A salt catalyst comprises an ionic complex of i) a nitrogen base comprising one or more guanidine and/or amidine functional groups, and ii) an oxoacid comprising one or more active acid groups, the active acid groups independently comprising a carbonyl group (C═O), sulfoxide group (S═O), and/or a phosphonyl group (P═O) bonded to one or more active hydroxy groups; wherein a ratio of moles of the active hydroxy groups to moles of the guanidine and/or amidine functional groups is greater than 0 and less than 2.0. The salt catalysts are capable of catalyzing ring opening polymerization of cyclic carbonyl compounds.