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

在化学学部大分子、超分子和纳米化学项目的资助下，德克萨斯农工大学的方磊教授和南密西西比大学的顾晓丹教授正在研究链的柔韧性如何影响共轭阶梯聚合物的物理性质。共轭聚合物是一类独特的非金属聚合物，具有类似于化学元素硅的半导体性质。当施加外部电压（如晶体管）或光照（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屏幕和其他利用电能转换为光的应用。另一方面，梯子聚合物是一种具有梯子连接的双链聚合物。这是通过四个化学键连接主聚合物链上的重复单元来实现的，而不是传统塑料中常见的两个化学键。在本研究中，合成了具有不同结构特征的共轭阶梯聚合物。控制聚合物是故意引入由小分子组成的骨干缺陷制备的。然后进行了详细的研究，将主链组成和长度与聚合物链的柔韧性联系起来。这些研究是通过使用中子和光散射技术来实现的，这些技术提供的精度范围从亚1纳米（人类头发直径的1/100,000）到远超过10微米（棉纤维的宽度）。这项工作所建立的相关性可能会为开发具有更好光学和电子性能的材料提供知识。教学创新解决了本科有机化学实验教学内容陈旧的问题。新设计的“诺贝尔奖反应”首先在两所大学实施，然后在国内和国际范围内传播。拓展活动使本科生和高中生了解现代化学研究。这项工作是专门为密西西比州大量代表性不足的少数民族和经济上处于不利地位的学生设计的。本研究的主要目的是建立刚性阶梯共轭聚合物的主链结构与链刚度之间的基本关系。该研究通过设计和合成具有不同结构特征的阶梯聚合物模型，并通过故意引入骨干缺陷进行控制，然后定量评估其链持久长度及其与结构特征的相关性。梯子聚合物模型和控制链的刚性是量化使用结合现代表征工具，重点是中子和光散射。研究还了解了链弯曲能对阶梯聚合物持续长度的影响。通过设计-综合-测量-设计循环，建立了结构-刚度的综合关联关系。与该奖项相关的结果有可能推进关于链刚性（或柔韧性）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 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.