Metal-Free Catalyzed Ring-Opening Polymerization of β-Lactones: Synthesis of Amphiphilic Triblock Copolymers Based on Poly(dimethylmalic acid)

Abstract

A polylactide-block-(dimethyl β-malic acid-co-β-butyrolactone)-block-polylactide (PLA-b-P(dMMLA-co-BL)-b-PLA) triblock copolymer has been synthesized according to a totally original three-step strategy. In a first step, the ring-opening polymerization (ROP) of dimethyl benzyl β-malolactonate (dMMLABz) and β-butyrolactone (BL) has been carried out in a toluene/t-BuOH solvent mixture at 80 °C by using ethylene glycol as initiator and the commercially available 1,3,4-triphenyl-4,5-dihydro-1H-1,2,4-triazol-5-ylidene carbene 1 as catalyst. The ROP mechanism selectively involves O-acyl cleavage of both dMMLABz and BL cyclic comonomers with a preferential incorporation of dMMLABz units in the growing polyester chains as attested by 1H NMR spectroscopy. In a second step, the so-produced α,ω-dihydroxy P(dMMLABz-co-BL) copolyester have been further considered as difunctional macroinitiatior in l,l-lactide (LA) monomer ROP at 90 °C. In the third and last step, the benzylic ester functions pending along the recovered...