Collaborative Research: Synthesis and Rigidity Quantification of Ladder Polymers with Controlled Structural Defects

在化学系大分子、超分子和纳米化学项目的资助下，德克萨斯农工大学的雷方教授和南密西西比大学的顾晓丹教授正在研究链柔性如何影响共轭梯形聚合物的物理性质。共轭聚合物是一类独特的非金属聚合物，其半导体性质类似于化学元素硅。当外加电压(如晶体管)或光线照射(如光伏电池)时，这些长链碳基分子可以导电。共轭聚合物广泛应用于太阳能电池、LED屏幕和其他利用电光转换的应用。另一方面，梯形聚合物是一种具有梯形连接性的双链聚合物。这是通过将主聚合物链上的重复单元通过四个化学键相互连接来实现的，而不是传统塑料中通常看到的两个键。本研究合成了具有不同结构特征的共轭梯形聚合物。控制聚合物是用故意引入的由小分子组成的主链缺陷制备的。然后进行详细的研究，以将主干组成和长度与聚合物链的柔性相关联。这些研究是通过使用中子和光散射技术实现的，这些技术提供的长度范围从不到1纳米(人类头发直径的1/10万)到远远超过10微米(棉纤维的宽度)。通过这项工作建立的相关性可能会为开发具有更好的光学和电子性能的材料提供知识。教育创新解决了本科有机化学实验课内容陈旧的问题。新设计的“诺贝尔奖反应”首先在两所大学实施，然后在全国和国际范围内传播。外展活动使本科生和高中生接触到现代化学研究。这项工作是专门为密西西比州代表不足的少数族裔和经济困难的学生而设计的。这项研究的主要目标是建立刚性梯形共轭聚合物的主链组成和链刚性之间的基本关联。这项研究是通过设计和合成具有不同结构特征的模型梯形聚合物来进行的，并以故意引入的主链缺陷为对照，然后对它们的链持续长度及其与结构特征的相关性进行定量评估。梯形聚合物模型和控制的链刚性是使用组合的现代表征工具来量化的，重点是中子和光散射。还研究了链弯曲能对梯形聚合物驻留长度的影响。通过迭代设计-综合-测量-设计循环，建立了结构-刚度综合关联式。与该奖项相关的结果有可能提高关于链刚性(或柔性)如何决定各种聚合物的基本性质和实际应用的知识。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 funding from the Macromolecular, Supramolecular and Nanochemistry Program of the Chemistry Division, Professors Lei Fang of Texas A&M University and Xiaodan Gu of University of Southern Mississippi are investigating how chain flexibility influences the physical properties of conjugated ladder polymers. Conjugated polymers are a unique class of non-metallic polymers with semiconducting properties resembling that of the chemical element silicon. These long chain carbon-based molecules can become conductive when external voltage is applied (like in transistors) or light shines on them (like in photovoltaic cells). Conjugated polymers are extensively used in solar cells, LED screens and other applications that utilize the conversion of electricity to light. Ladder polymers, on the other hand, are a type of double stranded polymers with the connectivity of a ladder. This is achieved by interconnecting repeating units along the main polymer chain by four chemical bonds, instead of the two bonds typically seen in conventional plastics. In this research, conjugated ladder polymers with varied structural features are synthesized. Control polymers are prepared with deliberately introduced backbone defects that consist of small molecules. Detailed studies are then conducted to correlate backbone composition and length with the flexibility of the polymer chains. These studies are enabled by employing neutron and light scattering techniques which provide accuracy at lengths ranging from sub 1 nanometer (1/100,000 of human hair diameter) to well beyond 10 micrometers (the width of cotton fiber). Correlations established as a result of this work may provide knowledge that could lead to the development of materials with better optical and electronic performance. Educational innovation tackles the problems associated with outdated contents in undergraduate organic chemistry laboratory courses. The newly designed “Nobel Prize Reactions” are first implemented at both universities and then disseminated at national and international scales. Outreach activities expose undergraduate and high school students to modern chemical research. This work is specifically designed to benefit a large number of underrepresented minorities and economically disadvantaged students in Mississippi.The primary goal of this research is to establish the fundamental correlations between backbone constitution and the chain rigidity for rigid ladder conjugated polymers. The research is conducted through the design and synthesis of model ladder polymers with varied structural features, and controls with deliberately introduced backbone defects, followed by quantitative evaluation of their chain persistence length and correlation with structural features. Chain rigidity of the ladder polymer models and controls is quantified using combined modern characterization tools with an emphasis on neutron and light scattering. Studies are also performed to understand the influence of chain bending energy on persistent length for ladder polymers. Comprehensive structural-rigidity correlation through iterative design-synthesis-measurement-design cycles is established. Results associated with this award have the potential to advance knowledge on how the chain rigidity (or flexibility) determines the fundamental properties and practical applications of a wide range of polymers.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.