AbstractThe rate of polymerization of vinyl acetate in systems containing poly(vinyl acetate) seed particles was investigated. A significant reduction in rate was observed when nonionic surfactants were adsorbed onto the particles prior to polymerization. The molecular weight of the poly(ethylene oxide) moieties in the surfactants was varied over two decades. The diminution in rate was relatively insensitive to this molecular weight variation, at least for higher molecular weights (≥20,000). A minimum in the rate was apparent at lower molecular weights. No new nucleation was detectable in any of these systems. The results have been interpreted in terms of two properties of the dissolved poly(ethylene oxide) layers through which the oligomeric free radicals must diffuse in order to reach the major loci of polymerization inside the particles. These two properties, the effective thickness of the dissolved poly(ethylene oxide) layer and its average microscopic viscosity, are expected theoretically to be approximately self‐compensating when the molecular weight is var