Aliphatic polyesters are a class of biodegradable, biocompatible, and environmentally friendly polymers, which have been widely used in many fields, such as packaging, agricultural film, biomedical materials, etc. In comparison with the polycondensation reaction, the ring-opening polymerization (ROP) of lactones could be conducted in mild conditions with no small-molecular byproducts formed in the polymerization process. In addition, ROP of lactones is suitable to synthesize the aliphatic polyesters with high molecular weight and narrow molecular weight distribution. At present, the aliphatic polyesters are usually synthesized by the coordination polymerization with the metal complexes as catalysts. The as-prepared polymers inevitably contain a small amount of metal ions that are difficult to be removed completely, which limits the applications of aliphatic polyesters in the biomedical fields. Due to the low cost, ease of preparation, and low toxicity of non-metallic organocatalysts, the ROP of lactones catalyzed by non-metallic organocatalysts has drawn much attention in recent years. According to the catalytic mechanisms, this paper will focus on the non-metallic organocatalysts with the hydrogen-bonding interactions and review the recent research progress on the hydrogen bonding-based non-metallic organocatalysts used for ROP of lactones.
Contents
1 Introduction
2 Monofunctional hydrogen-bonding catalysts
2.1 DBU
2.2 MTBD
2.3 Phosphazenes
3 Bifunctional hydrogen-bonding catalysts
3.1 4-Dimethylaminopyridine
3.2 Thiourea-amine catalyst
3.3 1,5,7-Triazabicyclo[4.4.0] dec-5-ene
3.4 Other bifunctional catalysts
4 Combined catalyst systems
4.1 Combined neutral catalyst systems
4.2 Combined ionic catalyst systems
5 Conclusion