The synthesis and radical polymerization of an 18-e cobaltocenium vinyl monomer, 2 acryloyloxyethyl cobaltoceniumcarboxylate hexafluorophosphate (AECoPF(6)) are reported The side chain cobaltocenium-containing polymer, poly(acryloyloxyethyl cobaltoceniumcarboxylate hexafluorophosphate) (PAECoPF(6)), is a water soluble hydrophilic polyelectrolyte Through an effective ion-exchange process, this polymer was transformed into a hydrophobic poly(acryloyloxyethyl cobaltoceniumcarboxylate tetraphenylborate) (PAECoBPh(4)) polymer soluble in strong polar solvents such as dimethylformamide and dimethyl sulfoxide Electrochemical studies showed that both polymers have reversible redox processes in dimethylformamide These polymers exhibited high thermal stability