Multifunctional dithiolane monomers for multi-scale, recyclable light-driven additive manufacturing

In this work, we develop a tetrafunctional monomer incorporating 1,2-dithiolanes as the reactive group, lipoic acid pentaerythritol ethoxylate, which is capable of photopolymerization and is suitable for light-based additive manufacturing with high spatial resolution across various length scales. This monomer polymerizes in either the presence or absence of exogenous photoinitiator. Using dynamic light processing and two photon lithography techniques, parts were printed on size scales ranging from multiple cm to μm, with resolution as small as 1 μm. As a result of the dithiolane polymerization, linear disulfides are formed, forming covalent adaptable networks directly from the polymerization reaction. Furthermore, through heating and dilution in solvent, the network was recycled back to the lipoic acid functional monomer with approximately 95% monomer recovery, which was subsequently repolymerized to achieve nearly identical modulus evolution as a function of exposure time. This work represents an advance in the development of multifunctional dithiolane monomers, as well as recyclable resins for additive manufacturing that are capable of polymerization with or without exogenous photoinitiators.