Weldable and Reprocessable Shape Memory Epoxy Vitrimer Enabled by Controlled Formulation for Extrusion-Based 4D Printing Applications

Vitrimers are attracting attention owing to their cross-linked polymer architecture with reprocessability based on an associative covalent adaptable network (CAN). To expand their field of application, intensive research is being conducted to control the properties of vitrimers. Herein, the properties of vitrimers are tuned to render these materials extrudable and weldable. The engineered vitrimer is utilized as a functional "ink" for fused filament fabrication (FFF) 4D printing. The rheological properties of the vitrimers are adjusted by changing the chemical formulation without the use of special chemicals, additional reactions, or unique processes. Using the intrinsic cross-linked architecture of the vitrimers, shape memory performance is demonstrated and used in 4D printing applications. A bond exchange reaction involving transesterification leads to the topological rearrangement of vitrimers, thus allowing them to be reprocessed, reshaped, recycled, and reprinted. In addition, heterogeneous materials in the form of an epoxy vitrimer and ester-containing polylactic acid (PLA) are joined using direct interfacial welding. This study suggests a simple approach to customize the characteristics of vitrimers to confer special properties (shape memory) upon conventionally printed 3D objects, which could be used for soft robot fabrication, the assembly of materials, and multifunctional composites.