alpha-Diimine complexes of palladium and nickel catalyze the polymerization of alpha-olefins to give new materials that range from low-T-g elastomers to low-melting, partially crystalline polymers. The H-1 and C-13 NMR spectra of the resulting polymers have been assigned in detail. Many unique microstructural features of the complex polymers have been identified. Mechanistic models that involve the 1,2- and 2,1-insertion of the alpha-olefins, chain walking, and insertion at certain points along the chain have been constructed. The complex microstructures can be explained using a small set of rules for palladium catalysts which is expanded slightly to account for the nickel catalysts.