On the role of initiator in emulsion polymerization

The use of nonionic poly(ethylene glycol)-azo-initiators instead of ionic initiators in emulsion polymerizations offers interesting possibilities for modifying the colloidal and polymeric properties of polymer dispersions. Experimental results are presented for various kinds of anionic, cationic, and nonionic stabilizers as well as for peroxodisulfate initiators with different counter ions (ammonium and potassium). For example, in a styrene emulsion polymerization (with monomer to water mass ratio of 1:4 at a given concentration of 1% with respect to monomer mass of either an anionic or a cationic surfactant), the replacement of either peroxodisulfate or 2,2'-azobis(2-amidinopropane)dihydrochloride by a poly(ethylene glycol)-azo-initiator (with a poly(ethylene glycol) molecular weight of 200 g mol^-1) leads to particles with considerably smaller size, polymers with higher molecular weight, and latexes with higher viscosity.