Tuning the properties of segmented polyhydroxyurethanes via chain extender structure

The influence of chain extender structure on the properties of segmented polyhydroxyurethane (PHU) was investigated with four diamine molecules: 1,4-diaminobutane, isophorone diamine, methylene bis(cyclohexyl amine), and bis(aminomethyl) norbornane. These nonisocyanate polyurethanes were synthesized with polytetramethylene oxide-based soft segment and divinyl benzene dicyclocarbonate (DVBDCC) as hard segment. They were characterized with small-angle X-ray scattering (SAXS), dynamic mechanical analysis (DMA), and tensile testing. All PHUs possess nanophase-separated morphology with interdomain spacings of 12 to 16 nm via SAXS. DMA shows that the nanophase separation is accompanied with broad interphases having a wide range of local compositions. These PHUs exhibit tan δ ≥ 0.30 over broad temperature ranges, indicating their potential as effective damping materials. The flow temperature (T_flow), the temperature range with tan δ ≥ 0.30, and the tensile properties of these PHUs are strongly affected by the molecular structure of the chain extender used in synthesis. At 50 wt % hard-segment content, values of T_flow, tensile strength, and elongation-at-break can be tuned via chain extender from 57 to 105 °C, 1.6 to 22.4 MPa, and 70 to 500%, respectively. Notably, PHU at 50 wt % hard-segment content, synthesized with norbornane-based chain extender exhibits the best thermal and mechanical properties with T_flow of 105 °C, tensile strength of 22.4 MPa, elongation-at-break of 500%, and tan δ ≥ 0.30 over 74 °C in breadth. By varying hard-segment content between 30 and 50 wt %, norbornane-based PHUs afford broad tunability in tensile strength from 0.5 to 22.4 MPa with tan δ ≥ 0.30 spanning temperature range as large as 85 °C.