MACROGELATION OF POLY(ACRYLIC ACID) DISPERSIONS THROUGH CROSS-LINKING

The reaction of poly(acrylic acid) dispersions with diglycidyl ether o r dicarboxylic dichlorides as crosslinking agents leads to the formati on of macrogels without shrinking of the original dispersions. The par ticles of the dispersion are stabilized by block copolymers and are ab out 100 nm in diameter. Micrographs of scanning electron microscopy of the freeze-dried gel show a three-dimensional network structure forme d by the particles. The kinetics of the crosslinking reaction was stud ied by differential scanning calorimetry. A model is presented conside ring a partition equilibrium of the crosslinking agent between the dis perse and the continuous phase and the influence of mass transport of the crosslinking molecules in the interior of the particle. By means o f dynamic rheology it was shown that the macrogels obtained are the re sult of chemical crosslinking reactions between the particles. Frequen cy-dependent measurements of the dynamic modulus during the crosslinki ng reaction showed that the network formation is a reaction-controlled cluster-cluster aggregation process. Dynamic light scattering experim ents indicate a dominating cluster fraction with sizes of about 1 to 2 mu m just before the gel point. The evolution of clusters is describe d by a simple model based on a stochastic method. Catalytically active materials can be prepared by anchoring metal colloids within the poly mer particle network.