A Versatile 3D and 4D Printing System through Photocontrolled RAFT Polymerization

Abstract

Reversible addition‐fragmentation chain‐transfer (RAFT) polymerization is a valuable tool for synthesizing macromolecules with controlled topologies and diverse chemical functionalities. However, the application of RAFT polymerization to additive‐manufacturing processes has been prevented due to the slow polymerization rates of typical systems. In this work, we developed and optimized a rapid visible (green) light mediated RAFT polymerization process and applied it to an open‐air 3D printing system. The reaction components are non‐toxic, metal free and environmentally friendly, which tailors these systems toward biomaterial fabrication. The inclusion of RAFT agent in the photosensitive resin provided control over the mechanical properties of 3D printed materials and allowed these materials to be post‐functionalized after 3D printing. Additionally, photoinduced spatiotemporal control of the network structure provided a one‐pass approach to 4D printed materials. This RAFT‐mediated 3D and 4D printing process should provide access to a range of new functional and stimuli‐responsive materials.

Recent Advances on Copper Complexes as Visible Light Photoinitiators and (Photo) Redox Initiators of Polymerization

“…To avoid the formation of the less reactive ROO• radicals, introduction of a reductant that could reduce Cu (II) into Cu (I) was introduced, favoring Equation (6) over Equation (7). To optimize the initiating system and mutualize as much as possible the different additives used for both the redox and the photochemical mechanisms, the reductant used for the redox system can also be the same as that used in the photochemical mechanism.…”

“…Parallel to the photoinitiated process, redox potentials of Cu-4 are also adapted to induce redox reactions with peroxides such as R'OOH so that R'O• and R'OO• radicals can be simultaneously generated in situ by redox reactions with Cu-4 (II) and Cu-4 (I) (see Equations (6) and 7 To avoid the formation of the less reactive ROO• radicals, introduction of a reductant that could reduce Cu (II) into Cu (I) was introduced, favoring Equation (6) over Equation (7). To optimize the initiating system and mutualize as much as possible the different additives used for both the redox and the photochemical mechanisms, the reductant used for the redox system can also be the same as that used in the photochemical mechanism.…”

“…Additionally, no work-up subsequent to the polymerization process is required so that the polymer pieces obtained by photopolymerization are ready to use. This unique ability to provide polymeric materials that can be immediately used after polymerization is nowadays valuated in the emerging 3D and 4D printing technologies [7][8][9][10]. In contrast with the traditional thermal polymerization, which require hours to form polymers, by photopolymerization, not only high polymerization rates, but also high final monomer conversions can be obtained within a few minutes.…”

Visible-Light-Curable Solvent-Free Acrylic Pressure-Sensitive Adhesives via Photoredox-Mediated Radical Polymerization

“…Since most photocatalysts (PCs) exhibit sufficient visible-light absorption, photocatalyzed polymerization can be conducted under low-energy visible light irradiation conditions using sunlight and light-emitting diodes (LEDs) as light sources [ 12 , 13 ], which are safer for humans than UV light. Visible light-absorbing PCs have been widely used for numerous light-driven photocatalyzed radical polymerization reactions, including photocatalyzed free radical polymerization [ 14 , 15 , 16 ], photoinduced electron/energy transfer–reversible addition-fragmentation chain transfer [ 17 , 18 , 19 , 20 ], and photoredox-mediated atom transfer radical polymerization (ATRP) [ 21 , 22 , 23 , 24 ], which can used for a wide range of applications, such as 3D/4D printing [ 25 , 26 , 27 , 28 ], biosystems [ 28 , 29 , 30 ], hydrogels [ 28 , 29 , 31 , 32 , 33 ], dental materials [ 34 , 35 , 36 ], and coatings [ 37 , 38 ].…”

The Fabrication of Micro Beam from Photopolymer by Digital Light Processing 3D Printing Technology

“…3D printing technology has become progressively popular in the fabrication of MEMS, since it can be employed to manufacture complicated structures clearly from digital files, for instance computer-assisted design drawings. This technology helps to improve the design and production and especially facilitates the production and repair of complex parts using printing through layer-by-layer deposition of the constituent materials [21][22][23]. With the progress of 3D printing techniques, interest in using 3D printing for building MEMS systems has grown remarkably in the areas of biomedical, electronics, wearable devices, soft robots, and automotive applications [24][25][26][27][28][29].…”