Poly(D,L-lysine)-block-poly(ethylene glycol)-block-poly(D,L-lysine) hydrochloride is a A-B-A type hydrophilic block copolymer that has a poly(D,L-lysine hydrochloride) section on both sides of a non-reactive PEG section. It is a crystalline solid soluble in water. Upon derivatization of the poly(D,L-lysine hydrochloride) parts, it can self-assemble into particles in aqueous solution with a hydrophobic poly(D,L-lysine) core and a hydrophilic PEG shell.