Active Control of Sol-Gel-Sol Transitions of Aqueous Solutions of Doubly Responsive Hydrophilic Block Copolymers

由于自由流动溶液和自支撑凝胶之间的有趣转变以及结构和流变性能的相关变化，热敏嵌段共聚物胶束凝胶受到了相当大的关注，并已发现广泛的应用。本项目旨在开发一种策略，以主动控制双响应亲水性嵌段共聚物水溶液的溶胶-凝胶/凝胶-溶胶转变，并在不同的环境条件下实现溶胶-凝胶-溶胶转变的多个循环。本文将合成一系列对两种外界刺激都有响应的亲水性嵌段共聚物。生活？受控自由基聚合技术包括原子转移自由基聚合和可逆加成断裂链转移聚合。功能单体最近开发的PI？的实验室将被用来制备这些嵌段共聚物沿着与单体，其均聚物已被报道在水中表现出温敏性能。用转管法和流变仪绘制了这些嵌段共聚物水溶液在不同环境条件下的硬凝胶边界相图。胶束和胶束凝胶的结构将被阐明。将研究各种分子参数对溶胶-凝胶-溶胶转变的影响。在这项研究中，将采用各种表征技术，包括动态和静态光散射，流变仪，荧光光谱，小角X射线和中子散射，差示扫描量热法，透射电子显微镜。从这项研究中获得的知识将提供一个通用的原则，设计的多响应性水胶束凝胶技术的应用。非技术总结：从这项研究中开发的刺激响应性亲水嵌段共聚物在物质的受控包封和触发释放中具有潜在的应用（例如，药物分子）、组织工程、传感器和许多其他新兴技术。从这项工作中获得的知识将使多响应水凝胶的各种应用的合理设计。此外，该研究项目为研究生和本科生在定义明确的嵌段共聚物的合成，分子，胶束和分级自组装结构的表征，以及刺激响应软材料的设计方面的培训提供了强有力的设置。PI将继续努力为他所教授的高分子化学入门课程开发实验室组件。PI致力于帮助K-12教育中的科学教学。他将与当地高中教师和学生在他的实验室通过暑期项目，开发新的实验室实验高中化学课。

TECHNICAL SUMMARY:Owing to the intriguing transitions between free-flowing solutions and free-standing gels and the associated changes in structures and rheological properties, thermosensitive block copolymer micellar gels have received considerable attention and have found a wide range of applications. This project seeks to develop a strategy to actively control sol-gel/gel-sol transitions of aqueous solutions of doubly responsive hydrophilic block copolymers and to achieve multiple cycles of sol-gel-sol transitions under different environmental conditions. A series of hydrophilic block copolymers that can respond to two external stimuli will be synthesized by ?living?/controlled radical polymerization techniques including atom transfer radical polymerization and reversible addition fragmentation chain transfer polymerization. The functional monomers recently developed in the PI?s laboratory will be used to prepare these block copolymers along with monomers whose homopolymers have been reported to exhibit thermoresponsive properties in water. The hard gel boundary phase diagrams of aqueous solutions of these block copolymers under different environmental conditions will be mapped out by the tube inversion method and rheometry. The structures of micelles and micellar gels will be elucidated. The effects of various molecular parameters on the sol-gel-sol transitions will be investigated. A variety of characterization techniques will be employed in this research, including dynamic and static light scattering, rheometry, fluorescence spectroscopy, small angle X-ray and neutron scattering, differential scanning calorimetry, and transmission electron microscopy. The knowledge gained from this research will provide a general principle for design of multi-responsive aqueous micellar gels for technological applications. NON-TECHNICAL SUMMARY:The stimuli-responsive hydrophilic block copolymers developed from this research have potential applications in controlled encapsulation and triggered release of substances (e.g., drug molecules), tissue engineering, sensors, and many other emerging technologies. The knowledge gained from this work will enable rational design of multi-responsive aqueous gels for various applications. Moreover, this research project provides a strong setting for training of graduate and undergraduate students in the synthesis of well-defined block copolymers, characterization of molecular, micellar, and hierarchically self-assembled structures, and design of stimuli-responsive soft materials. The PI will continue his effort to develop a laboratory component for the introductory polymer chemistry course that he has been teaching. The PI is committed to help science teaching in K-12 education. He will work with local high school teachers and students in his laboratory through summer programs to develop new laboratory experiments for high school chemistry classes.