Thermal crosslinking characteristics of dual-curable isocyanate blocked with methacrylate-functionalized amine derivatives for eco-friendly automotive clearcoats

A novel isocyanate blocked with an amine derivative blocking agent (2-(tert-butylamino) ethyl methacrylate, TBEMA) was designed as a thermal crosslinker for an eco-friendly automotive clearcoat system. New dual-curable blocked isocyanate (BITBEMA) was effectively deblocked at curing temperatures of 120 and 130 °C, which are lower than the conventional curing temperature of 150 °C. The deblocking features of BITBEMA were verified through experimental measurements and density functional theory simulations. The amine-based blocking agent with the methacrylate functionality directly participated in free radical polymerization with CC double bonds in the main resin (hydroxyl functionalized urethane methacrylate oligomer) during thermal curing, leading to enhanced crosslinking networks as well as reduced emissions of volatile organic compounds. The real-time crosslinking behaviors and mechanical properties of the clearcoat with BITBEMA were compared to those of clearcoats with mono-curable amine-based blocked isocyanate and a commercial crosslinker, confirming the excellent crosslinking characteristics of the dual-curable isocyanate crosslinker.