Radical-initiated copolymerization of N-isopropyl acrylamide (NIPA) with maleic anhydride (MA) and macromolecular reactions of synthesized poly(NIPA-co-MA) with polyethyleneglycol (PEG with a methoxy chain end and molecular weight of 2000 g mol(-1)) and polyethyleneimine (PEI with molecular weight of 2000 g mol(-1)) have been studied as a way to obtain new reactive amphiphilic water-soluble polymers potentially useful as carriers for gene delivery. Structure, composition and thermal behaviour of synthesized copolymers and their macrobranched architectures are determined by MR, H-1 and C-13 NMR spectroscopy, elemental (N content) and chemical (acid number) analysis and differential scanning calorimetry, differential thermal and thermal gravimetric methods. It is shown that synthesized copolymers with given composition have low critical solution temperature (LCST) in the range of 30.2-46.4 degreesC at pH values of 4.0-7.4, which suggest the possibility of their biomedical applications. (C) 2003 Elsevier Science Ltd. All rights reserved.