Polybenzimidazoles blends, sulfonated polymers

Kosmala, B. and Schauer, J. 2002. Ion-exchange membranes prepared by blending sulfonated poly(2,6-dimethyl-l,4-phenylene oxide) with polybenzimidazole. Journal of Applied Polymer Science 85 1118-1127. 

To prepare new and inexpensive membranes, various trials have been made 196 sulfonated aromatic polyether membrane such as polyether ketones (PEEK),197 sulfonated polysulfone198 and membranes from sulfonated polyphenylene sulfide,199 phosphoric acid-doped polybenzimidazole, (PBI),200 polybenzimidazole having sulfonic acid groups,201 polybenzimidazole with phosphonic acid groups,202 a blend membrane of polybenzimidazole and sulfonated polysulfone,203 sulfonated phosphazene polymer.204... 

Polymer blends leading to high-end polymers, e.g. from sulfonated polymers (sPEEK - sulfonated polyether-etherketone, sPPSU - sulfonated polyphenyl-sulfone) combined with alkaline components (amine, imidazole, polybenzimidazole) The combination results in ionic cross-linked phases. Commercially available polymers can be modified by different sulfonation reagents. Another possibility is to combine different monomers based on block co-polymers. The conductivity can be controlled by the number of S03H groups due to the dependence of the water uptake from the number of groups ([23] and references cited therein). 

Kerres et al., among others, developed the acid-base blend membranes from sulfonated polymers and aminated or other basic polymers [98] and concluded that the protonation of the basic groups is incomplete if the base is too weak [99]. Very recently, Frutsaert et al. [70] synthesized novel polymers for the development of high temperature PEMFC membranes comprising a blend of s-PEEK and a fluorinated copolymer bearing imidazole functions as pendant groups. The extensive work on intermediate temperature fuel cell membranes are well reviewed in Chap. 4 of this book including polybenzimidazole as the basic component and sulfonated and phosphonated ionomers of either nonfluorinated or partially fluorinated backbones as the acidic component. 

The scope of the reviewed R D work is limited to intermediate-T acid-base blend membranes prepared by mixing polybenzimidazoles and sulfonated or phosphonated acidic polymers. Other membrane types, where the acid-base concept was used to improve their relevant... 

Membrane prepared by blending sulfonated polybenzimidazole (PBI) with Nafion polymer showed a conductivity of 0.032 S cm The methanol permeability of the composite membrane was found to be 0.82 x 10 cm s as compared to Nafion, which is around 2.21 x 10 cm s [22]. Addressing the problem of methanol permeation, a composite membrane of Nafion with polyvinyl alcohol (PVA) for direct methanol fuel cell has been reported. It is concluded that at the weight ratio of 1 1 in PVA and Nafion, the thin film-coated Nafion membrane exhibited low methanol crossover, and the membrane protonic conductivity could be improved by the sulfonation treatment [23]. Recently, Zaidi et al. [24] prepared composite membranes of PFSA ionomer with boron phosphate and showed the conductivity of 6.2 X 10-2 S cm-i at 120°C. 

Blends of sulfonated PS and sulfonated PPO have been described in several papers as offering a combination of high proton conductivity and low methanol permeability [104, 105]. Optimum conductivity was obtained with a 50/50 blend of the sulfonated polymers, with each having an identical ion exchange capacity [104]. The miscibility of the PS/PPO system appeared to be maintained with the blend of the sulfonated polymers. Polybenzimidazole (PBI) and polysulfone (PSF) are immiscible however, sulfonated PSF is miscible with PBI and showed utility in phosphoric acid based fuel cells operated upto200°C[106]. PEMs comprised of Nafion and a vinylidene fluoride-hexafluoropropylene copolymer blend were evaluated... 

Besides the covalent crosslinking, Kerres et al. investigated the properties of fuel cell membranes of ionicaUy crosslinked polysulfonic adds. This type of crosslinking was achieved by blending sulfonated poly(arylene ether sul-fone)s and poly(arylene ether ketone)s with basic polymers, such as polybenzimidazole, poly(ethylene imine), poly(vinyl pyridine), or amino functional-... 

Microcellular foaming, bimodal cell size distributions, and high open-celled contents of molecular composites of HT-polymers were reported by Sun et al. [33], investigating blends of a rod-like polymer polybenzimidazole with an aminated PSU and poly(phenyl sulfone) by using carbon dioxide as a blowing agent. The complex foaming behavior was related to phase separation within the otherwise... 

Hasiotis C, Deimede V, Kontoyaimis C (2001) New polymer electrolytes based on blends of sulfonated polysulfones with polybenzimidazole. Electrochim Acta 46 2401-2406... 

In the following, those publications dealing with synthesis and characterization of intermediate-T blend membranes from PBI basic polymers and sulfonated or phosphonated polymers utilized as acidic macromolecular cross-linkers in the blends are discussed. In Fig. 4.4, those polybenzimidazoles along... 

KatzfuB A, Krajinovic K, Chromik A et al (2011) Partially fluorinated sulfonated poly(arylene sul-fone)s blended with polybenzimidazole. J Polym Sci Part A Polym Chem 49 1919-1927... 

The typical MEA constmction has in its original form a symmetric layout. The core unit consists of the membrane. For HT-PEM MEAs, usually polybenzimidazole in several pol5mieric modifications like sulfonation, blending of the polymer with other polymers or additives to... 

The interaction forces between the acidic and basic blend component include electrostatic and hydrogen bridge interaction. The sulfonated poly(ethersulfones) and poly(etherketones) were combined both with commercially available basic polymers (e.g., polybenzimidazole Celazole (Celanese), poly(4-vinylpyridine), polyCethylene imine)), and with self-developed basic polymers derived from poly(ethersulfones) [47] and poly(etherketones), including polymers that carry both sulfonic and basic groups onto the same backbone [48]. A wide variety of acid-base blend membranes with a broad property range were obtained. The most important characterization results of the ionically cross-linked ionomer membranes are... 

C. Hasiotis, Q. Li, V. Deimede, J. K. Kallitsis, C. G. Kontoyannis, N. J. Bjerrum, Development and characterization of acid-doped polybenzimidazole/sulfonated polysulfone blend polymer electrolytes for fuel cells, J. Electrochem. Soc. 148(5) A513-A519 (2001)... 

Savinell and co-workers, [105-107], who have principally studied phosphoric acid doped polybenzimidazole (PBl). Similar systems have been reported by He and co-workers [108], who in addition report the conductivities of PBl based membranes doped with PTA and zirconium hydrogen phosphate [108], Acid-base interactions in entirely polymeric systems have been reported by Kerres and co-workers [102], who prepared and stndied several membranes prepared by blending polymers with acidic (snlfonated-PEEK, sulfonated polyethersulfone) and basic (polybenzimidazole, poly-vinylpyridine) characteristics. Selected acid-base polymer systems are discnssed in the following. 

In contrast to the Nafion-FEP system, in which the immiscibility of the polymer components is clearly shown in Fig. 14.8, greater compatibility of Nafion and polybenzimidazole (PBI) was expected due to acid-base interactions between imidazole nitrogens and sulfonic acid protons. PBI should function in such a system as a crosslinker (see Fig. 14.15), producing a reduction in membrane swelling and permeability by methanol. Although the idea of examining acid-base membrane blends in fuel cells is not new [9,11-13,30], little work has been carried out with Nafion. 

Trogadas and Ramani summarized the modification of PEM membranes, including Nafion modified by zirconium phosphates, heteropolyacids, hydrogen sulfates, metal oxides, and silica. Membranes with sulfonated non-fluorinated backbones were also described. The base polymers polysulfone, poly(ether sulfone), poly(ether ether ketone), polybenzimidazole, and polyimide. Another interesting category is acid-base polymer blend membranes. This review also paid special attention to electrode designs based on catalyst particles bound by a hydrophobic poly-tetrafluoroethylene (PTFE) structure or hydrophilic Nafion, vacuum deposition, and electrodeposition method. Issues related to the MEA were presented. In then-study on composite membranes, the effects of particle sizes, cation sizes, number of protons, etc., of HPA were correlated with the fuel cell performance. To promote stability of the PTA within the membrane matrix, the investigators have employed PTA supported on metal oxides such as silicon dioxide as additives to Nafion. 

In the last few years, high performance miscible polymer blends have attracted attention in the search for new materials at lower costs. Recently, two new families of high performance blends consisting of an aromatic polybenzimidazole and aromatic polyimides [1-3] and aromatic polyimides and polyethersulfone [4] have been reported. However, even though these blends appear to be miscible over the entire range of compositions, phase separation on heating above Tg is irreversible. This contribution describes the miscibility behavior in polyether-sulfone/polyimide PI 2080 and polyethersulfone/ polyimide XU 218 blends with and without solvents. 

Perfluorinated sulfonic acid polymers, such as Nafion membranes, were the most commonly used materials in practical systems for their high proton conductivity and extremely high oxidative stability. However, due to the poor dimensional stability, low mechanical properties of Nafion at high humidity and high temperature, and high cost, an essential need for cost-effective and reinforced substitutes with improved performance arises [193-195]. Nafion blended with the second component could not only reduce the cost, but also improve the mechanical properties and the dimensional stability. Recently, the reinforced composite membranes based on semi-interpenetrating polymer network (semi-IPN) structures of Nafion , polyimidazole (PI) [196-198], polybenzimidazole (PBI) [199], and poly(vinyIidene fluoride) (PVDF) [200] were reported. As shown in Fig. 2.35, the composite membranes with... 

Poiyphosphazene Biends Blends of sulfonated polyphosphazene, for example, sulfonated poly[bis(3-methylphenoxy)phosphazene] or poly[(bisphenoxy)phosphazene] (see Fig. 29.14) with either an inert organic polymer such as poly(vinylidene fluoride) (Pintauro and Wycisk, 2004 Wycisk et al., 2002) or polyacrylonitrile (Carter et al., 2002) or a reactive polymer (e.g., polybenzimidazole) (Wycisk et al., 2005) have been investigated. The resultant membranes had conductivities of 0.01-0.06 S/cm (in water at 25°C) and equilibrium water swelling from 20 to 60% (at 25°C). Blends of poly[(bisphe-noxy)phosphazene] and polybenzimidazole (where acid-base complexation occurred between the sulfonic acid and the imidazole nitrogen) exhibited good mechanical properties and low methanol permeability. MEAs with this membrane material outperformed Nafion 117 in a DMFC at 60°C with concentrated (5-10 M) methanol feeds. With 1.0 M methanol and 0.5 L/min ambient air at 60°C, the maximum power density was 97 mW/cm and the methanol crossover was 2.5 times lower than that with Nafion 117 (Wycisk et al., 2005). 

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