Biphasic Aromatic Amine-Cured Polybutadiene Polyurethane-Ureas for 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.