Styrene polymerization in oil‐in‐water microemulsions: kinetics of polymerization

Microemulsion polymerization of styrene was carried out in water, hexadecyltrimethylammonium bromide or sodium dodecyl sulfate, and butyl carbitol (system. name: 2‐(2‐butoxyethoxy)ethanol) using water‐soluble potassium peroxodisulfate (KPS) or oil‐soluble 2,2′‐azoisobutyronitrile (AIBN) as initiator. The latexes have been stable for one year. The effects of temperature, initiator and monomer concentrations on the polymerization kinetics were investigated. The polymerization rates were measured by dilatometry and show two stages (nucleation and growth). A longer nucleation period was found in the polymerization initiated by KPS as compared to AIBN. The initial polymerization rate varied with the 0,47 power of KPS concentration and the 0,39 power of AIBN concentration. The activation energy of the polymerization was found to be relatively low (ca. 50 kJ/mol) for the system initiated with AIBN and about 90 kJ/mol for the KPS‐initiated system. Molecular weights of polystyrene of several millions were obtained in all cases, especially for systems initiated with AIBN. The latex particles were nearly spherical with an average particle diameter of about 25 nm. The mechanism of polymerization in the oil‐in‐water microemulsion is discussed.