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

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 degrees C for 60-90 min. Conversely, the azidation of poly(2,3,4,5,6-pentafluorostyrene) under similar conditions resulted in similar to 90% substitution efficiency. Azide-functional (co-)polymers were thermally stable below 100 similar to C and were subsequently modified with (i) four different alkynes (CuBr, triethylamine, DMF, 55 similar to 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 H-1 NMR, F-19 NMR, Fourier transform infrared spectroscopies, and size exclusion chromatography. Given their adaptability, perfluorophenylazides have huge potential as multipurpose intermediates in polymer and materials chemistry.