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Azide–para-Fluoro Substitution on Polymers: Multipurpose Precursors for Efficient Sequential Postpolymerization Modification

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journal contribution
posted on 10.04.2019, 12:44 by Janina-Miriam Noy, Yuman Li, Willi Smolan, Peter J. Roth
The 2,3,4,5,6-pentafluorobenzyl group has become a popular reactive functionality in polymer chemistry because of its high susceptibility to para-fluoro substitution with thiols. Herein, it is demonstrated postpolymerization that the para-fluoride can be substituted using sodium azide and that the resulting 4-azido-2,3,5,6-tetrafluorobenzyl-functional polymers are versatile precursors for a multitude of onward modifications with click-like efficiencies. Quantitative azide–para-fluoro substitution was found for poly­(2,3,4,5,6-pentafluorobenzyl methacrylate) and the related Passerini ester–amide (meth)­acrylic (co)­polymers when heated in DMF with sodium azide to 80 °C for 60–90 min. Conversely, the azidation of poly­(2,3,4,5,6-pentafluorostyrene) under similar conditions resulted in ∼90% substitution efficiency. Azide-functional (co-)­polymers were thermally stable below 100 °C and were subsequently modified with (i) four different alkynes (CuBr, triethylamine, DMF, 55 °C, overnight) to give 1,4-substituted 1,2,3-triazoles in >95% conversions; (ii) potassium thioacetate (DMF, RT, 15 min) with quantitative amidation to the acetanilide derivative; and (iii) dl-dithiothreitol (methanol/DMF, RT, 90 min), resulting in complete reduction of the azides to primary amines, which were subsequently acylated with two different acyl chlorides. Products were characterized by 1H NMR, 19F NMR, Fourier transform infrared spectroscopies, and size exclusion chromatography. Given their adaptability, perfluorophenylazides have huge potential as multipurpose intermediates in polymer and materials chemistry.