Phenyldiazomethane was found to be polymerized by the reaction with palladium-based initiating systems. Homopolymerization of phenyldiazomethane afforded a polymer, whose main chain consists of phenylmethylene framework (-CHPh-) and azo groups (-N=N-). The incorporation of the azo group was suggested from the results of elemental analyses, and confirmed by Raman spectroscopy. Palladium-mediated copolymerization of phenyldiazomethane with (E)-1-diazo-3-nonen-2-one or ethyl diazoacetate proceeded to give copolymers having phenylmethylene framework, azo group, and acylmethylene or ethoxycarbonylmethylene framework in the main chain, with a variety of their compositions. (c) 2006 Wiley Periodicals, Inc.