Oxygen Tolerant PET-RAFT Facilitated 3D Printing of Polymeric Materials under Visible LEDs

Abstract

The photopolymerization-based 3D printing process is typically conducted by using free radical polymerization, which leads to fabrication of immutable materials. An alternative 3D printing of polymeric materials by using trithiocarbonate (TTC) reversible addition–fragmentation chain transfer (RAFT) agents has always been a challenge for material and polymer scientists. Herein we report 3D printing of RAFT-based formulations that can be conducted fully open to air using a standard digital light processing (DLP) 3D printer and under mild conditions of visible light at blue (λmax = 483 nm, 4.16 mW/cm2) or green (λmax = 532 nm, 0.48 mW/cm2) wavelength. Our approach is based on activation of TTC RAFT agents using eosin Y (EY) as a photoinduced electron-transfer (PET) catalyst in the presence of a reducing agent (triethylamine (TEA)), which facilitated the oxygen tolerant 3D printing process via a reductive PET initiation mechanism. Reactivation of the TTCs present within the polymer networks enables postprinting monomer insertion into the outer layers of an already printed dormant object under a second RAFT process, which provides a pathway to design a more complex 3D printing. To our best knowledge, this is the first example of oxygen tolerant EY/TEA catalyzed PET-RAFT facilitated 3D printing of polymeric materials. We believe that our strategy is a significant step forward in the field of 3D printing.

Progress and Perspectives Beyond Traditional RAFT Polymerization

“…In addition to these applications, oxygen tolerance has also significantly simplified the reaction setup for performing surface-initiated polymerizations, [105,106] and for the translation of RAFT into 3D printing. [107,108] Complimenting the observed improvements in interlayer bonding, the application of RAFT holds the promise of finer control over the nano/microstructure of printed materials and the programming of new functions and stimuli-responsivity.…”

3D printing and growth induced bending based on PET-RAFT polymerization

“…[EY]: [TEA], which was able to be printed under both blue (λmax = 483 nm, 4.16 mW/cm 2 ) and green (λmax = 532 nm, 0.48 mW/cm 2 ) lights 22 . This resin was slower to polymerize compared to conventional free radical polymerization (FRP) equivalents and produced objects with a maximum build speed of 1354 µm/hr under green light.…”

“…Within a network a symmetric RAFT agent will provide intranetwork growth in size and mass by expanding the chains between crosslinking points, whereas an asymmetric RAFT agent will also cause network-wide growth but only at the chain ends, making it more suitable for surface growth and functionalization 20 . Previously our group has demonstrated 3D printing techniques based on photo-RAFT polymerization under various visible wavelengths (405nm, 483nm and 532nm) ; both via an iniferter mechanism under an inert atmosphere 21 , and via PET-RAFT in open air 22 . In both studies we demonstrated the facile surface modification that could be performed on the samples after printing with a range of different monomers; pyrene methyl methacrylate (PyMA) for a light response, N-isopropylacrylamide (NIPAM) for temperature response, and butyl acrylate (BA) to modify the surface hydrophobicity.…”

“…The use of light activation allows such post-production modification to be easily controlled both spatially and temporally under mild conditions, providing a new dimension to 4D "living" polymer materials. Our group has previously worked on RAFT based 3D printing using both iniferter 21 and PET-RAFT 22 processes. Our collaborator the Boyer group have also shown good work with an aqueous based RAFT 3D/4D printing system 15 .…”

“…25 . This tertiary amine pathway is particularly useful, as it is an oxygen tolerant pathway which is highly desirable and necessary for any 3D printing system 15,22 .…”