Polyphosphoesters are a class of biodegradable polymers with repeated phosphoester linkage in the backbone. Due to their biocompatibility and structural similarities to naturally occurring nucleic and teichoic acids, functionalized polyphosphoesters have attracted more and more attention in the last decade and have currently been studied extensively. The phosphorus is a pentavalent atom and can be modified by the incorporation of various substituents, which leads to formation of versatile structures and the easy side-chain functionalization, thus, it allows effective modification of their physical and chemical properties. Therefore polyphosphoesters have been applied in drug/gene delivery, tissue engineering and so on. Among them, the most popular and widely used of such polymers is poly(ethylene phosphate). This review briefly summarizes the structural characteristics of poly(ethylene phosphate) and the controlled synthetic methods, which provide access to novel and complex polymer structures. The article focuses on the various types of synthetic poly(ethylene phosphate) such as linear, star and hyperbranched derivatives, particularly those poly(ethylene phosphate) derivatives that applied in biological fields are highlighted. In addition, on the basis of current research in the fields, this paper presents several representative topologies of poly(ethylene phosphate) and their application in drug/gene deliveries and tissue engineering. At last we propose the prospects of poly(ethylene phosphate) development in life sciences, and we look forward to better communication with other scientists in this field.

Contents
1 Introduction
2 Synthesis of poly(ethylene phosphate)
2.1 Synthesis of poly(ethylene phosphate) monomers
2.2 Ring-open polymerization of poly(ethylene phosphate) monomers
3 Structures of poly(ethylene phosphate)
3.1 Linear poly(ethylene phosphate)
3.2 Star-shape poly(ethylene phosphate)
3.3 Hyperbranched poly(ethylene phosphate)
3.4 Other structures
4 Applications of poly(ethylene phosphate) in biology
4.1 Drug delivery and release
4.2 Gene delivery
4.3 Tissue engineering
5 Conclusions and outlook