Synthesis Of PEG-PCL Block Copolymers And Preparation Of Microspheres

Biodegradable polymer materials because of their good biodegradability and biocompatibility have been used to great applications in the domain of biomedicine.In order to improve the hydrophilic property of aliphatic polyesters,such as poly(ε-caprolactone)(PCL), the p01y(ethylene oxide)(PEO) blocks were introduced into the polyester by using copolymerization.Amphiphilic diblock copolymer of PCL-PEG has been synthesized. Polymer microspheres have been prepared and their enzymatic degradation behavior have been investigated.In this work,a series of amino-terminated PEG homopolymer with different molecular weight 2000,3000,4000 were synthesized by anionic polymerization in the presence of the initiator Potassium bis(trimethylsilyl) amide ([(CH₃)₃Si]₂NK). According to the method based on amidation reaction, amino-terminated PEG were successfully converted to carboxyl-terminated and hydroxyl-terminated PEG.The molecular weight of the polymer can be accurately controlled by the molar ratio of monomer to initator. GPC and NMR data supported the structure of the polymer.It showed that the molecular weight of the polymer were accorded with the designed data, and molecular weight distribution was between 1.04 and 1.15.Amino-terminated PEG_m-PCL_n(the subscript "m" and "n" denote the designed molecular weight of PEG and PCL blocks,respectively.m=1k, n=4k,10k,20k)were synthesized by sequential addition of two monomers(EO and CL) in the presence of the initiator Potassium bis(trimethylsilyl) amide ([(CH₃)₃Si]₂NK).The method was compared with the traditional method using stannous octoate (Sn(Oct)₂) as the catalyst of the synthesis of PEG-PCL.Carboxyl-terminated PEG-PCL were achieved by amidation reaction of amino-terminated PEG-PCL.The polymeric structure has been conformed by many kinds of analytical methods.The molecular weight of the synthesized copolymers were in the range of 10000 to 20000 and the molecular weight distribution was between 1.20 and 1.35.PCL homopolymer and the three kinds of PEG-PCL block copolymers with monomethoxy, amino and carboxyl group ended in the PEG segment respectively were used to prepare microspheres by water-in-oil-in-water (W/O/W) double emulsion solvent extraction/evaporation technique. Enzymatic degradation of the microspheres was performed in a pH 7.0 phosphate buffer solution containing enzyme. GPC and SEM were used to study the degradation behavior of the polymer microspheres.