The new thermal radical initiators (TRIs) based on derivatives of O-imino-isourea have been designed and synthesized. The radical polymerization property of the synthesized TRI derivatives as a radical initiator in n-butyl acrylate was monitored by DSC analysis. TRI derivatives with linear type groups showed peak temperatures (T_peak) of 80-84 ℃, whereas those with cyclic type groups exhibited a wide Tpeak distribution in the 74-87 ℃ range. The polymerization efficiency using new TRIs in n-butyl acrylate was elaborately identified from the molecular weights and conversion rate obtained using GPC analysis and NMR spectroscopy. To consider their possible application to automotive clearcoats, the real-time evolution of the rheological properties of clearcoat resins during the crosslinking process with newly synthesized TRI derivatives was measured, confirming the different crosslinking kinetics of TRI derivatives in real thermal curing process.