Bioengineering functional copolymers. IX. synthesis and characterization of stimuli-responsive Poly(N-isopropylacrylamide-co-N-vinyl-2-pyrrolidone) and Its Cu(II) complexes

Radical copolymerization of N-isopropylacrylamide (NIPA) with N-vinyl-2-pyrrolidone (VP) were carried out with 2,2'- azobisisobutyronitrile (AIBN) as an intiator in N,N'-dimethylformamide solution at $65^ oC$ under nitrogen atmosphere. Cu(II)-copolymer macrocomplexes were prepared by incorporation of copolymers with copper sulfate in aqueous solution at $40^ oC$. Structure and composition of the obtained copolymers, and the formation of coordinated Cu(II)- complexes between amide VP unit and Cu(II) ions were studied by FTIR spectroscopy, DSC and TGA-DTG methods, as well as by the electrical conductivity measurements. Compositon of the copolymers synthesized in a wide range of monomer feed ratios were determined by FTIR and $^ 1H (^ {13}C)$ NMR-DEPT-135 spectroscopy. The monomer reactivity ratios were determined by Fineman-Ross, Kelen-Tüdös and non-linear regression methods. It was observed that studied monomer pair has some tendency to alternation in the chosen monomer feed ratios due to formation of intermolecular interaction through H-bonding and N→O=C coordination. The copolymers predominantly show amorphous structure while their Cu(II)-macrocomplexes exhibit crystalline phase. The conductive properties of the synthesized Cu(II)-poly(VP-co-NIPA) complexes was also discussed.The synthesized poly(NIPA-co-VP)s show temperature sensitiveness ($T _s$) and higher glass-transition temperature ($T _g$) and thermal stability, polyelectrolyte and stimuli-responsive (temperature- and pH-sensitive) behavior, and can be attributed to the class of bioengineering functional copolymers useful for application in various gene- and bioengineering processes, drug delivery systems, and biomacromolecule conjugations.