The present invention provides a copolymer which can induce hydrophilic-hydrophobic exchange at a specific temperature and pH, and a liposome complex obtained by compositing with the copolymer, which is capable of releasing inclusion at a specific temperature and pH. The copolymer comprises a repeat unit (a) derived from a monomer represented by the following general formula (1), a repeat unit (b) derived from a carboxyl-group-containing monomer, and a repeat unit(c) derived from a monomer represented by the following general formula (2), and a liposome complex obtained by compositing with the copolymer(In formula (1), R1 represent a hydrogen atom or a methyl group, R2 represents an alkyl group with a carbon number of 1 to 4, n represent a nature number of 1 to 4.)(In formula (2), R3 represent a hydrogen atom or a methyl group, R4 represents an alkyl group with a carbon number of 8 to 20 or an alkenyl group with a carbon number of 8 to 20, m represents a nature number of 1 to 6.)本發明係提供一種在特定的溫度、pH下引起親-疏水變化的共聚物,以及藉由與該共聚物複合化,可在特定溫度、pH下釋放內包物的脂質體複合物。其為具有來自下述通式(1)表示的單體的重複單元(a)、來自含羧基的單體的重複單元(b)、來自下述通式(2)表示的單體的重複單元(c)的共聚物,以及與該共聚物複合化的脂質體複合物。(式(1)中,R1表示氫原子或甲基,R2表示碳原子數為1至4的烷基,n表示1至4的自然數。)(式(2)中,R3表示氫原子或甲基,R4表示碳原子數為8至20的烷基或碳原子數為8至20的烯基,m表示1至6的自然數。)
