Provided is a block copolymer comprising at least one hydrophilic polymer block (A) and at least one polymer block (B), said polymer block (B) comprising at least one type of repeating unit of the following formula (I)wherein R1 is an aliphatic hydrocarbon group which is optionally substituted with one or more of -OR5, -SR5, -NR6R7, -(NR6R7R8)+, -CONR6R7, -C(O)OR9 and -C(O)R10, wherein R5 to R10 are independently selected from H, aliphatic and aromatic residues, and wherein R1 is selected such that the polymer block (B) is more hydrophobic than the polymer block (A)； and compositions, such as pharmaceutical compositions, formed with the block copolymer.
