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Synthesizing different types of sequence-controlled copolyesters can enrich the diversity of copolyesters and modify their properties more precisely, but it is still a challenge to synthesize a complicated sequence-controlled copolyester using different hydroxy acids in a living polymerization manner. In this work, a highly regioselective and stereoselective catalytic system was developed to synthesize biorenewable and biodegradable copolyesters of mandelic acid and lactic acid with isotactic-alternating, heterotactic-alternating, and ABAA-type precise and complicated sequences. Because of the regular incorporation of mandelic acid into polylactide, these sequence-controlled copolymers of mandelic acid and lactic acid show higher glass-transition temperatures than polylactide and a random copolymer. A stereocomplexation interaction between two opposite enantiomeric isotactic polymer chains was also discovered in the isotactic-alternating copolymer.

The ring-opening polymerization (ROP) of O-carboxyanhydrides (OCAs) can give diverse poly(α-hydroxy acid)s (PAHAs) with different functional groups because of easy modification of the side group of OCAs, which can extend applications of PAHAs widely. The stereoselective polymerization of O-carboxyanhydrides and further sequence controlled alternating copolymerization of OCAs were still big challenges until now for lack of suitable catalysts/initiators. In this work, a highly syndioselective ROP of OCAs system as the first stereoselective example in this area is reported using zirconium/hafnium alkoxides as initiators with the highest Pr value up to 0.95. Furthermore, these initiators were successfully applied in the precisely alternating sequence controlled copolymerization of PheOCA and Tyr(Bn)OCA, and alternating copolymerization of LacOCA and PheOCA was also achieved.