Preparation and property controllability of dynamically crosslinked polyurethane modified bitumen

This study presents a dynamically crosslinked synthesis method for polyurethane (PU)-modified bitumen by directly incorporating polyols (PEG-2000), methylene diphenyl diisocyanate (MDI), and additives into asphalt to create an adaptable polymer network. By carefully adjusting the NCO/OH molar ratio between 0.67 and 2.00, targeted control of material properties was achieved. When using excess MDI (NCO/OH > 1.00), the modified asphalt showed improved high-temperature performance with a 12.3 °C rise in softening point, 45 % lower penetration value, and increased viscosity (1.63 Pa·s at 135 °C), consistent with enhanced crosslinking of rigid polymer segments. Conversely, formulations favoring PEG content (NCO/OH < 1.00) demonstrated better flexibility, improving ductility by 4.0 cm through plasticizing effects. The covalent bonds in PU-modified system provided exceptional storage stability, maintaining a 0.6 °C softening point difference compared to 4.5 °C variations observed in conventional SBS-modified asphalt. Comprehensive characterization using FTIR spectroscopy, atomic force microscopy, and thermal analysis confirmed successful PU formation, and identified crosslinking-dependent phase separation. These findings establish a molecular design strategy for engineering asphalt binders with customizable performance profiles to meet diverse pavement requirements.