Waterborne Polyurethane Latexes for Vat Photopolymerization
Ren H. Bean, Garvit Nayyar, Jose I. Sintas, Timothy E. Long
Abstract
Vat photopolymerization (VP) additive manufacturing (AM) provides printed objects with micrometer-scale resolution and a smooth surface finish from a wide range of photo-cross-linkable polymeric precursors. However, viscosity limitations constrain VP to oligomers and monomers with viscosities below 10 Pa·s. This constraint presents a challenging paradox to leverage the advantageous properties of entangled high-molecular-weight polymers while maintaining viscosities suitable for VP processes. This work describes synthetic strategies for developing waterborne polyurethanes (WPUs) for implementation with commercially available VP additive manufacturing platforms. Aqueous latexes of high- and low-molecular-weight polyurethanes effectively decouple the molecular weight–viscosity relationship through sequestering of the polymer to a discrete nanoscale phase. The aqueous phase together with water-soluble reactive diluents provides a photocurable, low viscosity VP composition. Subsequent thermal postprocessing removes water and promotes coalescence of dispersed nanoparticles within the scaffold, forming a semi-interpenetrating network (sIPN) or interpenetrating network (IPN) depending on WPU end-group functionality. This work describes printing low-molecular-weight WPUs with excellent resolution compared to high-molecular-weight WPUs that enable tensile elongations approaching 300%.