Abstract: A branched hetero polyfunctional polyoxyalkylene compound represented by the following formula (1): wherein Z represents a hydroxyl group-removed residue of pentaerythritol or dipentaerythritol, OA1 and OA2 represent an oxyalkylene group having 2 to 4 carbon atoms, L1, L2 and L3 represent an alkylene group or an alkylene group that contains an ester bond, a urethane bond, an amide bond, an ether bond, a carbonate bond, a secondary amino group or a urea bond, X and Y are different from each other and represent a functional group capable of a chemical reaction; m and n are an average number of moles of the oxyalkylene group added, m represents 5 to 1,000, n represents 0 to 1,000, and p, q and r represent 0 or 1; and s1 is an integer of 2 or more and s1+s2=4 or 6.

Abstract: Provided is a polyethylene glycol derivative which contains two PEG chains, which is bound to a diacylglycerol, which has high purity, and which enhances the stability of liposomes. Polyethylene glycol is represented by the following formula (1) and which is bound to a diacylglycerol: In Formula (1), R1 is a hydrocarbon group containing 1 to 7 carbon atoms, R2 is an alkyl or alkenyl group containing 9 to 21 carbon atoms, n is the average number of moles of added polyethylene glycol chains, 10 n 100, and X is a linker site between branched polyethylene glycol and the diacylglycerol and is represented by the following formula (2): In Formula (2), Y is an ether bond, an ester bond, a urethane bond, an amide bond, or a carbonate bond and 1 and m are an integer of 0 to 6.