Chemical and Mechanical Tunability of 3D-Printed Dynamic Covalent Networks Based on Boronate Esters

• Published in: ACS macro letters 2021-07, Vol.10 (7), p.857-863
• Main Authors: Robinson, Lindsay L, Self, Jeffrey L, Fusi, Alexander D, Bates, Morgan W, Read de Alaniz, Javier, Hawker, Craig J, Bates, Christopher M, Sample, Caitlin S
• Format: Article
• Language: English
• Subjects: Esters; Materials Testing; Printing, Three-Dimensional; Resins, Plant
• ISSN: 2161-1653; 2161-1653
• DOI: 10.1021/acsmacrolett.1c00257

As the scope of additive manufacturing broadens, interest has developed in 3D-printed objects that are derived from recyclable resins with chemical and mechanical tunability. Dynamic covalent bonds have the potential to not only increase the sustainability of 3D-printed objects, but also serve as reactive sites for postprinting derivatization. In this study, we use boronate esters as a key building block for the development of catalyst-free, 3D-printing resins with the ability to undergo room-temperature exchange at the cross-linking sites. The orthogonality of boronate esters is exploited in fast-curing, oxygen-tolerant thiol–ene resins in which the dynamic character of 3D-printed objects can be modulated by the addition of a static, covalent cross-linker with no room-temperature bond exchange. This allows the mechanical properties of printed parts to be varied between those of a traditional thermoset and a vitrimer. Objects printed with a hybrid dynamic/static resin exhibit a balance of structural stability (residual stress = 18%) and rapid exchange (characteristic relaxation time = 7 s), allowing for interfacial welding and postprinting functionalization. Modulation of the cross-linking density postprinting is enabled by selective hydrolysis of the boronate esters to generate networks with swelling capacities tunable from 1.3 to 3.3.