Dispersion polymerization of dilactide and ε-caprolactone
Polimery 2002, No 7/8, 485
Ring-opening polymerization of dilactide and ε-caprolactone carried on in 1,4-dioxane — heptane mixed solvent in the presence of poly(dodecyl acrylate)-g-poly(ε-caprolactone) surface active agent led to formation of polyesters shaped into microspheres with diameters from 0.6 to 7.4 mm and with small diameter polydispersity factor (Dw/Dn). Studies of the mechanism of particle formation revealed that all growing chains became incorporated into microspheres at the very beginning, when monomer conversion was low (£10%) and that the number of the initially formed microspheres did not change with time. Thus, subsequent monomer additions resulted in increasing volumes of particles without affecting their number in suspension. It has been found also that in the polymerization of dilactide the average number of propagating macromolecules per microsphere was independent from the mitial initiator concentration and the increased initiator concentration resulted in increased number of particles. This observation conformed to the model illustrating formation and growth of microspheres according to which new particles are formed by collision of two polyester chains with molecular weight exceeding the critical ones and subsequently other chains are incorporated into existing particles by accretion. Thus, by selection of the required initial initiator and total monomer concentration (introduced in one or in more steps to the polymerizing mixture) it was possible tailoring of particle concentration and particle diameters.
Keywords: dispersion ring-opening polymerization, dilactide, ε-caprolactone, microspheres formation, microspheres diameter, diameter polydispersity factor