Block copolymer of Poly d

L lactide co polyethylene glycol(PLA PEG) was prepared by ring opening polymerization in vacuum at 180℃ with stannous octoate (SnOc2) as catalyst.By composite emulsion technique the PLA PEG microspheres with micron size encapsulating protein were prepared.An apparent reduction of the crystallinity of the microspheres carrying protein compared with that of non carrying protein determined by DSC indicated that protein can be effectively carried in the PLA-PEG microspheres.The size of the microsphaeres was determined by SEM.The quantification of protoin in the microspheres was carried out with BCA reagent. The results showed that comparing with homopolymer PLA

the ether-ester block copolymer PL-A-PEG is more advantageous to microsphere preparation and protein encapsulation.