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 ∼0.40 MPa for DVBDCC and ∼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 11-16 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.