AABB-Type Copolyester Synthesis via Highly Alternating Ring-Opening Copolymerization of Lactide and Benzylglycolide and Detailed Alternating Level Analyses

Synthesizing different sequence-type bio-polyesters is a valuable and challenging task via a living polymerization method. In this work, a highly heteroselective ring-opening polymerization of rac-benzylglycolide was reported with a high P-r value of 0.94. Then, a stereospecific method was utilized to synthesize the first AABB-type sequence-controlled bio-polyester of lactic acid and benzyl glycolic acid via the alternating polymerization of L-lactide (L-LA) and D-benzylglycolide (D-BG) with a high alternating level of 94%. Importantly, it is pointed out in this work that the alternating level of copolymer is an average value of two alternating probabilities after two different monomer units of lactic acid and benzyl glycolic acid in the polymer chain, respectively. The alternating probability after different monomer units can be calculated using C-13 NMR and H-1 NMR spectra, which also can be verified by a chain end ratio analysis method. The high alternating level of copolymer of L-LA and D-BG can be further confirmed via the analysis of its MALDI-TOF-mass spectrum.