Intrinsically Proton-Conducting Benzimidazole Units Tethered to Polysiloxanes

Abstract

Polysiloxanes with pendant benzimidazole units have been prepared by free radical thiolene coupling reactions of 2-(2-benzimidazolyl)ethanethiol and vinyl-functional polysiloxanes. The latter polymers were prepared by anionic ring opening copolymerization of 1,3,5,7-tetramethyl-1,3,5,7tetravinylcyclosiloxane and 1,3,5-hexamethylcyclosiloxane. Copolymers with different degrees of benzimidazole functionality were conveniently obtained by varying the monomer ratios. The coupling reaction was found to be very efficient, and the vinyl groups were completely consumed, as confirmed by NMR and FTIR spectroscopy. The glass transition temperature (T g) of the benzimidazole functional copolymers increased dramatically with the benzimidazole content at low contents to reach a plateau value just above 50 °C at a content of approximately 33 mol % benzimidazole functional siloxane residues in the copolymer. Conductivity measurements carried out at 60 and 140 °C indicated that the level of polymer segmental mobility, and thus the Tg, was the most decisive parameter for the proton conductivity at low temperatures (60 °C), while the benzimidazole concentration was more important at elevated temperatures (140 °C). A conductivity of 7 × 10 -6 S/cm was reached at 140 °C by a polysiloxane carrying 57 mol % benzimidazolegrafted siloxane residues under completely anhydrous conditions.

Anhydrous Polymeric Proton Conductors Based on Imidazole Functionalized Polysiloxane

“…The resulting raw product was purified by column chromatography. (14) according to the general procedure the following amounts were used and converted: (8) (15) according to the general procedure the following amounts were used and converted: (10) (88.6 mmol), dichloromethylsilane (120 ml), methylenechloride (40 ml …”

“…The cyclic tetramers (n = 4) (23,24,25) were obtained from the precursors (14,15,16) according to Y. Takuma et al [45] following route A with THF as solvent in yields of nearly 100%.…”

“…The monomers (14,15,16) were dissolved in THF and deionized water, p-toluenesulfonic acid was added. After heating to reflux for 1h toluene was added and THF was distilled off rapidly.…”

“…to polymer backbones [11][12][13][14][15]. In this paper a detailed analysis of the properties of oligomeric and polymeric siloxanes with immobilized imidazole is presented.…”

Blend membranes based on sulfonated poly(ether ether ketone) and polysulfone bearing benzimidazole side groups for proton exchange membrane fuel cells

“…imidazole) attached to small, fixed chains have also been studied, but no fuel cell data are available [3,[12][13][14][15]. In addition, efforts have been made to tether heterocycles like imidazole, 1H-1,2,3-triazole, and benzimidazole to alkyl polymer chains [16][17][18][19][20], but they are not ideal for high temperature PEMFC due to the low proton conductivity and poor stabilities of the alkyl backbones.…”