料，到植物中天然存在的纤维素和植物衍生材料，如棉花。这种聚合物的材料特性，包括刚度、熔化温度、电导率和降解特性，通常受到聚合物的分散性或给定样品中分子链长度均匀性的影响。控制聚合物的分散性——无论链的长度是相似的还是不同的——是一种很有前途的方法，可以在不改变聚合物分子结构的情况下调整聚合物的物理性质。本研究正在开发一种单锅系统，在该系统中，聚合引发剂通过光来开启或关闭。这种光开关产生两种状态：一种产生低分散性聚合物，另一种产生高分散性聚合物。一旦这些聚合物被制造出来，该研究项目的特点是研究不同的反应参数如何影响可获得的最佳分散性。研究项目的第二部分侧重于系统研究聚合物分散性对聚合物性能的影响。虽然这些努力集中在特定类型的聚合物，聚乙烯醇醚上，但最后一项研究活动扩展了使用光来控制聚合物链端反应性以形成其他类型聚合物的概念。与该奖项相关的结果有可能显著影响科学和工程的各个领域，这些领域对聚合物性质的分子控制感兴趣。赵教授通过与纽约州化学硕士教师计划合作开发课程材料，促进研究和教育的整合，以提高整个纽约州高中化学学生的教育。本研究的重点是建立一种确定的光开关调节聚合物分散性的方法，并将其应用于嵌段共聚物合成中，通过光化学方法控制控制阳离子乙烯醚聚合中链的传播速率和链端的失活速率。该项目的特点是开发光致变色Bronsted酸引发剂，该引发剂产生的聚合物在一种光异构状态下具有低分散性，而在另一种光异构状态下具有高分散性。在第一个目标中，研究了羧基功能化二乙烯基在阳离子乙烯醚聚合过程中光控聚合物分散性的机理，并建立了综合动力学模型，指导系统的进一步优化。二是羧基功能化二乙烯引发剂在嵌段共聚物合成中的应用及其材料性能的研究。最终目标扩展了外部操纵链传播和链端失活的相对速率的概念，以实现对其他类型受控聚合反应中分散性的控制。这项工作中的化学扩展了聚合反应参数的范围，这些参数可以外部调节，并且可以更好地理解分散性如何影响聚合物的性质。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 this CAREER Award from the Macromolecular, Supramolecular and Nanochemistry Program in the Chemistry Division, Professor Melanie Chiu at Stony Brook University in New York is developing a new method for controlling polymer dispersity using light to mediate the chemical reactivity of polymer chain-ends. Polymers, long chains of small molecular units called monomers, are essential and ever-present in our everyday lives, from industrially-manufactured plastics, to naturally occurring cellulose in plants and plant-derived materials, like cotton. The material properties of such polymers, including stiffness, melting temperature, electrical conductivity, and degradation profile are often affected by the polymer’s dispersity, or the uniformity of the molecular chain lengths within a given sample. Controlling polymer dispersity—whether the chains are of similar or dissimilar lengths—is a promising means of tailoring a polymer’s physical properties without changing its molecular structure. This research is developing a one-pot system in which the polymerization initiator is turned on or off with light. This photo-switch results in two states: one that yields low dispersity polymers and another one that yields high dispersity polymers. Once these polymers are made, the research project features studies on how different reaction parameters affect optimize the dispersities that can be accessed. The second part of the research project focuses on systematically studying how polymer dispersity affects polymer properties. While these efforts focus on specific types of polymers, polyvinyl ethers, the last research activity expands the concept of using light to control polymer chain-end reactivity to form other types of polymers. Results associated with this award have the potential to significantly impact various fields of science and engineering where molecular control over polymer properties is of interest. Professor Chiu fosters integration of research and education by developing curriculum materials in collaboration with the New York State Master Chemistry Teacher's program to enhance the education of high school chemistry students throughout New York State.The research is focused on establishing a deterministic method for photoswitchable regulation of polymer dispersity and its applications to block copolymer synthesis by photochemically manipulating the rate of chain propagation versus deactivation of the chain-end in controlled cationic vinyl ether polymerizations. The project features the development of photochromic Bronsted acid initiators that yield polymers with low dispersity in one photoisomeric state, and high dispersity in the other photoisomeric state. In the first objective, the mechanism by which the carboxy-functionalized dithienylethenes enable photocontrol over polymer dispersity in cationic vinyl ether polymerizations is studied, and a comprehensive kinetic model is constructed to guide further optimization of the system. The second objective focuses on the application of the carboxy-functionalized dithienylethene initiators to the synthesis of block copolymers and investigation of their materials properties. The final objective expands the concept of externally manipulating relative rates of chain propagation and chain-end deactivation to achieve control over dispersity in other types of controlled polymerization reactions. The chemistry in this work expands the repertoire of polymerization reaction parameters that can be externally modulated and enables a better understanding of how dispersity influences polymer properties.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.