Efforts are made to identify the irregular structures formed in poly(phenylene-vinylene) (PPV), obtained via the conversion of its sulfonium precursor by different physical and chemical methods. Analysis by X-ray photoelectron spectroscopy and Fourier transform infra-red spectroscopy reveals that the ketone structure is a common defect appearing in PPV whenever the conversion is carried out in the presence of oxygen. In contrast to the PPV obtained by pyrolysis of the precursor, the PPV obtained by treatment of the precursor with H2SO4 contains no chlorine residue but much more sulfur residue. Ion bombardment of the sulfonium precursor leads to a PPV containing no trace of sulfur or chlorine in the structure. Finally, the nature of bonding between the carbon atom and oxygen, chlorine or sulfur atoms in PPV is discussed and irregular structures are proposed.