Combined Effects of Carbonate and Soft-Segment Molecular Structures on the Nanophase Separation and Properties of Segmented Polyhydroxyurethane

The influence of hard-segment structure on the properties of segmented polyhydroxyurethane (PHU) was investigated using three bis-carbonate molecules: divinylbenzene dicyclocarbonate (DVBDCC), Bisphenol A dicarbonate (BPADC), and resorcinol bis-carbonate (RBC). These carbonates were formulated with poly(tetramethylene oxide) (PTMO)-based and polybutadiene-co-acrylonitrile (PBN)-based soft segments at 40 wt % hard-segment content, resulting in non-isocyanate polyurethanes (NIPUs). Small-angle X-ray scattering, dynamic mechanical analysis, and tensile testing reveal that hard-segment and soft-segment structures may cooperatively influence segmented PHU properties. With PTMO-based soft segment, BPADC yields phase-mixed PHU because of strong intersegmental hydrogen bonding from the hard-segment hydroxyl groups to the soft segment; in contrast, because of moderate intersegmental hydrogen bonding to the PTMO-based soft segment, DVBDCC and RBC lead to nanophase-separated PHUs with 15-17 nm interdomain spacings with substantial, broad interphase regions and low tensile strengths of,similar to 0.40 Is,MPa for DVBDCC and,similar to 0.27 MPa for RBC. By suppressing intersegmental hydrogen bonding via the use of PBN-based soft segment, formulations with all three carbonate molecules lead to nanophase-separated PHUs with interdomain spacings of 1116 nm, narrow interfaces, and improved tensile strengths ranging from 1.6 to 0.5 MPa in the order DVBDCC > BPADC > RBC. All PBN-based PHUs exhibit reversibility of extension with hysteresis similar to that found in thermoplastic polyurethane elastomers.