Kinetics of Polymer Interfacial Reactions

技术概要： 提出的研究的总体目标是发展的影响长链聚合物分子的界面反应的因素的基本理解。将聚合物接枝到表面是从生物传感器到空间稳定化的无数应用中的重要方面，在生物传感器中，生物大分子如DNA被束缚到基底以制备微阵列，在空间稳定化中，合成聚合物被束缚到表面以形成防止颗粒团聚的刷。深入了解这些界面接枝反应对于优化这些应用至关重要。为此，模型界面之间的“点击”反应与叠氮化物功能单层改性的基板和终止与炔基的聚合物进行了研究，通过红外光谱法，使用多次内反射技术，样品的叠氮化物吸收带的吸收反应后消失。叠氮化物和炔反应以形成三唑基团，由于其高产率和高化学选择性，该过程被称为“点击”化学。在界面处的溶液反应的动力学由拥挤效应介导，因为已经接枝的分子抑制另外的聚合物分子接近表面并与表面反应。因此，影响表面拥挤的因素正在调查中，包括溶剂的性质，聚合物分子量，表面官能团的密度，表面张力和聚合物表面相互作用的性质。功能性聚合物和叠氮化物功能性纳米颗粒之间的界面反应也通过透射红外光谱进行监测，以评估表面曲率的影响。界面熔融反应的研究是由本科生在一个平行的研究计划执行。收集的数据用于验证聚合物界面反应的理论处理。长链聚合物分子通常通过其末端连接到表面，以满足许多高科技工业应用的需求。例如，用于检测生物战剂或绘制基因组图谱的微阵列传感器是通过将天然生物聚合物如DNA、碳水化合物和蛋白质附着到硅晶片或微芯片的表面来制备的。聚合物刷，即通过其末端连接到固体基底的合成聚合物，用于无数应用中，包括胶体颗粒的稳定化、赋予药物递送载体生物隐形性以及在微流体装置中提供蛋白质抗性，仅举几例。所有这些应用的共同特征是需要将聚合物链的末端以受控的表面密度共价键合到感兴趣的基底上。这项研究计划的重点是对表面的聚合物反应以及影响它们的因素有一个基本的了解。两个互补的反应性官能团的反应速率对于溶液中的反应是很好理解的，然而，在表面处的反应速率并不完全理解，因为它们受到与表面的存在相关的许多物理和热力学参数的影响。聚合物表面反应的速率通过红外光谱技术进行研究，该技术可以定量和直接测量表面结合的反应性化学基团的反应速率，而不干扰反应的进展。研究的参数包括溶剂的性质（如果存在）、聚合物分子的大小、底层表面的性质和官能团的表面密度。这项研究所产生的知识将有助于工业产品的设计，从可以快速识别疾病的生物传感器到可以抵抗生物污染的设备。通过研究确定的基本原则被纳入PI教授的几门课程，包括大分子的物理化学和聚合物表面现象。从事该研究项目的本科生和博士生的多元化群体接受材料和表面科学方面的培训，了解知识产权如何受到保护，并学习如何向公众传达研究成果，这些技能在他们毕业后决定追求的任何领域都很重要。

TECHNICAL SUMMARY: The overall goal of the proposed research is to develop a fundamental understanding of the factors that influence interfacial reactions of long chain polymer molecules. The grafting of polymers to a surface is an important aspect in a myriad of applications ranging from biosensors, wherein bio macromolecules such as DNA are tethered to substrates to prepare microarrays, to steric stabilization, wherein a synthetic polymer is tethered to a surface to form a brush that prevents particle agglomeration. An intimate knowledge of these interfacial grafting reactions is essential to optimize these applications. Toward this end, model interfacial "click" reactions between a substrate modified with an azide function monolayer and a polymer terminated with an alkyne group are studied by infrared spectroscopy using a multiple internal reflection technique that samples the absorbance of the azide absorbance band which disappears upon reaction. Azides and alkynes react to form triazole groups in a process referred to as "click" chemistry due to its high yield and high chemoselectivity. The kinetics of solution reactions at interfaces are mediated by the effects of crowding as already grafted molecules inhibit additional polymer molecules from approaching and reacting to the surface. Factors that influence surface crowding are therefore under investigation including the nature of the solvent, the polymer molecular weight, the density of surface functional groups, the surface tension and the nature of polymer surface interactions. Interfacial reactions between the functional polymers and azide-functional nanoparticles are also monitored by transmission infrared spectroscopy in order to assess the effects of surface curvature. Interfacial melt reactions are investigated in a parallel program of research to be executed by undergraduates. The data collected are used to validate theoretical treatments of polymer interfacial reactions. NON-TECHNICAL SUMMARY:Long chain polymer molecules are often attached by their ends to a surface to meet the needs of many high-tech industrial applications. Microarray sensors, for example, used to detect biological warfare agents or to map genomes, are prepared by attaching natural biological polymers such as DNA, carbohydrates and proteins to the surface or a silicon wafer or microchip. Polymer brushes, synthetic polymers attached by their ends to solid substrates, are used in a myriad of applications including the stabilization of colloidal particles, imparting biological stealth to drug delivery vehicles and providing protein resistance in microfluidic devices to name but a few. The common feature in all of these applications is the need to covalently bond a polymer chain by its end to a substrate of interest at controlled surface density. The focus of this research proposal is to gain a fundamental understanding of such polymer reactions at surfaces and the factors that affect them. The rates of reactions of two complementary reactive functional groups are well understood for reactions in solution, however, the rates of reactions at surfaces, are not fully understood because they are influenced by a number of physical and thermodynamic parameters that are associated with the presence of a surface. The rates of polymer surface reactions are studied by an infrared spectroscopy technique that can quantitatively and directly measure the reaction rates of the surface bound reactive chemical group without disturbing the progress of the reaction. Parameters under investigation include the nature of the solvent if present, the size of the polymer molecule, the properties of the underlying surface, and the surface density of functional groups. The knowledge generated by this research will help in the design of industrial products ranging from biological sensors that can rapidly identify disease to devices that can resist biological fouling. The fundamental principles identified by the research are incorporated into several courses taught by the PI including the physical chemistry of macromolecules and polymer surface phenomenon. A diverse group of undergraduate and PhD students working on the research project receive training in materials and surface science, exposure to how intellectual property is protected, and learn how to communicate research results to the public, skills that are important in any field they decide to pursue after graduation.