Polymerization within styrene emulsion droplets

Abstract

The kinetics, particle-size distributions and molecular-weight distributions of styrene emulsion polymerization systems containing small amounts of a long-chain alcohol have been studied. The emulsion droplets in such systems were ca. 0.1 µm in radius (of similar size to latex particles formed in conventional emulsion polymerizations). Under suitable conditions, the locus of polymerization was found to be within the monomer droplets, rather than outside the droplets as in conventional systems, in conformity with the proposal of Ugelstad and coworkers. Mathematical modelling of the kinetic data shows that the rate coefficient for entry of free radicals into the droplets is significantly less than that found for ordinary latex particles; this explains why the rate of polymerization in systems where polymerization occurs in the droplets is relatively slow. One possible explanation for this low capture efficiency could be the relative difficulty of displacement of surfactant molecules by the incoming oligomeric free radicals.