Heterotelechelic poly(propylene oxide) as migration-inhibited toughening agent in hot lithography based additive manufacturing†
Light-based processing techniques triggering photopolymerization are among the most promising 3D printing technologies due to their benefits regarding resolution, surface quality and build speed. However, the main challenge remains the development of strong and tough materials, since most commercially available photopolymer resins are limited in terms of their thermomechanical performance. We therefore synthesized a heterotelechelic hybrid oligomer based on poly(propylene oxide) (PPO-H), bearing one methacrylic and one addition–fragmentation chain transfer group (AFCT) as end groups. This new compound was successfully implemented as a toughening agent by regulating the network structure via the AFCT mechanism and acted as reactive diluent for highly viscous resins. Formulations containing 10–25 db% (double bond percent) of PPO-H mixed into a commercially available resin (Bomar XR-741MS) were investigated and compared to the corresponding PPO dimethacrylate (PPO-D) mixtures, representing state of the art resins. Full double bond conversion could be reached for PPO-H containing formulations, while shrinkage stress was simultaneously reduced by up to 50% compared to the PPO-D mixtures. Glass transition temperatures decreased with increasing PPO contents. Toughness was enhanced by a factor of 2 (10 db% PPO-H) to 4 (15 db% PPO-H), measured by elongation at break, while decrease in tensile strength remained low (factor of 1.2 and 1.4 for 10 and 15 db% PPO-H, respectively). Impact strength increased by 55 and 92% for 10 and 15 db% PPO-H, respectively. By employing the recently developed Hot Lithography technique, toughened and migration-free 3D printed parts were obtained with PPO-H.