DIVALENT COUNTERION BINDING OF NA POLY(ALPHA-HYDROXY ACRYLATE)

Divalent counterion binding has been investigated for Na poly(oc-hydro xy acrylate) (PHANa) in the presence of MgCl2, CaCl2 or BaCl2 by measu ring the reduced viscosity, apparent turbidity and divalent counterion activity of the pertinent aqueous solutions. It was found that the vi scosity decreases in the order, Mg2+ much greater than Ba2+ greater th an or equal to Ca2+, while the turbidity at the devalent counterion ra tio to the polymer, C-2/C-p similar to 0.5, was in the order, Mg2+ > C a2+ greater than or equal to Ba2+ The former order proved to be consis tent with that from the activity measurement. The apparent contradicti on suggested by the result of the turbidity measurement has been inter preted in terms of 'hydration force'. Reference experiments with Na po ly(acrylate) (PAANa) demonstrated that PHANa is able to bind Ca2+ over Mg2+ much more effectively than PAANa, probably through coordination of the alpha-hdyroxyl group to the former counterion. (C) 1997 Elsevie r Science Ltd.