Unexpected reactions associated with the xanthate-mediated polymerization of N-vinylpyrrolidone
The monomer N-vinylpyrrolidone (NVP) undergoes side reactions in the presence of R group functional xanthates and impurities. The fate of the monomer NVP and a selection of six O-ethyl xanthates during xanthate-mediated polymerization were studied via NMR spectroscopy. A high number of by-products were identified. Significant side reactions affecting NVP include the formation of an unsaturated dimer and hydration products in bulk or in solution in C 6D6. In addition, the xanthate adjacent to a NVP unit was found to undergo elimination at moderate temperature (60-70°C), resulting in unsaturated species and the formation of new xanthate species. The presence of the chlorinated compound α-chlorophenyl acetic acid, ethyl ester, a precursor in the synthesis of the xanthate S-(2-ethyl phenylacetate) O-ethyl xanthate, resulted in a dramatic increase in the rate of side reactions such as unsaturated dimer formation and a high ratio of unsaturated chain ends. The conditions for the occurrence of such side reactions are discussed in this article, with relevance to increasing the control over the polymerization kinetics, endgroup functionality, and control over the molar mass distribution. © 2008 Wiley Periodicals, Inc.