Nitroxide mediated styrene radical polymerization using a fluorescence marked mediator

Polystyrenes containing fluorescence end-groups were prepared by nitroxide-mediated radical polymerization. Combined molar mass regulator contained besides alkoxyamine part the structure of fluorescence mark. Stable nitroxyl radical represented 2,2,6,6-tetramethylpiperidine-Noxyl and covalently bonded fluorescence mark was benzothioxanthene. A fluorescence method as well as UV absorption was employed for measuring the concentration of nitroxyl-terminated chains in polystyrene samples. Theoretical molar masses of polystyrenes were calculated from these concentrations on the assumption that all polystyrene chains are terminated by alkoxyamine dormant end-functionality bearing fluorescence probe. Comparisons of these data with the molar masses from GPC gave us the range of the marked active polymer chain ends. Fractions of active polymer chain ends depended on the conversion. With increased conversion the fraction of polystyrene chains terminated by alkoxyamine was decreased. From this follows that the "livingness" of polymerization process decreased with the increasing of conversion. It should result in higher extent of termination and subsequently in the increasing of polydispersity with increased conversion. Despite this the observed polydispersity was the same for all conversion and reached the value ca. 1.3. The changing viscosity is responsible for the constant polydispersity. (C) 2009 Elsevier Ltd. All rights reserved.