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

The intrisic viscosity η] of poly(vinyl alcohol) (PVA) was determined in aqueous solutions with various concentrations c_b of borax (Na₂B₄O₇) as functions of molecular weight M and concentration c_s 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 c_{s Θ} of NaCl. The value of c_{s Θ} is dependent on c_b, but the conformational parameter from the Stockmayer-Fixman treatment K₀ is almost independent of c_b. 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 c_b systems, from the slope of which the charge density was estimated.