Bifluoride-catalysed sulfur(VI) fluoride exchange reaction for the synthesis of polysulfates and polysulfonates

Abstract

Polysulfates and polysulfonates possess exceptional mechanical properties making them potentially valuable engineering polymers. However, they have been little explored due to a lack of reliable synthetic access. Here we report bifluoride salts (Q⁺[FHF]^-, where Q⁺ represents a wide range of cations) as powerful catalysts for the sulfur(VI) fluoride exchange (SuFEx) reaction between aryl silyl ethers and aryl fluorosulfates (or alkyl sulfonyl fluorides). The bifluoride salts are significantly more active in catalysing the SuFEx reaction compared to organosuperbases, therefore enabling much lower catalyst-loading (down to 0.05 mol%). Using this chemistry, we are able to prepare polysulfates and polysulfonates with high molecular weight, narrow polydispersity and excellent functional group tolerance. The process is practical with regard to the reduced cost of catalyst, polymer purification and by-product recycling. We have also observed that the process is not sensitive to scale-up, which is essential for its future translation from laboratory research to industrial applications.

Figure 1. Catalyst screening for the SuFEx-based synthesis of polysulfates

a, The synthesis of P-1 from monomers A-1 and B-1 is employed as a model reaction for catalyst screening. b, Control experiments with DBU or BEMP as catalysts. c, Evaluation of K⁺[FHF]⁻ (with/without phase transfer reagents) as the catalyst with a reaction time of 17 h. d, Evaluation of onium bifluoride (Q⁺[FHF]⁻) salts as catalysts. e, Evaluation of poly(hydrogen fluoride) salts as catalysts. NMP, N-methyl-2-pyrrolidone; TBS, tert-butyldimethylsilyl; M_n^ps, number-average molecular weight with polystyrene as standard; PDI, polydispersity index.

Figure 2. Two alternative strategies for the synthesis of polysulfates via the bifluoride-catalysed SuFEx reaction

a, The synthesis of P-1 from the bifunctional monomer AB-1. b, The synthesis of P-1 from the polycondensation of A-1 with sulfuryl fluoride gas (SO₂F₂). c, The synthesis of P-7 from the polycondensation of A-7 with sulfuryl fluoride gas (SO₂F₂). NMP, N-methyl-2-pyrrolidone; TBS, tert-butyldimethylsilyl; M_n^ps, number-average molecular weight with polystyrene as standard; PDI, polydispersity index.

Figure 3. Catalysts preparation and bulk synthesis of P-1

a, Reported procedure for the preparation of catalyst Q-5. b, A schematic protocol for the preparation of bifluoride catalysts via the ion-exchange reaction of onium halides (Q⁺X⁻, X = Cl, Br, I) with anhydrous hydrogen fluoride (see Supplementary Section 2-3-6 for details). c, The 100-gram scale preparation of P-1 from the polycondensation of A-1 (0.2 mol) and B-1 (0.2 mol) catalysed by 0.05 mol% of Q-5 in NMP (50 ml). d, 112.7 g P-1 was obtained from bulk polymerization (M_n^ps = 110 kDa, PDI = 1.7). e, 49.1 g TBSF was recycled from the bulk polymerization process.