Exploring the limits of particle size for nanolatexes produced via monomer-starved semicontinuous emulsion polymerization

Abstract

The minimum size achievable by semicontinuous monomer-starved emulsion polymerization has been explored. Styrene was used as the monomer, and potassium persulfate and sodium dodecylsulfate were used as initiator and surfactant, respectively. The rate of monomer addition (Ra), surfactant concentration ([S]) and reaction temperature (T) were varied. The variations in the number of particles (Np) with these variables were confined to the equation Np=k(as[S])RI2/3Ra-2/3, if micelles were fully depleted by the end of monomer addition. However, the particle number approached a plateau at very low Ra and high [S], and a maximum at a high T followed by a sudden fall. These features were attributed to the depletion of either monomer or radical prior to that of micelles. The conditions for achieving the minimum particle size were explored. Using extremely low Ra, particles with diameter close to the size of micelles were detected in the early stage of reactions, which only grew a little with time. Under such conditions, it is possible to supress particle growth so that the average size of particles remains close to that of micelles.