Design and Depolymerization of Bis(2-hydroxyethyl) Terephthalate-Containing Polyurethanes for Vat Photopolymerization

Abstract

Vat photopolymerization (VPP) of highly aromatic polyurethanes (PUs) expands the library of additive manufacturing (AM) materials and enables a vast array of ductile thermoplastics, rigid and flexible thermosets, and elastomers. Aromatic diisocyanates and various diols enable printing of rigid, highly aromatic cross-linked parts, which offer high glass transition temperatures and tunable thermomechanical performance. The judicious control of molecular weight of the photo-reactive telechelic oligomers allows for a fundamental study of the influence of cross-link density in highly aromatic 3D PU printed objects. VPP AM produces objects with high resolution, smooth surface finish, and isotropic mechanical properties. Thermal post-processing is critical in maintaining excellent thermomechanical properties with semi-crystallinity as a function of cross-link density. Due to the presence of two ester carbonyls in the bis(2-hydroxyethyl) terephthalate chain extender, the printed parts are readily amenable to depolymerization with methanolysis to produce difunctional dimethyl dicarbamates under modest reaction conditions. Dimethyl dicarbamates serve as suitable monomers for subsequent polycondensation.