Vinylpyrrolidone–N,N′-dimethylacrylamide water-soluble copolymers: synthesis, physical–chemical properties and proteic interactions

The radical copolymerization of N-vinyl-2-pyrrolidone (NVP) with N,N′-dimethylacrylamide (DMAm) has been studied. The copolymer compositions were determined from 1H-NMR. The radical reactivity ratios for DMAm (M1) and VP (M2) were found to be r1=2.232 and r2=0.186. An analysis of the water vapor absorption isotherms as a function of the lactam content in the copolymer is reported. It was observed that the water vapor absorption decreases with increasing VP content in the copolymer and show anomalous diffusion behavior with increasing temperature due to the coupling of diffusion and polymer relaxation mechanisms. From the water vapor sorption data the Arrhenius activation parameter (ED) and enthalpy of sorption (ΔHs) were determined. The activation parameters are found to follow the conventional trend. The poly(DMAm-co-VP) copolymers exhibited a decreased critical solution temperature (LCST) in proportion to their lactam content. Contact angle data were evaluated for the determination of surface free energy components (γdSV, γpSV and γSV) of the synthesized polymers. The dispersion force component (γdSV) of copolymers increased only slightly with the VP content whereas the polar force component (γpSV) decreased with the lactam content. No dependence was observed between the surface free energy (γSV) and copolymer compositions. The complex formation between bovine serum albumin (BSA) and the VP–DMAm copolymers in water was studied by fluorescence spectroscopy. It was found that the copolymers bind to BSA non-specifically on the surface. Phase separation was not observed after addition of copolymers to BSA solutions at pH higher or lower than isoelectric point of BSA.