Bulk Polymerisation Of Polyurethanes

The objective of this work was to investigate aspects of the heterogeneous polymerization reaction of two components of a typical polyurethane formulation. A review of the scientific literature together with general isocyanate chemistry is given. The heterogeneous reaction between these components was found to be sensitive to changes in dispersed droplet size as well as temperature and amount of catalyst added. A study to evaluate the site of the chemical reaction, when these components are mixed heterogeneously indicated that the isocyanate components form droplets in the continuous hydroxyl component phase. As the reaction proceeds it was discovered that the dispersed droplets of the isocyanate component became encapsulated in the polyurethane product. It was also found that further reaction required the diffusion of the hydroxyl component through this product layer in. order to reach the site of the chemical reaction, the polymer/isocyanate interface. Models for this proposed reaction scheme were to prové useful in the description of the reaction parameters. Two approaches to the diffusion of the hydroxyl component through the product layer were investigated. These included that in which this component was considered to diffuse by a steady state diffusion manner. The other approach considered the diffusion of the hydroxyl component through the product interface by a non-steady state diffusion manner. The second order rate constant calculated from the model parameters for the heterogeneous reaction was found to be greater than that for the corresponding reaction in which the components were combined homogeneously. The activation energies calculated for the two above cases were found to be similar, indicating that the difference in the rate constants observed is due to a change in the pre-exponential factor of the Arrhenius equation. In agreement with the theories cf the model it was possible to influence the stability of the reaction components with respect to flocculation using additives introduced into the hydroxyl component. Two specific additives were found, by a novel turbidity method, to influence the stability. One of these was the commercially available LK221 and the other was synthesised in the laboratory. In order to successfully investigate the stability to flocculation induced into the system by these additives, the theories relating particle size to turbidity were adapted to account for the reaction between the polyurethane components.