Low-temperature crosslinking characteristics of interpenetrating polymer networks with dual-curable amine-based blocked isocyanate for automotive 1 K clearcoats

Interpenetrating polymer network (IPN) clearcoat systems were developed using two distinct thermal crosslinking reactions: urethane formation reaction and free radical polymerization. Specifically, an amine-based dual-curable blocked isocyanate crosslinker (BI_TBEMA) was employed to establish additional independent networks within IPNs by utilizing dissociated blocking groups through free radical polymerization. To validate the formation of the IPN and its suitability for a low-temperature curing process, the thermal deblocking characteristics and crosslinking dynamics of the dual-curable 1 K clearcoat were confirmed via various experimental methods, including rheological tests, thermogravimetric analyses, dynamic mechanical analyses, and nano-indentation tests. The influence of the IPNs on the crosslinking characteristics was examined and compared with clearcoat systems featuring only a urethane formation network. Both semi-IPN and full-IPN configurations demonstrated enhanced thermal and mechanical properties in contrast to the mono-curable 1 K clearcoat system, especially at low curing temperatures.