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John Battiste '90, Alex Lohse, and Babu Gaddam, 3M

Controlled/living radical polymerizations are a facile way to make polymers of well-defined architecture for advanced applications. However, photo-initiated living polymerizations are not as common commercially, as say anionic polymerizations, due to lingering non-ideal behavior of many initiator systems. We have used NMR spectroscopy to follow the fate of many mono- and di-functional xanthate and dithiocarbamate initiators in the polymer chain. The NMR analysis included consumption of the initiator, MW as a function of conversion, and end group analysis to determine the kinetics for initiation of polymer chain growth in the second direction for di-functional initiators. From the end group  analysis, some undesired side reactions were also identified. Preliminary studies were done with aliquots taken from the polymerization at different times. This procedure is tedious, and it is difficult to adequately space the time points without prior knowledge of the kinetic rates. In order to obtain more detailed kinetic profiles, an in-situ setup was developed using a 365 nm LED light source with a fiber optical cable to directly irradiate the sample in the NMR spectrometer while acquiring data. Using the in-situ NMR characterization, detailed kinetic rates were obtained for several initiators to evaluate the fidelity of the living radical process. A number of parameters were varied including UV intensity, temperature, and %solids to assess their impact on the kinetic profiles and undesired side reactions.