Nanoparticulate polyelectrolyte complexes of thermally sensitive poly(l-lysine)-based copolymers and DNA

•Hybrid copolymers of the type (PNIPAm)77-g-(PEG)9-b-poly(l-lysine)z were synthesized.•Micelle-like nanosized particles were obtained by abrupt heating of their dilute aqueous solutions.•The micelle-like structures exhibited strong ability to condense DNA.•Well-defined, colloidally stable, and non-toxic polyplex particles were formed.•The hybrid copolymers are promising gene-delivery vector materials.