Molecular Control of Thermomechanics and Shape-Morphing of Dynamic Covalent Polymer Networks

Texas A&M Engineering Experiment Station, College Station TX

Investigators

Abstract

PART I: NON-TECHNICAL SUMMARY Shape-morphing polymers can transform the way these materials are used in everyday life as home and personal care products, including food packaging and sporting products. In response to a stimulus (such as temperature), these polymers can be repeatedly re-shaped without re-molding and re-used prior to the product’s end-of-life. Re-shapable polymers are also useful for soft robotics applications as they enable programming of the material motions via the use of a multi-material approach. The challenges are, however, to create materials with maximized ability for shape changes while controlling the morphing temperature and the materials’ self-healing characteristics. This project will take advantage of the capability of dynamic covalent bonds to dissociate and re-form, and the temperature-sensitivity of this process, to support controllable material shape morphing. The project will explore the effects of chemical substitutions at a dynamic bond and other molecular parameters of polymer materials (such as polymer chemical identity, number of dynamic bonds, etc.) on material functionality. Advanced instrumental techniques will be used to study the role of molecular motion in the material morphing and self-healing properties. The project will create a fertile training ground for participating graduate, undergraduate and high-school students. The PI will work with undergraduate students to provide research experiences and will be engaged in diversity-enhancing and outreach activities with the goal of encouraging female and minority students to pursue studies in materials science and careers in STEM fields. PART II: TECHNICAL SUMMARY The ability to make re-processable, re-shapable polymer materials can transform the future of commodity polymers and afford novel products for advanced biomedical and soft robotics applications. This project will study dynamic covalent polymer networks based on the maleimide-furan Diels-Alder (DA) reaction and aim to uncover the main underlying principles of developing materials with desired thermomechanical and shape-morphing characteristics. The focus will be on understanding how molecular and structural characteristics of the network determine the materials’ thermal, self-healing and shape-morphing properties. While the current DA polymer (DAP) materials made with 2-substituted furans (2-DAPs) suffer from low thermal stability, aging of their self-healing properties, and insufficient control of shape morphing, this project will address these challenges and develop a new family of DAP materials with practical thermal stability, self-healing and shape-morphing characteristics. This will be achieved by introducing stronger DA crosslinks (controlled by substitution in the furan ring) and understanding of the relationships between molecular parameters of the network (chain rigidity, length of the polymer strands, presence of entanglements), molecular motions and macroscopic viscoelastic properties of DAP materials. The project will involve synthesis of DAP networks using 3-substituted aminofurans (3-DAPs) with improved temperature resistivity, studies of stereochemistry and thermodynamics of DA junctions using DSC, FTIR, and NMR techniques, and exploration of the contributions of entanglements in material thermomechanical properties and self-healing properties using neutron reflectometry (NR) and fluorescence recovery after photobleaching techniques. The above studies will serve as a foundation for creating shape-morphing DAP constructs with programmable morphing of their permanent shape via the mechanism of network plasticity. The main outcome of the project will be the development of the knowledge relating molecular parameters, stereochemistry of DA crosslinks, molecular diffusivity within DAP networks, and the resultant material self-healing and shape morphing characteristics. . 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.