We have prepared two xanthate precursor polymers (6) and one sulfinyl precursor oligomer (7). In this way the polymerization behavior of three xanthate-containing monomers (3, 4, and 5) was studied. The chemical modifications on the monomer stage allowed to evaluate the outcome of the polymerization in relation to the chemical structure of the monomer. Polymerizations were performed in dry THF at different temperatures. The thermal conversion to the conjugated PPV structure, as well as its stability, was studied with different analytical techniques such as in-situ FT-IR spectroscopy, in-situ UV-vis spectroscopy, thermogravimetric analysis (TGA), and direct insert probe mass spectroscopy (DIP-MS). By combining the information obtained from these techniques, we were able to obtain a very detailed picture about the elimination process. These measurements also confirmed the formation of cis double bonds in xanthate precursor polymers on conversion. However, subsequent cis-trans isomerization in the end leads toward an all-trans-PPV polymer.