Living Ring-opening Polymerization of O-Carboxyanhydrides Catalyzed by Pyridine Derivatives

Poly(alpha-hydroxy acid)s can be synthesized by ring-opening polymerization(ROP) of O-carboxyanhydrides(OCAs) derived from alpha-hydroxy acids with rich side groups, which make up for the defects of poly(lactic acid) with restricted structure and performance. However, in the process of OCA ring-opening polymerization, chiral alpha-H is prone to racemization, which leads to the decrease of the stereoregularity of the polymer. Here, a high performance organic catalyst with simple structure, 4-methoxypyridine, is capable of rapid catalyzing the living ROP of OCA under the mild conditions, and effectively inhibits the side reactions of transesterification and racemization of chiral alpha-H to synthesize narrowly distributed poly(alpha-hydroxy acid) with high stereoregularity. In addition, although the ROP of OCA in common solvents such as toluene and tetrahydrofuran shows first-order kinetics, that in epoxy solvents follows 0-order kinetics, and the polymerization rate is independent of the monomer concentration. As a novel and efficient Lewis base catalyst, 4-methoxypyridine exhibits a great potential application value in the efficient synthesis of multi-block degradable polyester and preparation of polyester biological pharmaceutical carriers.