Macrogelation of poly(acrylic acid) dispersions through crosslinking

The reaction of poly(acrylic acid) dispersions with diglycidyl ether or dicarboxylic dichlorides as crosslinking agents leads to the formation of macrogels without shrinking of the original dispersions. The particles of the dispersion are stabilized by block copolymers and are about 100 nm in diameter. Micrographs of scanning electron microscopy of the freeze-dried gel show a three-dimensional network structure formed by the particles. The kinetics of the crosslinking reaction was studied by differential scanning calorimetry. A model is presented considering a partition equilibrium of the crosslinking agent between the disperse and the continuous phase and the influence of mass transport of the crosslinking molecules in the interior of the particle. By means of dynamic rheology it was shown that the macrogels obtained are the result of chemical crosslinking reactions between the particles. Frequency-dependent measurements of the dynamic modulus during the crosslinking reaction showed that the network formation is a reaction-controlled cluster-cluster aggregation process. Dynamic light scattering experiments indicate a dominating cluster fraction with sizes of about 1 to 2 mu m just before the gel point. The evolution of clusters is described by a simple model based on a stochastic method. Catalytically active materials can be prepared by anchoring metal colloids within the polymer particle network.