Polyurethane coatings from formulations with low isocyanate content using a transurethane polycondensation route

Abstract

A strategy aiming to decrease the amount of isocyanate in the PU industries without changing their current facilities is proposed. Hydroxyl terminated non-isocyanate polyurethane (NIPU) oligomers (H-Ol) with controlled molecular weights and chemical structures have been prepared as precursors. They were prepared by transurethane polycondensation between bis(methylcarbamate) (BMC), hydroxyterminated poly(tetramethyleneoxide) (PTMO) and butanediol at several molar ratios. H-Ol were then reacted with a polyisocyanurate as crosslinking agent to afford several partially NIPU coatings. Polyurethanes based on the PTMO polyols and the polyisocyanurate were also prepared as controls to highlight the importance of the urethane function in the H-Ol. The influence of the chemical structures on the thermal and mechanical properties of the final coatings has been investigated. The prepared coatings displayed thermal stabilities above 200 °C, Young modulus ranging from 3 to 64 MPa, tensile strength values from 0.9 to 17 MPa and elongation at break varying from 25 to 530%. H-Ol with the highest urethane content gave a coating with the best adhesion properties on a metal surface. All the obtained properties were within the characteristic range of two commercial PU reference coatings.