A small molecule core (TMP-SK3)with three terminal carboxyl groups was synthesized successfully by the reaction of 1

1

1-trihydroxymethylpropane with the excessive sebacic acid diacetic anhydride.Then

the core molecule was used as a coupling agent to condensate with polyethylene glycols (PEG)of different molecular weight or polyethylene glycol monomethyl ether (PEGm)in the presence of stannous octoate as catalyst and diphenyl ether as azeotropic agent to remove water.Thus

the three-arm star-shaped polyethylene glycol was obtained successfully

and was characterized by 1H-NMR

DSC

GPC and XRD

etc.DSC measurements indicate that the crystallizing temperature and the melting temperature of the three-arm star-shaped polyethylene glycol were different from those of the corresponding linear PEG because the existing of TMP-SK3 altered its crystallizing velocity and the perfect degree of crystals.