By using selectively C-13-labeled sulfinyl and Gilch polymers, only noneliminated groups were demonstrated to be present in significant amounts (ca. 6.9%) in the sulfinyl conjugated OC1C10-PPV. By means of a two-step elimination procedure, this amount could be reduced to a level less than 0.5%. In the Gilch route on the other hand, a tolane-bisbenzyl unit was confirmed to be the main structural defect. Furthermore, noneliminated groups were clearly present. For both polymerization routes no indications for other types of defects such as cross-links or branching, were detected while strong indications for carbonyl type end groups were found. The nature of all "defects" was elucidated by applying liquid 1D and 2D NMR spectroscopy and the amount was calculated based on fully quantitative C-13 NMR spectra.