The electroactivity of monomeric species is higher than polymeric ones. During the CV cycles, the concentration of monomeric species decreases. Polymeric species give redox reactions harder than monomeric species and thus, the electron transfer reactions of polymeric species can shift more positive potentials if the electropolymerization process is oxidative whereas if it is on the cathodic area, electrochemical reaction of polymeric species occurs on more negative potentials. Moreover, on the increasing number of cycles, the polymeric species may not show any redox process because electroactivity of polymer materials is low.

The impedance[1] of the WE increases over cycle due to the advancement of the electro-polymerization mass. The main mode[2] is due to the increase of the polymer's thickness (on the WE).

1. If EIS is available you can verify it.

2. The fast initial mode (first few cycles) might appear as the surface covering mode of the WE.

Well.

It depends on your monomer....

If it is a π-conjugated system, its oligomer and polymer are oxidized easier than the correspondent monomer, due to π-electrons' delocalization. In some cases, the polymer overoxidation potential may be equal and even lower than the monomer polymerization potential, leading to the irreversible changes in the polymer morphology (see "The polythiophene paradox").

What is the monomer you're using?

The obvious potential shift of the wave current

maximum provides information about the increase in the electrical

resistance in the polymer film and the overpotential needed

to overcome the resistance，You can also have a look of one of my articles where the same phenomenon occurred to me:Analytica Chimica Acta 805 (2013) 87– 94；Sensors and Actuators B 171– 172 (2012) 786– 794

Thank you everyone. the answers are complete and useful.