Kinetics of the dispersion ring-opening polymerization of epsilon-caprolactone initiated with diethylaluminum ethoxide

Dispersion polymerization of epsilon-caprolactone initiated with diethylaluminum alkoxide, carried out in the 1,4-dioxane:heptane (1:9 v/v) mixture at room temperature in the presence of poly(dodecyl acrylate)-g-poly(epsilon-caprolactone) used as the surface active agent, proceeds in two stages. In the first stage the growth of the poly(epsilon-caprolactone) chains is initiated in solution and, when the molecular weight of growing macromolecules comes close to 1000, the primary particles are nucleated and all propagating chains become incorporated into growing microspheres. In the second stage the polymerization process consists of propagation taking place inside microspheres into which monomer molecules diffuse from solution. During the first stage the apparent propagation rate constant is low and does not exceed 1 x 10(-2) L . mol(-1). s(-1). In the second stage, due to the high local concentration of growing species confined in polymer particles, the apparent propagation rate constant becomes much higher. For monomer concentrations in the region from 3.9 x 10(-1) mol . L(-1) to 4.3 x 10(-1) mol . L(-1) and for initiator concentrations ranging from 3.4 x 10(-3) mol . L(-1) to 2.6 x 10(-2) mol . L(-1) the apparent propagation rate constant (k(p)(app)) varied from 4.79 x 10(-1) L . mol(-1). s(-1) to 6.5 x 10(-2) L . mol(-1). s(-1).