MECHANISM OF PARTICLE FORMATION AND KINETICS OF THE DISPERSION POLYMERIZATION OF CYCLIC ESTERS

Pseudoanionic and anionic polymerizations of epsilon-caprolactone and lactides in 1,4-dioxane:heptane mixtures containing poly(dodecyl acryl ate)-g-poly(epsilon-caprolactone) yield polyesters in form of microsph eres. Monitoring partition of active centers between solution and micr ospheres revealed that particles are formed during initial period, whe n macromolecules reach their critical masses (ca. 1 000) and became in soluble. Then, propagation proceeds inside of microspheres into which monomer diffuses from solution. Monitoring of variation of the number of particles in a unit volume of reaction mixture with time indicated that after a primary nucleation the delayed nucleation and aggregation are absent. In effect, microspheres with narrow diameter distribution are obtained. Kinetic measurements revealed that in the dispersion ps eudoanionic (initiator (CH3CH2)(2)AlOCH2CH3) and anionic (initiator (C H3)(3)SiONa) polymerizations of epsilon-caprolactone the overall rates of monomer conversion are from 10 to 30 times higher than for the cor responding polymerizations in solution (THF solvent). Analysis of kine tic equations indicated that the observed faster monomer conversions i n polymerizations in dispersed systems are due to the high local conce ntrations of active centers and monomer in growing microspheres.