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

技术摘要：由于自由流动溶液和独立凝胶之间有趣的转变，以及与之相关的结构和流变性的变化，温敏嵌段共聚胶束凝胶受到了极大的关注，并得到了广泛的应用。该项目旨在开发一种策略，以积极控制双响应性亲水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多个循环的溶胶-凝胶-溶胶转变。通过原子转移自由基聚合和可逆加成断裂链转移聚合等活性/可控自由基聚合技术，合成了一系列对两种外界刺激都有响应的亲水性嵌段共聚物。最近在皮？S实验室开发的功能单体将用于制备这些嵌段共聚物，以及据报道其均聚物在水中表现出温度响应性的单体。用管倒置法和流变法绘制了不同环境条件下嵌段共聚物水溶液的硬凝胶界面相图。胶束和胶束凝胶的结构将被阐明。研究了各种分子参数对Sol-Gel-Sol转变的影响。本研究将使用多种表征技术，包括动态和静态光散射、流变学、荧光光谱、小角X射线和中子散射、差示扫描量热法和透射电子显微镜。这项研究所获得的知识将为设计技术应用的多响应水胶束凝胶提供一般原则。非技术综述：本研究开发的刺激响应型亲水嵌段共聚物在物质(如药物分子)的受控包裹和触发释放、组织工程、传感器和许多其他新兴技术中具有潜在的应用前景。从这项工作中获得的知识将使合理设计适用于各种应用的多响应水凝胶。此外，该研究项目为研究生和本科生提供了一个强有力的培训环境，使他们能够合成定义明确的嵌段共聚物，表征分子、胶束和分级自组装结构，以及设计对刺激响应的软材料。PI将继续努力为他一直教授的聚合物化学入门课程开发实验室组件。该协会致力于帮助K-12教育中的科学教学。他将通过暑期项目与实验室里的当地高中教师和学生合作，为高中化学课开发新的实验室实验。

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.