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 cross-linked 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.