Semicrystalline Non-Isocyanate Polyhydroxyurethanes as Thermoplastics and Thermoplastic Elastomers and Their Use in 3D Printing by Fused Filament Fabrication

Chemical fixation of the greenhouse gas carbon dioxide with diepoxides followed by melt-phase polyaddition of the resulting difunctional cyclic carbonates with 1,12-diaminododecane (DDA) yields semicrystalline polyhydroxurethane (PHU) thermoplastics. Also, 100% biobased semicrystalline PHU thermoplastics are feasible. Opposite to conventional polyurethane syntheses, neither isocyanates nor phosgene are required as intermediates. Preferably, melt-phase polyaddition is performed in a twin-screw compounder in the absence of catalysts, which also catalyze side-reactions. Calorimetric measurements and small-angle X-ray scattering reveal the fundamental structure–property relationships governing PHU crystallization. The PHU melting temperatures vary between 40 and 115 °C, and PHU Young’s moduli range from 220 to 1430 MPa. Moreover, non-isocyanate PHU thermoplastic elastomers (TPHE) are readily tailored via melt-phase polyaddition of diamine-terminated flexible PHU prepolymers serving as soft segments combined with semicrystalline PHU as hard segments. As verified by means of thermal analysis (DSC), dynamic mechanical analysis (DMA), X-ray diffraction (SAXS), and microscopy (AFM), the careful balance between soft and semicrystalline hard-segment incorporation accounts for nanophase-separation, which in the past has failed as a result of phase intermixing resulting from strong hydrogen bonding between soft and hard segments. For the first time, tailored PHU thermoplastics are employed in extrusion-based additive manufacturing by means of fused deposition modeling (FDM) or fused filament fabrication (FFF). Clearly, the presence of hydroxyl groups and their hydrogen bonding improves filament fusion and adhesion essential for achieving mechanical properties similar to PHU melt extrusion without encountering warpage.