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

Abstract

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 (BITBEMA) 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.