SEEDED LATEX POLYMERIZATIONS - STUDIES ON THE PARTICLE GROWTH-MECHANISM OF LATEX-PARTICLES

In order to clarify the particle growth mechanism of latex particles, we performed a series of seeded styrene latex polymerizations using minor amounts of isoprene to tag the newly generated polymers. Morphological studies of microtomed particles are presented. It was found that the monomer distribution within the particle was rather uniform. If the particle is larger than a critical value (approximately 0.15-0.20-mu-m), due to surface anchoring of the hydrophilic chain ends on the particle, the shell growth mechanism occurs. The polymerization takes place primarily in the shell region which is about the size of the end-to-end distance of the growing radicals (approximately 0.01-0.04-mu-m). For small latex particles (particle diameter < approximately 0.15-mu-m), a homogeneous reaction occurs inside the particles. Further evidence of the conversion data and molecular weight distributions also confirms the proposed shell growth mechanism.