A study was carried out in which aqueous solutions of acrylic acid-maleic a
cid copolymer (mole ratio of monomers: 3:2) were diluted with solutions of
various salts [NaCl, MgCl2, CaCl2, SrCl2, ZnCl2, Al(NO3)(3) and Fe(NO3)(3)]
. This copolymer was found to interact with all these salts to make solutio
ns of enhanced acidity that infrared spectroscopy suggested was a result of
charge stabilization of the polyanion by counterions occupying atmospheric
or site-bound locations. The cations of the salts NaCl, MgCl2, CaCl2 and S
rCl2 appeared to occupy atmospheric positions only; in contrast, with poly(
acrylic acid) they showed some site binding. Zinc ions, on the other hand,
gave identical bridging bidentate interactions with both polymers. The cati
ons from the trivalent salts Al(NO3)(3) and Fe(NO3)(3) were atmospheric and
site bound (bridging bidentate), respectively, and these were also differe
nt from their interactions with poly(acrylic acid). The addition of Fe(NO3)
(3) to the copolymer caused gelation, as with poly(acrylic acid), but forma
tion of the gel was slower and did not result in phase separation. (C) 2000
John Wiley & Sons, Inc.