Multifunctional 3D Printing of Heterogeneous Polymer Structures by Laser-Scanning Micro-Stereolithography Using Reversible Addition–Fragmentation Chain-Transfer Polymerization

Stereolithography is the most precise three-dimensional (3D) printing technology and has been applied to various applications with various photocurable materials. However, most 3D-printed objects produced using conventional methods are made of uniform materials, limiting their functions. In this study, to produce heterogeneous 3D-printed objects, microphase-separated structures were controlled by the copolymerization of a photoinduced macro-reversible addition–fragmentation chain-transfer (macro-RAFT) agent and a monomer at different scanning speeds of an ultraviolet laser beam using a laboratory-constructed laser-scanning micro-stereolithography system based on a bottom-up configuration in a fully open-to-air system. First, we demonstrated 3D printing using a RAFT agent by fabricating a pyramidal structure using a 375 nm laser. Copolymerization with styrene was performed to confirm that the synthesized poly(butyl acrylate) with dormant species at the end (DTC-PBA) formed block polymers upon photoirradiation. Nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC) results indicated the formation of a block polymer. A homogeneous photocurable resin was prepared by mixing the synthesized DTC-PBA with multifunctional monomers, and 3D printing was performed using the prepared photocurable resin at different scanning speeds. As the scanning speed increased, the transparency of the 3D-printed model increased, whereas the mechanical strength decreased. It was suggested from scanning probe microscopy (SPM) observations that these differences were due to differences in the microphase-separation structure. As a result, it was demonstrated that heterogeneous 3D structures with sites have different mechanical and optical properties from those of a single material. Controlling the physical properties of 3D-printed parts by controlling the laser irradiation conditions is useful for functionalizing 3D-printed microdevices.