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.

Automated summary

The novel organic catalyst 4-methoxypyridine shows high catalytic activity in the living ROP of OCA, enhancing the stereoregularity of the products and preventing side reactions, with great potential applications. Additionally, there are differences in kinetics of ROP under different solvent conditions.