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 (λ_max = 483 nm, 4.16 mW/cm²) or green (λ_max = 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.