In the Brookhart type alpha-diirnine palladium catalyst system, it is highly challenging to tune the polymer branching densities through ligand modifications or polymerization conditions. In this contribution, we describe the synthesis and characterization of a series of alpha-diimine ligands and the corresponding palladium catalysts bearing both the dibenzhydryl moiety and with systematically varied ligand sterics. In ethylene polymerization, it is possible to tune the catalytic activities ((0.77-8.85) x 10(5) g/(mol Pd.h)), polymer molecular weights (M-n: (0.2-164.7) x 10(4)), branching densities (25-116/1000C), and polymer melting temperatures (amorphous to 98 degrees C) over a very wide range. In ethylene methyl acrylate (E MA) copolymerization, it is possible to tune the catalytic activities ((0.3-8.8) x 103 g/(mol Pd.h)), copolymer molecular weights (1.1 x 103-79.8 x 103), branching densities (30-119/1000C), and MA incorporation ratio (0.4-13.8%) over a very wide range. The molecular weights and branching densities could also be tuned in alpha-olefin polymerization. The tuning in polymer microstructures leads to significant tuning in polyethylene mechanical properties and the surface properties of the E-MA copolymer.