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

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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.