molecular weight 550 dissolved in 200 ml of dmf immediately followed by the addition of 29 g 0 173 mole of hdi the temperature was set at 50 u00b0 c and the reaction was performed in a nitrogen atmosphere after 5 hours of reaction 172 9 g 0 0865 mole of pcl diol molecular weight 2000 was added the temperature was raised to 100 u00b0 c and the reaction was continued overnight then the reaction was quenched by dba after the resultant was cooled down it was precipitated by 1000 ml of ether and the resulting precipitates were dissolved in dmf and precipitated from ether such precipitation process was repeated three times then the precipitates were vacuumed until dry yielding a peg530 pcl2000 peg530 tri block copolymer the cmc of the product was about 0 013 wt determined by the method as described in example 1 the size of the resulting micelles was determined using a dynamic light scattering instrument malvern uk 44 of malvern instruments company to be about 85 nm as shown in fig3 suitable amount of dbtdl was added to 100 g 0 05 mole of methoxy polyethylene glycol molecular weight 2000 dissolved in 200 ml of dmf immediately followed by the addition of 7 98 g 0 0475 mole of hdi the temperature was set at 50 u00b0 c and the reaction was performed in a nitrogen atmosphere after 5 hours of reaction 47 5 g 0 02375 mole of pcl diol molecular weight 2000 was added the temperature was raised to 100 u00b0 c and the reaction was continued overnight then the reaction was quenched by dba after the resultant was cooled down it was precipitated by 1000 ml of ether and the resulting precipitates were dissolved in dmf and precipitated from ether.