SHELL GROWTH-MECHANISM IN EMULSIFIER-FREE EMULSION POLYMERIZATION - MORPHOLOGICAL AND KINETIC-STUDIES

For systems of emulsifier-free emulsion polymerization having particle diameter (D(p)) greater than 0-15-0.2 mum, a shell-growth mechanism for particle growth was proposed. According to the mechanism, the polymeric radicals can propagate only within the shell region having.a thickness about equal to the most probable end-to-end distance of the terminated polymer. This mechanism was considered to result from anchoring of hydrophilic ends of the growing radicals on the particle surface and from a high average number of radicals per particle. The occurrence of limiting conversion for such large particles was attributed to the consequence of shell-region polymerization characteristic of large emulsion particles and a monomer-diffusion-controlled polymerization mechanism within the particles during the high conversion period.