PEI-b(20k)-mPEG(1k) comprises polyethylene glycol (PEG) and poly(ethylene imine) (PEI) witha terminal hydroxyl group. The hydrophilic PEG increases solubility in aqueous media. PEI has temperature dependent solubility in aqueous media and finds many applications in industry. PEI-b-mPEG can be used in the development of lipid nanoparticles. The terminal hydroxyl group enables further derivatization or replacement with other reactive functional groups.