Amines as (co)initiators of cyclic esters' polymerization

A review reports on application of amines as (co)initiators in the ring-opening polymerization of aliphatic cyclic esters. First, the use of tertiary amines (R 3 N) as initiators of the controlled polymerization of highly strained, four-membered β-lactone (P-propiolactone, PL) is described [equation (1)]. Then attempts at the high temperature polymerizations of the medium strained, six- and seven-membered δ- and e-lactones initiated with primary amines (RNH 2 ) or α-amino acids are briefly discussed. Finally, it is shown in more detail that the best results have been obtained recently in the processes catalyzed additionally with tin(II) octoate [Sn(Oct) 2 ]. Mechanisms of these polymerizations are also discussed. Results of the kinetic studies [equation (9) and (10)] as well as 1 H NMR, MALDI TOF mass spectrometry, and size exclusion chromatography (SEC) measurements, carried out in the authors' laboratory, indicate that polymerizations of £-caprolactone (CL) or L,L-lactide (LA) initiated with RNH 2 /Sn(Oct) 2 fulfill living process criteria and therefore allow to fully control the syntheses of the corresponding polymers. The selected syntheses applications, such as preparation of the copolymers N-carboxyan-hydrides of α-aminoacids and LA [equation (7)] or star-shaped polymers based on polyamino dendrimers [formula (I) and (II)] are also described.