Transition metal alkyls and hydrides isolated from Ziegler-type catalyst mixtures serve as appropriate models for coordination polymerization. These transition metal complexes initiate the polymerization of some vinyl compounds and aldehydes. In some cases the monomer-coordinated complexes may be isolated and the interaction of the monomer with the transition metal complexes may be studied. Comparison of the polymerization kinetics of the vinyl compounds with the decay kinetics of the initial transition metal complexes on interaction with the monomer provided important information with respect to the mechanism of coordination polymerization by these complexes. The effect of organoaluminum compounds on the reactivity of the transition metal complexes has been also studied. These transition metal alkyls initiate the polymerization of acetaldehyde to give a polyether-type polymer at -78°C and a polymer with OH groups at room temperature.