Living Polymer Networks Based on a RAFT Cross-Linker: Toward 3D and 4D Printing Applications

Controlled modification in the structure and properties of three-dimensional (3D) printed polymers, as in the broader context of crosslinked polymer networks, in response to an external stimulus has been of great importance to meet the demands of advanced applications and environmental sustainability concerns. In this study, a dynamic covalent di(meth)acrylate cross-linker containing a reversible addition-fragmentation chain transfer (RAFT) trithiocarbonate (TTC) functionality was synthesized and used for the formation of living photoexpandable/transformable polymer networks (PET-PNs). The network-bound TTC functionalities were activated in a postsynthesis stage via a visible light-controlled photoredox-catalyzed RAFT polymerization, enabling monomer addition into the existing scaffolds. This approach allowed controllable and successive postsynthesis photogrowth, photofunctionalization, and/or photowelding reactions. The expandable RAFT-capable TTC cross-linker (TTC-XL) was also exploited to manufacture living 3D materials via a layer-by-layer photopolymerization process facilitated by a modified digital light processing (DLP) 3D printer. The 3D printed materials were also capable of undergoing successive postprinting reactions (e.g. functionalization) via a photoredox-catalyzed RAFT process under a red light-emitting diode (LED) light irradiation. From the viewpoint of material sustainability and recyclability, this study is a great step forward and it will open up additional possibilities in the field of 3D printing for the fabrication of advanced functional materials.