Methoxy-poly(ethylene glycol)-block-poly(L-lysine trifluoroacetate) is a linear hydrophilic block copolymer which has a poly(L-lysine trifluoroacetate) section and a non-reactive PEG section. It is a solid soluble in water and polar organic solvents such as DMF. Upon derivatization of the poly(L-lysine trifluoroacetate) part, it can self-assemble into particles in aqueous solution with a hydrophobic poly(L-lysine) core and a hydrophilic PEG shell.