Polymerization of lactide initiated by primary amines and catalyzed by a protic acid

• Polymerization rate of lactide initiated by primary amines increases upon acid addition.
• Polymerization proceeds by cationic activated monomer mechanism.
• Amine (amino acid) end group is bound to PLA chain by stable amide linkage.
• Obtained products are free from metal contaminants.

The polymerization of lactide performed in the presence of primary amines and a protic acid was reinvestigated. The polymerization products obtained at different [protic acid]/[amine] ratios were analyzed by 1H NMR, GPC and MALDI TOF assays. Kinetic experiments proved that the addition of the acid resulted in an increase in the polymerization rate. It was shown that the amine is an efficient initiator in this process and that the protic acid is a cationic catalyst. The possibility of using different amino acids as the initiators of the acid-catalyzed lactide polymerization was also indicated.

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