Polymer Networks Containing Reversibly Associating Side-Groups

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This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).TECHNICAL SUMMARY: This research involves the design, synthesis, and study of network polymers containing highly selective, multiple hydrogen-bonding side-groups. The major research goal is to understand how reversible binding affects the material?s rate-of-strain and mass transport kinetics. Shape memory polymers (SMPs) will be developed that 1) are transparent to light at all processing temperatures, 2) exhibit amorphous or rubbery low-temperature states, and 3) enable precise tuning of shape recovery temperatures and rates. Preliminary studies have shown that lightly crosslinked elastomers containing reversibly associating side-groups exhibit shape-memory effects with a unique temperature-dependent shape-recovery. Planned research builds on these findings through the synthesis of well-defined elastomers involving uncrosslinked (linear) polymer precursors. Living free radical polymerization of poly(acrylates) will be performed to systematically vary architectural parameters including a) covalent crosslink density, b) associating side-group content, c) side-group spacer length, and d) the type and strength of H-bonding side-group. Synthesized polymers and networks will be studied in solution and in the melt to elucidate mechanistic details that influence shape memory responses. Research will pave the way to develop new features including two-stage shape responses, light and magnetic field triggered responses, and recyclable shape-memory materials. Research will also examine how reversible hydrogen-bonding affect mass transport. Diffusion of small molecules through synthesized networks will be studied using a custom-built permeation apparatus as well as multiphoton fluorescence recovery after photobleaching (MP-FRAP) techniques. The research plan provides a springboard for the PI to investigate biomedical devices including intraocular lenses, spinal disk prosthetics, and drug delivery platforms.NON-TECHNICAL SUMMARY: The principle investigator?s laboratory has recently developed novel shape-memory elastomers that use strong, reversible hydrogen-bonding groups to modify mechanical properties. The described study is to systematically vary the material architecture to fundamentally understand how reversible association affects time-scales of mechanical deformation and mass transport. The resulting knowledge will establish clear material design principles to foster new technologies including shape memory polymers, thermoplastic elastomers, and self-healing materials. Material responsiveness may also be exploited to engineer drug delivery devices and soft-tissue prosthetics designed for minimally invasive surgery. Educational aims are closely tied to research objectives. Graduate and undergraduate students will acquire research skills including polymer synthesis, rheology, transport studies, and thermal mechanical analysis. The research described is synergistic with a new course, ?Engineering of Soft Matter?, which introduces students to this emerging field. In addition, the PI will further develop the education outreach program "Green Engineering" to provide professional development opportunities to high school teachers. This program strengthens connections between secondary education teachers and the technical workforce by offering hands-on teaching workshops. There, high school teachers learn and discuss emerging ?green? technologies including energy conservation, photovoltaics, and fuel cells.