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

Abstract

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.

4D-Printed Resins and Nanocomposites Thermally Stimulated by Conventional Heating and IR Radiation

“…In this regard, the processing of 3D-printable shape memory materials (SMMs), recently named 4D printing − (where the fourth dimension is time), is being explored. This technique allows the manufacturing of smart materials, whose programmed shape is finally deployed by an external stimulus. , Over the past 2 decades, SMMs based on metal alloys, ceramics, and polymers were developed.…”

Photoinduced Free Radical Promoted Cationic RAFT Polymerization toward “Living” 3D Printing

“…Their polymerization mechanisms can be divided into radical and cationic systems, which inherently determine the choice of monomers and thus determine the properties of the polymers. Recently, several “living” 3D printing systems have been reported based on reversible degenerative radical polymerization (RDRP) techniques for the fabrication of “living” polymeric products, which allow the postfunctionalization of 3D objects by reinitiation to introduce new monomers in a living manner. − These methods have shown great potential toward constructing stimuli-responsive, self-healing and various functional materials. However, some challenges and limitations urgently need to be addressed in this emerging field.…”

Recent Trends in Advanced Photoinitiators for Vat Photopolymerization 3D Printing

“…[65] Recently, Jin and co-workers explored the possibility of RAFT 3D printing under red LED light (635 nm, 0.5 mW cm −2 ) by introducing ZnTPP to the resin, with a disk-shaped model printed. [66] Meanwhile, Zhu and co-workers attempted cationic RAFT polymerization toward NIR light 3D printing by using a commercially available iron catalyst, cyclopentadienyl iron dicarbonyl dimer (Fe 2 (Cp) 2 (CO) 4 ) as the photocatalyst. [67] Although further optimization is required, photomediated RAFT system [45] has broadened the scope of additive manufacturing in a living manner.…”