Collaborative Research: Robust General Methods for Determination of Polyelectrolyte Molecular Weight and Polydispersity

在化学系的大分子、超分子和纳米化学（MSN）项目的支持下，拉尔夫·H。来自宾夕法尼亚州立大学的科尔比和路易斯A.弗吉尼亚理工学院和州立大学的Madsen正在开发测量聚电解质分子量的方法。 聚电解质是其重复单元含有电解质基团的长链大分子。 该基团在水中解离，使聚合物带电。 与盐类似，水溶液是导电的。 许多生物和人造高分子是聚电解质，并在生物医学，技术和工业科学中找到应用。 一些值得注意的例子包括植入涂层，控制药物输送，水净化系统，食品涂层和化妆品。 虽然有许多发达的技术用于准确测定中性聚合物的分子量，但离子或带电聚合物的方法相对较少。 主要原因是缺乏足够的理论方法来描述溶液中的非线性性质和非常复杂的行为。 本研究旨在为具有单一电荷类型（聚阴离子或聚阳离子）的离子聚合物（包括天然和合成体系）的分子量测定提供基础。 如果成功的话，这里开发的方法可以大大加速聚电解质的设计和合成。 此外，所提出的理论和实验方法的开发和验证预计将进一步影响聚合物科学的物理基础，并使人们能够对离子聚合物有新的认识。 这项工作也有望促进许多生物聚合物，如透明质酸，肝素，DNA和RNA的分子量的表征。 培训机会和接触高分子化学的概念和技术将提供给研究生和本科生在这两个机构。 研究活动也将被用来招募学生进入大分子计划，并为他们在聚合物科学的职业生涯做好准备。 弗吉尼亚理工大学的外联活动将包括突出离子聚合物凝胶、大分子链运动和能量储存概念的演讲。 这个动手K-12推广计划旨在拓宽思维，鼓励小学和高中学生考虑追求科学和技术的职业生涯。 宾夕法尼亚州立大学正在进行的REU（本科生研究经验）计划将被利用，包括从代表性不足的群体中招募学生。 聚电解质越来越多地用于替代能源技术、工程人体组织、药物输送和许多其他应用。聚电解质的广泛开发和应用的一个关键障碍在于表征其绝对分子量所需的极端努力。此外，沿着每条链的强静电排斥沿着与拉伸链的熵惩罚之间的平衡是微妙的，尚未详细了解，使得简单的模型只能在特定情况下工作。 该项目将侧重于详细的标度理论，在溶液中，基于四种不同的方法（使用测量的终端模量，弛豫时间，链扩散，相关长度和粘度）测量数均分子量（Mn）的行为。 这四种方法将采用溶液流变学，X射线散射和NMR扩散测量。 一个强烈的重点将放在开发一个工具箱，建立明确的操作策略和参数空间，这些方法的实际应用中的半稀释非纠缠制度。 测量范围将包括广泛的化学物质。 此外，正在开发一种通过NMR光谱法使用基于扩散的分子量测定方法可靠地量化聚电解质多分散性的技术。 最后，还将探讨中性聚合物分析方法的实用性。 如果成功，这项研究不仅将提供一个其他人可以使用的实验技术工具箱，而且还将提供一个理论框架，用于描述转化为分子量和多分散性的数据，该奖项反映了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支持。影响审查标准。

With the support of the Macromolecular, Supramolecular, and Nanochemistry (MSN) Program in the Division of Chemistry, Professors Ralph H. Colby from Pennsylvania State University and Louis A. Madsen from Virginia Polytechnic Institute and State University are developing methods for measuring the molecular weight of polyelectrolytes. Polyelectrolytes are long chain macromolecules whose repeating units contain an electrolyte group. This group dissociates in water, making the polymer charged. Similar to salts, polyelectrolyte solutions are electrically conductive. Many biological and artificial macromolecules are polyelectrolytes and find application in biomedical, technological and industrial science. Some notable examples include implant coatings, controlled drug delivery, water-purification systems, food coatings and cosmetics. While there are many developed techniques used to accurately determine the molecular weight of neutral polymers, methodologies for ionic or charged polymers are comparatively scarce. The principal reason is the lack of adequate theoretical approaches to describe polyelectrolyte properties and very complex behavior in solution. This research aims to provide a basis for molecular weight determination for ionic polymers having a single type of charge (polyanions or polycations), including both natural and synthetic systems. The methods being developed here, if successful, could significantly accelerate the design and synthesis of polyelectrolytes. Additionally, the development and validation of the proposed theoretical and experimental methods is expected to further impact the physical underpinnings of polymer science and enable new understanding of ionic polymers. This work also promises to facilitate the characterization of molecular weight for many biopolymers such as hyaluronic acid, heparin, DNA and RNA. Training opportunities and exposure to polymer chemistry concepts and techniques will be provided to graduate and undergraduate students at both institutions. Research activities will also be utilized to recruit students into macromolecular programs and prepare them for careers in polymer science. Outreach activities at Virginia Tech will include presentations that highlight concepts in ionic polymer gels, macromolecular chain motions and energy storage. This hands-on K-12 outreach program seeks to broaden thinking and encourage elementary and high school students to consider pursuing science and technology careers. The ongoing REU (research experiences for undergraduates) program at Pennsylvania State University will be leveraged to include recruitment of students from underrepresented groups. Polyelectrolytes are increasingly used in alternative energy technologies, engineered human tissues, drug delivery, and a host of other applications. A critical barrier to wider development and application of polyelectrolytes lies in the extreme effort required to characterize their absolute molecular weight. Furthermore, the balance between strong electrostatic repulsions along each chain with the entropic penalty for stretching the chain is delicate and not yet understood in detail, making simple models only work under specific circumstances. This project will focus on a detailed scaling theory for polyelectrolyte behaviors in solution that underlies four distinct methods (using measured terminal modulus, relaxation time, chain diffusion, correlation length, and viscosity) for measuring number-average molecular weight (Mn). These four methods will employ measurements by solution rheology, X-ray scattering, and NMR diffusometry. A strong emphasis will be placed on developing a toolbox that establishes well-defined operating strategies and parameter spaces for practical applications of these methods in the semi-dilute unentangled regime. The scope of measurements will include a wide array of polyelectrolyte chemistries. Furthermore, a technique to reliably quantify polydispersity for polyelectrolytes using the diffusion-based molecular weight determination method by NMR spectroscopy is under development. Lastly, the utility of the methods for analyzing neutral polymers will also be explored. If successful, this research will not only provide a toolbox of experimental techniques that others can use, but also a theoretical framework for scaling relationships to describe data that translate into molecular weight and polydispersity, parameters of critical importance in characterizing charged 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.