This chapter describes the use of complexes of the alkaline-earth metals (magnesium, calcium, strontium, and barium) in homogeneous polymerization catalysis. The latest developments in the polymerization of monomers containing C=C unsaturations (ethylene, styrene, dienes, acrylates) and in the ring-opening polymerization (ROP) of cyclic esters [lactides (LA), ε-caprolactone, trimethylene carbonate] are covered. The mechanisms of chain growth polymerization of olefins and immortal ROP of cyclic esters, which is of particular relevance to these metals, are presented. In view of the current interest devoted to the organometallic chemistry of the larger alkaline-earth metals, the implementation of well-defined catalyst systems based on calcium, strontium, and barium for the polymerizations of styrene and lactide is highlighted.
