LAUSR

Abstract A series of phosphoric acid derivatives have been synthesised and their catalytic activity in the ring opening polymerisation of β-Butyrolactone (β-BL), ɛ-caprolactone and rac -lactide probed. Improved synthetic protocols and characterisation data are provided for a range of catalysts substituted with functional groups altering their electron density and p K a . Lower rates are observed for β-BL polymerisations than other aliphatic cyclic esters. By exploring the reaction kinetics and in situ NMR spectroscopy, we show that the activity decreases due to competitive formation of an off-cycle deactivated species through cleavage of catalyst P O bonds.