CAREER: Photomodulation of Polymer Molecular Weight Distribution

凭借化学系高分子、超分子和纳米化学项目颁发的这一职业奖，纽约石溪大学的Melanie Chiu教授正在开发一种利用光来调节聚合物链端的化学反应来控制聚合物分散性的新方法。聚合物是由称为单体的小分子单位组成的长链，在我们的日常生活中一直存在，从工业生产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。这种聚合物的材料性质，包括硬度、熔融温度、电导率和降解曲线，往往受到聚合物的分散性或给定样品中分子链长的均匀程度的影响。控制聚合物的分散性--无论链的长度相似还是不同--是一种在不改变分子结构的情况下定制聚合物物理性质的有前途的方法。本研究正在开发一种聚合引发剂用光开启或关闭的一锅系统。这种光开关有两种状态：一种是产生低分散性聚合物，另一种是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分散性。研究项目的第二部分重点是系统地研究聚合物分散性对聚合物性能的影响。虽然这些努力侧重于特定类型的聚合物，聚乙烯醚，但最后的研究活动扩展了使用光来控制聚合物链端反应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对科学和工程的各个领域产生重大影响，在这些领域中，分子控制聚合物的性能是有意义的。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，以加强纽约州高中化学学生的教育。研究重点是建立一种光开关调节聚合物分散性的确定性方法，并通过光化学控制阳离子乙烯基醚聚合中链的繁殖速度与链端的失活，将其应用于嵌段共聚聚合物的合成。该项目的特点是开发光致变色Bronsted酸引发剂，在一种光致异构体状态下产生低分散性的聚合物，在另一种光致异构体状态下产生高分散性的聚合物。在第一个目标中，研究了在阳离子乙烯基醚聚合中，羧基二硫乙烯基乙烯实现光控制聚合物分散性的机理，并建立了一个全面的动力学模型来指导体系的进一步优化。第二个目标是羧基功能化二硫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控制链繁殖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的分散性的控制。这项工作中的化学扩大了可从外部调节的聚合反应参数的范围，并使人们能够更好地了解分散性如何影响聚合物性能。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 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.