EFFECTS OF THE INITIATOR TYPE ON THE DISPERSION COPOLYMERIZATION OF POLY(ETHYLENE GLYCOL) MACROMONOMER AND STYRENE

The dispersion copolymerization of methacryloyl terminated poly(ethylene glycol) (MMA-PEG) macromonomer and styrene initiated by a water- and oil-soluble radical initiator was investigated by a conventional gravimetric method at 60-degrees-C. The rate of polymerization and number of radicals per particle were found to decrease with conversion and decrease was more pronounced with the oil-soluble initiator. On the other hand, the size, number of particles and molecular weight of polymers increased with conversion and increase was more pronounced with the water-soluble initiator. The experimental data indicate that the formation of radicals in the continuous phase plays a dominant role in the growth of polymer chains and polymer particles. The distribution of the oil-soluble initiator between continuous and monomer/polymer phases leads to the generation of radicals also in the monomer/polymer phase and to the increased termination events. The generation of radicals and the termination of growing radicals in polymer particles are promoted through the cage effect mechanism.