Dual-curable coatings obtained from multi-functional non-isocyanate polyurethane oligomers

Abstract

The growing concerns and impending regulations on the usage of monomeric isocyanates in the production of polyurethane resins have led to the introduction of alternative non-isocyanate polyurethane (NIPU) systems. Although two-component NIPU coatings based on the reaction of cyclic carbonates and aliphatic amines have emerged as a promising option, they are still associated with two significant drawbacks: lower crosslinking densities due to reduced functionality of the oligomers and low ambient-temperature reactivity. This study reports the utilization of a hybrid approach to address these drawbacks. Amine-functional NIPU oligomers (NI-PUPA) were synthesized by the reaction of cycloaliphatic amine functional compounds and multi-functional cyclic carbonates in an excess amine molar ratio. After mixing the NI-PUPAs with (3-glycidyloxypropyl) trimethoxysilane (GPTMS), a dual-curable coating could be achieved by ambient curing of amines and epoxies and moisture curing of alkoxy silanes. A comparative experimental design was implemented to evaluate the effect of an additional curing mechanism. The results revealed that the additional moisture curing led to faster ambient curing, faster development of properties, enhanced flexibility even at higher crosslinking densities, and better corrosion resistance. Such advancement could facilitate the future implementation of NIPUs in high-performance ambient-curing coating applications.