Intrinsic viscosity of intramolecularly crosslinked polyelectrolyte: Poly(vinyl alcohol)/borax systems

Abstract

AbstractThe intrisic viscosity [η] of poly(vinyl alcohol) (PVA) was determined in aqueous solutions with various concentrations cb of borax (Na2B4O7) as functions of molecular weight M and concentration cs of NaCl as an added salt. Polyelectrolyte viscosity behaviour was observed for the systems containing both borax and NaCl, due to the complexation with negatively charged borate ions B(OH)−4 · [η] changes depending on the ionic strength I. It was found that the Stock‐mayer‐Fixman treatment for the molecular‐weight dependence of [η] is valid in the lower molecular‐weight range (M < 105), even though the present PVA chain contains some intrachain crosslinks. Theta conditions can be attained at an appropriate concentration cs Θ of NaCl. The value of cs Θ is dependent on cb, but the conformational parameter from the Stockmayer‐Fixman treatment K0 is almost independent of cb. The effect of intrachain crosslinks becomes evident only as a considerably large negative value for the excluded volume parameter B at infinite ionic strength. In addition, the electrostatic part of the expansion factor α was found to be linearly correlated to a reduced parameter (M/I)1/2 for all cb systems, from the slope of which the charge density was estimated.