Web Release Date: August 15,
Temperature-Induced Collapse of Alkaline Earth Cation-Polyacrylate Anion Complexes
and
Chemistry Department, Universität Paderborn, Warburger Strasse 100, D-33089 Paderborn, Germany, and Institute Laue-Langevin, LSS Group, B. P. 156, 6, rue Jules Horowitz, F-38042 Grenoble, Cedex 9, France
Received: December 1, 2006
In Final Form: June 29, 2007
Abstract:
Polyacrylate anions are used to inhibit CaCO3 precipitation and may be a promising additive to control formation
of inorganic nanoparticles. The origin of this applicability lies in specific interactions between the alkaline
earth cations and the carboxylate functions along the polyacrylate chains. In the absence of CO32- anions,
these interactions eventually cause precipitation of polyelectrolytes. Extended investigation of dilute sodium
polyacrylate solutions approaching this precipitation threshold revealed a dramatic shrinking of the PA coil
dimensions once the threshold is reached (Eur. Phys. J. E 2001, 5, 117). Recent isothermal calorimetric
titration experiments by Antonietti et al. (Macromolecules 2004, 37, 3444) indicated that the driving force of
this precipitation is entropic in nature. In the present work, we investigated the impact of temperature on the
structural changes of dissolved polyacrylate chains decorated with alkaline earth cations. To this end, large
polyacrylate chains were brought close to the precipitation threshold by the addition of distinct amounts of
Ca2+ or Sr2+ cations. The resulting structural intermediates were then subjected to temperature variations in
the range of 15 
C 
T 40 C, and the accompanying structural changes of the polyacrylate coils were
recorded by means of light and neutron scattering. As a major result, we could unambiguously demonstrate
that the coils can reversibly be collapsed and extended by increasing and decreasing the temperature,
respectively.
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