The invention provides a block copolypeptide comprising a hydrophilic heteropolypeptide block (A) and a hydrophobic homopolypeptide block (B). There is also provided a polymersome comprising a block copolypeptide of the invention. The invention further provides a method for preparing a copolymer comprising ring-opening polymerisation (ROP) of an amino acid N-carboxyanhydride (NCA) initiated from a peptide.
