The viscosity behavior of aqueous poly(viny1 alcohol) (PVA)-borax-NaC1 systems was investigated. The intrinsic viscosity [ q ] of PVA in borax solution increases with increasing borax concentration. In solutions containing both borax and NaCI, on the other hand, [ q ] decreases with increasing concentration of NaCI, and at high NaCl concentration phase separation is observed. In the absence of borax, [ q ] is nearly independent of the NaCl concentration. These results are interpreted in terms of a limited chain expansion due to charges and intrachain crosslinks simultaneously introduced in the PVA chain when the chain is complexed with negatively charged tetrahedral borate ions. The crosslinking density was estimated from the intrinsic viscosity [ q ] , at infinite ionic strength using the Kuhn and Majer equation.
The intrisic viscosity [q] of poly(viny1 alcohol) (PVA) was determined in aqueous solutions with various concentrations q, of borax (N%B40,) as functions of molecular weight Mand concentration cs of NaCl as an added salt. Polyelectrolyte viscosity behaviwr was observed for the systems containing both borax and NaCl, due to the complexation with negatively charged borate ions B(0H)c . [q] changes depending on the ionic strength I. It was found that the Stockmayer-Fixman treatment for the molecular-weight dependence of [q] is valid in the lower molecular-weight range (M < lo5), even though the present PVA chain contains some intrachain crosslinks. Theta conditions can be attained at an appropriate concentration of NaCl. The value of cso is dependent on q,, but the conformational parameter from the Stockmayer-Fixman treatment 4 is almost independent of q,. 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 4' was found to be linearly correlated to a reduced parameter (M/Z)"z for all c, systems, from the slope of which the charge density was estimated.
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