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39855-GB7
Synthesis and Characterization of Vinyl-Aromatic Polymers Containing Photochemically Active Groups
In our previous reports, we have used atom transfer radical polymerization as means to grow polymer chains using 9-bomofluorene or photodimers of 9-haloanthracenes as initiators. Both of these projects have lead to multiple publications in peer-reviewed journals, most recently being a Polymer Bulletin paper outlining the effect of the bridgehead halogen on the anthracene photodimer system.
Our current work is focused back on the fluorene-labeled polymers. We have been working on a method that will allow us to grow two chemically distinct polymer chains from the 9-position of the fluorene unit by anionic and controlled radical polymerization performed sequentially, ideally leading to polymer grafted polyfluorenes. Attempts to use 9-bromofluorene as an anionic initiator, by reaction between 9-bromofluorene and a strong base, have failed due to the susceptibility of the C-Br bond to heterolytically break once the fluorenyl anion is formed, leading to carbenes which couple to give fluorene dimers with C-C double bonds between the groups. This has motivated us to replace the bromine with an alkoxy group, giving us a potential initiator for nitroxide mediated polymerizations (NMPs) while still retaining the acidic 9-H on the fluorene. Initial results show that this fluorene-based alkoxyamine can indeed act as an intiator in NMP, yet we have been unable to use it in anionic polymerizations via deprotonation of the 9-H prior to the NMP reaction. We are currently looking at improved methods of purifying the alkoxyamine, as we believe small amouns to impurities remaining after its workup may play a role in the inability to form the fluorenyl anion.
