Chemically Stable Sulfonated Polytriazoles Containing Trifluoromethyl and Phosphine Oxide Moieties for Proton Exchange Membranes

Abstract

Polytriazoles are considered as an excellent high-performance polymer due to their outstanding set of properties. The current investigation reports the synthesis of a phosphorus-containing fluorinated diazide monomer, that is, bis[4-(4′-azidophenoxy)-3-trifluoromethyl phenyl] phenylphosphine oxide (PFAZ) and utilization of this compound to synthesize a set of trifluoromethyl groups and phosphine oxide containing sulfonated polytriazoles (PTPFBSH-XX). The copolymers with a different level of sulfonation (-XX = −60, −70, −80, −90) were prepared by the Cu(I) catalyst-assisted click reaction of equimolar amounts of a dialkyne (BPALK) and a mixture of diazides having one sulfonated diazide (DSAZ) and PFAZ. The polymers were further characterized by NMR ( 1 H, 13 C, 19 F, and 31 P) and FTIR spectroscopy. Freestanding membranes were attained from the dissolved copolymers solution in DMSO by standard solution casting route. The membranes showcased acceptable thermal and mechanical stabilities, excellent water management with a high proton conductivity, and outstanding oxidative stability. SAXS, TEM, AFM, and cross-sectional FE-SEM studies of the membranes indicated phase-separated morphology. The oxidative stabilities of the membranes ranged over 18 h. The polytriazole PTPFBSH-90 (PFAZ/DSAZ/BPALK = 10:90:100, where the degree of sulfonation is 90%) having a weight-based ion exchange capacity (IEC W ) of 2.39 mequiv g −1 exhibited a high proton conductivity of 142 mS cm −1 under hydrated conditions at 90 °C. Furthermore, PTPFBSH-XX polymer membranes displayed a comparable performance in microbial fuel cell as Nafion117. The chemical oxygen demand removal results indicated that the polymeric membranes could be sustainable in bioelectrochemical systems.

Preparation of Sulfonated Polytriazoles with a Phosphaphenanthrene Unit via Click Polymerization: Fabrication of Membranes and Properties Thereof

“…All other chemicals were used without additional purification. The compounds 4,4′-(propane-2,2′-diyl)­bis­((prop-2-ynyloxy)­benzene) (bisphenol-based dialkyne (BPALK)) and 1,1-bis-(4-aminophenyl)-1-(6-oxido-6 H -dibenz⟨ c , e ⟩⟨1,2⟩oxaphosphorin-6-yl) ethane (DPA) were prepared according to reported procedures. , …”

“…In light of such interesting chemistry, some sulfonated copolytriazoles have been synthesized effectively by CuAAC-type click polymerizations of terminal diazides and dialkynes, and their PEM-related studies have been reported. The aromatic nature of the triazole ring provided oxidative and hydrolytic stability, and the basic nitrogen sites functioned as proton charge carriers by accepting protons from the sulfonic acid part. , Moreover, the sulfonated copolytriazoles with the phosphine oxide moiety showed encouraging results in dimensional stability, water management, proton conductivity, and oxidative stability compared to numerous other polymers. , In these types of highly conductive polytriazoles, a unique kind of proton-conducting channels was created by hydrogen bond formation among the sulfonic acid (−SO 3 H), phosphine oxide (−PO), and triazole rings. , …”

“…Simultaneously, this bulky unit created large free-volume cavities to accommodate more water molecules without much swelling of the polymer membranes . Additionally, the electron-withdrawing ability of −PO of the DOPO unit enhances the oxidative stability of the polymer chains. , A few DOPO unit-based polymers have been reported in the areas of epoxy resin, polyamide, and polyimide for flame retardancy and gas transport applications. , Nevertheless, so far, no DOPO moiety comprising polytriazoles has been reported. Hence, in view of the advantageous effect of the DOPO unit, it could be beneficial to synthesize polytriazoles with DOPO units.…”

“…Accordingly, the DOPO moiety comprising the diazide compound 1,1-bis-(4-azidophenyl)-1-(6-oxido-6 H -dibenz⟨ c , e ⟩⟨1,2⟩oxaphosphorin-6-yl) ethane (DPAZ) has been synthesized and utilized to synthesize several novel polytriazoles (PTDPB and PTDPBS- XX , where XX denotes the molar percentage of the sulfonated diazide in the diazide mixtures). The polymers were well-characterized spectroscopically by Fourier transform infrared (FTIR) and NMR techniques, and the membranes were fabricated and their properties were investigated to assess their suitability in PEM application compared to similar polytriazole membranes reported earlier. , Besides, the microbial fuel cell (MFC) performance of sulfonated copolytriazoles has been explored to obtain an idea of the suitability of membranes in bioelectrochemical systems.…”

Structural architectures of polymer proton exchange membranes suitable for high-temperature fuel cell applications

“…Various membrane materials have been applied to PEMs [20, 44,54]. Thermally stable polymers with -SO 3 H groups in the main and side chains have been widely employed as PEMs because of their high proton conductivities and easy modification [20, [55][56][57]. Sulfonated polymers are generally amphiphilic.…”