A novel poly(bis(2-methoxyethoxy)phosphazene)graftpoly(ε-caprolactone) copolymer (PMEP-g-PCL) was synthesized and characterized to meet the various demands for biomedical materials.The major advantage of such a copolymer is to reduce the acidity of degradation products

since the basic degradation products of polyphosphazene backbone can neutralize the acidic degradation products of polyester to a certain degree.The copolymer was prepared via ringopening polymerization of ε-caprolactone by using Sn(Ⅱ)2-ethylhexanoate (SnOct2) as catalyst and the hydroxyls in polyphosphazene as initiators.Hydroxy groupfunctionalized polyphosphazenes were obtained in three steps.First

poly［bis(2-methoxyethoxy)phosphazene was synthesized and then its methoxy end groups were partially cleaved by reaction with trimethlsilyl iodide (ISi(CH3)3) to give silylated polymers.At last

the silylated polymers were hydrolyzed to yield polyphosphazenes containing hydroxyl side groups.The amount of hydroxyls along the polyphosphazene backbone could be adjusted by changing the feeding dose of ISi(CH3)3

and polymers with different grafting ratio of —OH had been prepared.However

a significant drawback of this functionalization reaction was that ISi(CH3)3 could induce polymeric backbone cleavage，and molecular weight of polyphosphazene decreased rapidly with increasing the amount of ISi(CH3)3.Besides

the conversion of ISi(CH3)3 was relatively low due to side reactions such as oxidation and hydrolysis.Efforts had been put to improve the reaction via minimizing unwanted reactions.PMEP-g-PCL copolymers with different grafting ratios and lengths of polycaprolactone side chains could be synthesized by using polyphosphazenes bearing various amount of hydroxyls as backbone

as well as by adjusting the feeding dose of ε-caprolactone monomers.The structure of PMEP-g-PCL copolymers was investigated and confirmed by intrinsic viscosity

1H-NMR

FT-IR and DSC analyses.Especially

the DSC measurements demonstrated that the PCL side chains of PMEP-g-PCL possessed lower melting point and crystallinity than the linear PCL with similar molecular weight

for the fact that entanglement is more liable to take place among polymer chains grafted to polyphoaphazene backbone than those in homogeneous PCL homopolymers.And adversely it was strongly suggested that a kind of copolymer with the expected structure

that PCL short chains were attached to polyphosphazene

had been successfully synthesized.These PMEP-g-PCL copolymers could have different degradation behaviors and might serve as potential biomedical materials for the applications in tissue engineering and controlled drug delivery.