Biphasic AromaticAmine-Cured Polybutadiene Polyurethane-Ureasfor Simultaneous Bonding of Materials with Different Polarities

In this study, aromatic amine curing agents (A-HD, A-NPG, and A-DCP) were synthesized through the Michael addition of 3-aminobenzylamine with 1,6-hexanediol diacrylate, neopentyl glycol diacrylate, and octahydro-1H-4,7-methanoindene-1,5-diyldimethanediyl bisprop-2-enoate, respectively. The incorporation of these aromatic amine curing agents into low-polarity polybutadiene polyurethane-ureas balanced the polar and dispersion components of surface energy, enhancing the simultaneous bonding performance with materials of different polarities. Atomic force microscopy revealed that the prepared polybutadiene polyurethane-ureas exhibited a significant microphase separation between the soft and hard segments. The polybutadiene soft segments facilitated bonding to low-polarity materials, while the isocyanate and aromatic amine hard segments enabled effective adhesion to polar materials. Moreover, the viscosity and pot life of the polyurethane–urea mixture can be controlled through the modulation of intermediate structures of aromatic amine curing agents. The polyurethane–urea sample PU-DCP achieved the highest shear bonding strength of 4.36 MPa between steel sheets (a polar material) and styrene–butadiene rubber (a low-polarity material). This strength was 39% and 53% higher than those of polybutadiene polyurethane-ureas cured with the commonly used curing agents 4,4′-methylene bis(2-chloroaniline) (MOCA) and dimethyl thio-toluene diamine (E300). This paper presents a method to achieve effective bonding between low-polarity and polar materials through the modulation of the phase-separated structure in polyurethanes.