Poly(ADP-ribosylation) is a post transductional modification that regulates protein's function. Most of the proteins subjected to this control mechanism belong to machineries involved in DNA damage repair, or DNA interacting proteins. Poly(ADP-ribose) polymers are long chains of even 100 monomer length that can be branched at several positions but, notwithstanding its importance, nothing is known concerning its structure. In order to understand which are the geometrical parameters that confer to the polymer the structural constraints that determine its interaction with the target proteins, we have performed molecular dynamics of three chains of different length, made by 5, 25 and 30 units, the last one being branched. Analysis of the simulations allowed us to identify the main intra- and inter-monomer dihedral angles that govern the structure of the polymer, that however doesn't reach a unique definite conformation.