Abstract: A new block copolymer of ABA type aliphatic polyester, polypiv-alolactone-poly (1 ,2-propandiol adipic acid ester) -polypivalolactone (PPVL-PPA-PPVL) was prepared through the synthesis of dihydroxy terminate PPA, dicarboxyl terminate PPA with succinic anhydride and then tetrabutyl ammonium salt of dicarboxyl terminate PPA by treating with (Bu₄N)₂CO₃-THF and finally by the block copolymerization of tetrabutyl ammonium salt of dicarboxyl terminate PPA with PVL. The conversion of the block copolymerization of PVL was 93-96% and the efficiency of this polymerization was 95-96%,