A monomer 3,4-(2-methylene)propylenedioxythiophene (MProDOT) was synthesized and electrochemically polymerized to yield PMProDOT with methylene groups that have the potential to be further functionalized. Electrochemical redox switching of PMProDOT between -0.6 and +1.5 V (vs Ag/Ag+) caused the cross-linking reaction between methylene moieties at the anodic potential limit and resulted in the fast decrease of electroactivity due to destruction of pi-conjugation. When PMProODT was subjected to +1.5 V in the presence of styrene (ST) monomers, the loss of electroactivity was not significant and the mass of the PMProDOT was rapidly increased. The mass increase was ascribed to polystyrene (PST) grafting onto PMProDOT. Simultaneous oxidation of methylene groups and ST at +1.5 V led to the coupling of ST to PMProDOT, which reduced cross-linkable free-methylene moieties. PST-grafted PMProDOT showed relatively stable electroactivity over repeated potential cycling. The infrared spectrum of PST-grafted PMProDOT also showed additional sp(2) C-H stretching peaks possibly due to PST grafting. (C) 2008 The Electrochemical Society.