The polymerization of styrene in oil-in-water microemulsions made with
the cationic surfactants dodecyltrimethylammonium bromide or chloride
is studied as a function of inorganic electrolyte (KBr, KCl, or K2SO4
) concentration. The resulting microlatex is stable, but as the electr
olyte concentration increases, both the average radius and the polymer
molecular weight decrease. The presence of electrolyte slows the poly
merization rate and diminishes final conversion as followed by gravime
try, dilatometry, and calorimetry. Both particle radius, determined by
quasielastic light scattering, and molecular weight show only Limited
growth as styrene conversion increases, suggesting continuous nucleat
ion of latex particles and termination by chain transfer to monomer. S
mall-angle neutron scattering (SANS) of undiluted parent and polymeriz
ed microemulsions shows that a unimodal population of swollen micelles
evolves into a bimodal population of empty micelles coexisting with l
arge polymer particles. Structural details of the parent and polymeriz
ed microemulsions as determined by SANS are used to assess nucleation
mechanisms previously proposed for emulsion polymerization.