Controlled Micro- and Nanostructure in Light Driven 3D Printing

Stereolithography (SL) is highly effective for small-volume manufacturing and rapid prototyping because of its ability to create objects relatively quickly with intricate features at resolutions down to 150 µm. Widespread adoption of SL for structural applications faces several obstacles including unsuitable thermomechanical performance and anisotropic properties from network inhomogeneities. In this work, we attempt to overcome such challenges by controlling the nano/microstructure of cross-linked polymer networks in printed objects. We have found that incorporating a small amount of reversible addition-fragmentation chain-transfer (RAFT) agent into acrylate printing formulations mediated the cross-linking reaction and led to delayed vitrification and reduced internal stress. These changes resulted in 45% increase in elongation and toughness compared to non-RAFT controls with significant decreases in anisotropic properties. Additionally, we synthesized custom block copolymers to control cross-link density without sacrificing strength. Copolymers with strategically placed hydroxyl pendant groups enabled reduced internal stress while improving structural integrity through physical hydrogen bonding. Incorporation of copolymers into a 3D printing model acrylate formulation led to objects with more than 500% increase in impact strength. Most recently, we combined orthogonal radical and cationic polymerizations into hybrid printing resins that can sustain fast build speeds and provide improved mechanical properties. During photopolymerization, these hybrid systems phase separate, and the extent of nanoscale phase separation/polymer morphology was chemically controlled through small modifications in cationic comonomer composition. Smaller phase separation size scales exhibited the greatest impact strength due to reduced dispersity of contrasting morphology increasing interlayer adhesion. Ultimately, hybrid polymer morphologies with controlled phase separation provide exceptional augmentation in mechanical performance with hybrid polymers exhibiting a 900% increase in material toughness relative to component materials.