KINETICS AND PARTICLE FORMATION IN THE PR ECIPITATION POLYMERIZATION OF ACRYLIC-ACID IN THE PRESENCE OF POLYSTYRENE-BLOCK-POLY(ETHYLENE OXIDE) COPOLYMERS

A surfactant system containing polystyrene-block-poly(oxyethylene) and water was used for the free radical precipitation polymerization of a crylic acid in toluene. The use of this stabilizing system makes it po ssible to produce poly(acrylic acid) dispersions with a particle diame ter ranging from 50 to 300 nm and solid contents up to 40 wt.-%, which remain stable for months. The rate of polymerization, which was measu red on-line in a reaction calorimeter shows a strong autocatalytic beh avior. The maximum of the polymerization rate and the corresponding ti me of appearance depend strongly on the water content. The influence o f the composition of the surfactant (block length), its concentration and the concentration of initiator and monomer on the polymerization r ate and the particle diameter were studied. Especially by varying the block length of the copolymer, the number of particles, respectively t he particle diameter, can be controlled. To describe the course of the polymerization process, a model based on the theory of homogeneous pa rticle nucleation is suggested. The influence of water on the swelling equilibrium of the poly(acrylic acid) particles is taken into account .