Synthesis of polymers of defined stereochemistry has been actively pursued in both industrial and academic laboratories. In 1949, Baggett and Pruitt of Dow Chemical discovered that iron(III) chloride reacted with propylene oxide to form poly(propylene oxide), which could be divided into amorphous and semicrystalline materials using solvent fractionation. The polymer is regioregular when only one process dominates; it is regioirregular when both processes occur. In regioregular poly(propylene oxide), every repeat unit is oriented the same way, giving exclusive head-to-tail (HT) linkages. Assuming the production of regioregular polyether, stereocontrol in epoxide polymerization can take place in two ways. In a chain-growth polymerization reaction, the end of the polymer chain remains at the active metal center during monomer enchainment. it is hoped that further catalyst development will lead to polymers with attractive properties and applications.