Controlling mechanical properties of 3D printed polymer composites through photoinduced reversible addition-fragmentation chain transfer (RAFT) polymerization

Reversible addition-fragmentation chain-transfer (RAFT) polymerization has been widely exploited to produce homogeneous and living polymer networks for advanced material design. In this work, we incorporate silica nanoparticles (SNPs) into a RAFT polymerization system to prepare a series of photocurable composite resins. These resins are applied to stereolithographic 3D printing to produce composite materials with enhanced mechanical properties. Relatively high loadings of SNPs (30 wt%) within the resins are achieved, allowing an increase in the 3D printed composite material tensile strength by 165% while simultaneously increasing the fracture toughness by 168%, compared with the pristine polymer materials. In addition, the inclusion of small amounts (1 wt%) of RAFT agent into the 3D printing resins also provide efficient control over thermomechanical, tensile, and fracture properties of the resulting materials. In particular, 3D printed SNP composite materials containing 30 wt% SNPs and 1 wt% RAFT show a 37% increase in elongation at break values and a 60% increase in tensile strength compared with free radical polymerization-based counterparts. The increased ductility of composite materials imparted via RAFT agent addition has not been reported and could provide a useful tool for optimizing the performance of composite materials prepared by 3D printing. Additionally, photoinduced reactivation of thiocarbonylthio groups provides access to spatially controlled post-printing functionalization of the surface of the composite materials. As such, RAFT-mediated 3D printing of composite resins is shown to be an effective strategy for developing composite materials with arbitrary combinations of well-defined mechanical properties and diverse chemical functionalities for material post-modification.