Semiconductor polymers are successfully implemented in a broad range of applications such as light emitting diodes, field effect transistors and photovoltaic devices. Most of the achievements reached in the development of these devices were obtained at experimental level, being difficult to identify individually the influence of each factor that limits and controls these devices efficiency. One of the factors that strongly influence the performance of polymer-based devices is the presence of chemical defects in the polymer strands that change their molecular properties. As a result, these polymer strands can work like traps or deep energetic states for charge transport, leading, for instance, to a decrease on charge mobility. At experimental level it is a difficult task to isolate the influence of each type of chemical defects individually on the molecular properties of the polymer strands. It is in this context that theoretical modelling seems to be the most suitable approach to get a deep understanding of the influence of chemical defects on the molecular properties of semiconductor polymers. By performing quantum molecular dynamics calculations we study the influence of chemical defects on the molecular properties of poly(para-phenylenevinylene) (PPV). Our results show clearly a significant difference on the electronic properties of defective polymer strands (e.g. charge carrier localization, ionization potential, electron affinity and electric-field threshold for charge carrier mobility along the polymer backbone) as compared with defect-free strands.