Copolymerization of polar monomers and olefins catalyzed by transition metal under mild conditions is a challenge. alpha-Diimine palladium complexes have great potential to catalyze the copolymerization of alkylacrylates and olefins. But they are prone to deactivation under mild conditions which limits their industrial application. A novel unsymmetrical alpha-diimine palladium complex with bulkier alpha-diimine ligand was provided in this paper. They were active in ethylene homopolymerization at 80 degrees C. At 50 degrees C they could produce ethylene/methylacrylate copolymer with moderate methylacrylate incorporation. The probable reason for the high thermal stability of these complexes was proposed.