Interactions between metal chlorides and poly(vinyl pyrrolidone) in concentrated solutionsand solid‐state films

The rheological behavior of poly(vinyl pyrrolidone) (PVP)/N,N-dimethylformamide (DMF) solutions containing metal chlorides (LiCl, CaCl2, and CoCl2) were investigated, and the results showed that the nature of the metal ions and their concentration had an obvious effect on the steady-state rheological behavior of PVP–DMF solutions with different molecular weights. The apparent viscosity of the PVP–DMF solutions increased with an increasing metal-ion concentration, and the viscosity increment was dependent on the metal-ion variety. For a CaCl2-containing PVP–DMF solution, for example, the critical shear rate at the onset of shear thinning became smaller with increasing CaCl2 concentration. It was believed that multiple interactions among metal ions, carbonyl groups of PVP, and amide groups in DMF determined the solution properties of these complex fluids; therefore, 13C NMR spectroscopy was used to detect the interactions in systems of PVP–CaCl2–DMF and PVP–LiCl–DMF solutions. NMR data showed that there were obvious interactions between the metal ions and the carbonyl groups of the PVP segments in the DMF solutions. Furthermore, IR spectra of the PVP/metal chloride composites demonstrated that the interaction between the metal ions and carbonyl groups in the PVP unit occurred and that the PVP chain underwent conformational variations with the metal-ion concentration. DSC results indicated that the glass transition temperatures of the PVP/metal chloride composites increased with the addition of metal ions. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1589–1598, 2007