Hybrid aliphatic and aromatic diisocyanates forming mixed urea segments for high-performance polyurea

Abstract

Polyurea is gaining more traction in the realm of protective coatings on metal surfaces from corrosion. The properties of polyurea can be controlled by the judicious selection of its reactants. Herein, a series of polyurea based on hybrid aliphatic/aromatic diisocyanates are synthesized from isophorone diisocyanate (IP) and polycarbodiimide-modified diphenylmethane diisocyanate (ISO). The formulation composed of 37.5:62.5 (IP: ISO) weight ratio yields the highest tensile strength at 47.80 MPa, elongation at 500 %, and hardness of 95 HA. The findings are validated through field emission scanning and atomic force microscopic analysis, which reveals phase mixing surface and ductile fracture containing wide-ranging stretching lines due to enhanced resistance to deformation. Furthermore, synthesized polyureas present a unique stress relaxation pattern with gradual increase in stress under constant deformation, due to hydrogen bond reformation and dislocation creations during chain alignment. IP37.5-ISO62.5 demonstrates outstanding corrosion resistance after a 28-day exposure in salt spray test.