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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. [ABSTRACT FROM AUTHOR]