It was not until 1987 when two chemists, Hedrick and Schlemper, from the University of Freiburg proposed the use of phosphazene bases to speed up the reaction and lower the polydispersity index. Up until 2023, three different phosphazene bases have been used in PPA polymerization. Moreover, most of the published research articles describing PPA synthesis between 2008 and 2023 revolve around the usage of LAP, rendering it the most common and effective polymerization technique.