Thiol-Thioester Dynamic Covalent Chemistry in Polymer Networks

日常使用的合成聚合物有两大类。 热塑性塑料（通常简称为“塑料”）是通用的，可以熔化，溶解，重塑和回收。 相比之下，热固性材料通常是耐溶剂和耐热的较硬材料，但在其初始形成后通常不能再加工或回收。 科罗拉多大学的Christopher Bowman教授正在探索使用动态共价化学方法在这两种物质状态之间进行转换。 在如本文所实施的动态共价化学中，在施加所需刺激（例如暴露于光或热）后，化学键结构变得活化-以将一种类型的聚合物转化为另一种类型的方式重复地破坏和重整聚合物结构内的键。该项目研究聚合物结构与动态共价化学的内在方面之间的基本关系，包括反应性化学官能团，用于促进反应的催化剂，反应动力学和动态共价键的浓度。该项目研究合成和聚合物化学的基本现象以及应用科学的显著进步，同时为研究生和本科生提供深刻的教育经验。 此外，该项目培养了多样化的人才，包括大量的本科生和研究生，在化学合成，材料科学和高分子化学的独特组合。由NSF化学部门的大分子，超分子和纳米化学计划支持，鲍曼研究小组的目标是实现硫醇，硫酯交换反应作为交联聚合物网络中的可光活化和可光失活的动态共价化学。 该项目的重点是了解硫酯，催化剂和聚合物分子结构变化引起的化学结构-性质关系及其对共价键交换率的影响。对硫醇-硫酯交换反应及其在非极性、相对固定的环境中的催化动力学的基本理解使研究人员能够微调所需的键交换过程和相应的动态聚合物性质。各种外源递送刺激的组合（即，不同波长的光、热的添加或去除）用于控制网络内的化合物的活化，所述化合物催化硫醇侧基和硫酯交联之间的动态共价化学反应，并阻止与正交刺激的交换反应。具体而言，开发了用于启动和停止动态共价化学的基于光和热的刺激的双手柄。利用硫醇/硫酯交换反应，Bowman研究团队的目标是创造共价交联聚合物，这些聚合物能够从刚性热固性材料到可延展热塑性材料的用户导向的可逆转变，可应用于光学材料，增材制造，该奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的评估支持影响审查标准。

There are two broad categories of synthetic polymers familiar to everyday use. Thermoplastics (typically abbreviated simply as "plastics") are versatile and can be melted, dissolved, remolded and recycled. In contrast, thermosets are typically harder materials that are solvent and heat resistant and but cannot generally be reprocessed or recycled after their initial formation. Prof. Christopher Bowman at the University of Colorado is exploring the use of dynamic covalent chemistry approaches to transition between these two states of matter. In dynamic covalent chemistry as implemented here, upon application of a desired stimulus such as exposure to light or heat, chemical bond structures become activated - repeatedly breaking and reforming the bonds within the polymer structure in a manner that converts one type of polymer to the other. This project investigates the fundamental relationships between the polymer structure and the inherent aspects of the dynamic covalent chemistry including the reactive chemical functional group, the catalysts used to facilitate the reaction, the kinetics of the reaction, and the concentration of the dynamic covalent bond. This project investigates fundamental phenomena of synthetic and polymer chemistry as well as demonstrable advancement of applied science all while providing profound educational experiences for graduate and undergraduate students alike. Further, the project trains diverse personnel, comprising a large number of undergraduate and graduate students, in a unique combination of chemical synthesis, materials science, and polymer chemistry.Supported by the Macromolecular, Supramolecular and Nanochemistry Program of the NSF Chemistry Division, the Bowman research team aims to implement the thiol-thioester exchange reaction as a photoactivatable and photodeactivatable dynamic covalent chemistry in crosslinked polymer networks. The project focuses on understanding chemical structure-property relationships that arise with changes to the thioester, catalyst and polymer molecular structures and their impact on the covalent bond exchange rate. Fundamental understanding of the thiol-thioester exchange reaction and the kinetics of its catalysis in a non-polar, relatively immobile environment allows researchers to fine-tune the desired bond exchange process and the corresponding dynamic polymer properties. Combinations of various exogenously delivered stimuli (i.e., different wavelengths of light, addition or removal of heat) are used to control the activation of compounds within the network that catalyze the dynamic covalent chemistry between pendant thiol groups and thioester crosslinks and to arrest the exchange reaction with orthogonal stimuli. Specifically, dual handles of light and heat-based stimuli for starting and stopping the dynamic covalent chemistry are developed. Taking advantage of the thiol/thioester exchange reaction the Bowman research team aims to create covalently crosslinked polymers that are capable of user-directed, reversible transitions from rigid thermoset to malleable thermoplastic that has applications in optical materials, additive manufacturing, and adhesives.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.