Communication: The propagation rate coefficient (k(p)) of methyl methacrylate has been measured in miniemulsions. The molecular weight distributions show many higher order peaks which seems to be specific for pulsed initiation polymerization in compartmentalized liquids. The k(p) values are ver similar to bulk values although a frequency dependence is observed. This frequency dependence, which was overlooked in earlier research, is also present in pulsed laser experiments in bulk.