High-Performance Intrinsic Self-Healable Polymers: Rational Design, Evaluation Methods, and Applications

Self-healable polymers with rapid, room-temperature healing properties are especially attractive for various applications. Thus, systematic study of their structure-property relationship is demanded to obtain a better understanding of self-healing materials. The goal of this dissertation is to unravel the relationship between molecular structure, self-healing properties (healing rate and efficiency), and materials’ evaluation.

Controlling the H-bond density in a crosslinked poly(dimethyl siloxane) (PDMS) system allows to tailor their various physical properties and self-healing properties. In two studied systems, both the H-bond density and the chemical crosslink density were controlled individually, thus we can observe the impact of these two factors and elucidate the relationships on their chemical structure and fast, room-temperature self-healing properties. By precisely controlling the molar ratio between strong H-bond moiety and weak H-bond moiety, we obtained a series of self-healing materials with tunable rapid self-healing properties.

We aimed to develop self-healable polymers with high toughness since such material is not readily accessible today. We employed the thiourea structure to construct a resilient foundational component. PDMS was introduced to enhance the material's flexibility, the product exhibits high modulus and toughness, with switchable mechanical and healable properties under high humidity environment. Such polymer could perform fast room-temperature healing in an environment where humidity level is greater than 80%.

Moreover, a universal evaluation method for self-healing polymers is established and discussed, which is critical due to no available evaluation system currently. Through screening the key healing data (such as healing time and temperature) of a large quantity of published research, we revealed the trade-off between tensile strength and self-healing rate by constructing such evaluation method.

Finally, for future research perspectives, obtaining self-healing polymers with good performance from upcycled plastic waste to explore a better way to process plastic waste and lower the cost and carbon footprint of self-healing polymers. Poly(ethylene terephthalate) (PET) was selected as the original source for the upcycled self-healable polymer due to its accessibility and chemical versatility. After being deconstructed by aminolysis reaction, the deconstructed PET was transformed into self-healable polymers with tailored chemical structures.