the present invention relates to a triblock copolymer used for medical application essentially consisting of : pla , pga , or pla / pga as hydrophobic block , biodegradable peo derivatives synthesized by peos less than 4 , 000 molecular weight by the ester linkage among them as hydrophilic block . the present invention also provides a triblock copolymer easily degradable to the compounds less than m . w . 4 , 000 in order to excrete through the human kidney , which enables its medical application . furthermore , using the triblock copolymer of the present invention , the improved hydrogel materials with broad biochemical applications can be provided due to its biodegradable and thermoplastic properties .