Blends ionic cross-linking

Figure 20. Electro-osmotic drag coefficients of diverse membranes based on perfluorinated polymers (Dow - and Nafion/silica composites ) and polyarylenes (S—PEK/ PSU blends, ionically cross-linked S—PEK/PBP ), as a function of the solvent (water/methanol) volume fraction Xy (see text for references). Lines represent data for Nafion and S—PEK (given for comparison) for data points, see Figure 15. Dashed lines correspond to the maximum possible electro-osmotic drag coefficients for water and methanol, as indicated (see text).

Blends of sulfonated polymers and polymers containing basic moieties have also been made. Represented schematically in Figure 3.35, ionic cross-linking between acidic and basic sites generally leads to improved mechanical and thermal stabilities. strong interactions within these blends results... 

Schematic representation of ionically cross-linked acid-base blend membranes. (From Kerres, J. A. 2005. Fuel Cells 5 230-247.)...

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). 

Lopattananon et al. (2007) have prepared blends of maleated natural rubber and carboxylated nitrile rubber in the presence of zinc acetate to form a compatibilizing copolymer through ionic cross-links. The effect of different maleation levels was studied. Blend properties were compared to those for blends with unfunctionalized rubbers. 

The first LDPE/HDPE blends were patented by du Pont de Nemours before Z-N polymers became available (Roedel 1961). The blend comprised an experimental HOPE (p = 0.939-1.096 g mL Tm 120 °C) obtained by polymerizing C2 in its own medium at T 0 °C and P 31 MPa, using, e.g., a hydroxy-cyclohexyl-L-hydroperoxide catalyzed by ferrous chloride tetrahydrate. The blend showed 50 % moisture permeabDity of that by LDPE. In 1958 Phillips Petroleum patented PE/PE blends, either cross-linked in electron accelerator or not (Canterino and Martinovich 1963 Nelson 1964). Mitsubishi disclosed PO blends comprising vinyl-trimethoxysUane-grafted polyolefin (PP, LDPE, EPR, or EVAc) and ethylene-acryloyloxy tetramethylpiperidine copolymer. These water-cross-linkable resins were used for the manufacture of weather-resistant cross-linked PO pipes in outdoor applications (Ohnishi and Fukuda 1993). Thermally reversible cross-links (based on ionic interaction between maleated- and glycidyl methacrylate-grafted polyolefins) were also proposed (Okada 1994 Okada and Masuyama 1994). 

Polymers of linear or network structure with ionic groups which by addition of the appropriate counterions can be ionically cross-linked. A copolymer of ethylene and acrylic acid is used as a compatibilizer in polyamide blends. Converted to ethylene-zinc acrylate copolymer, Surlyn M jg y gd as packaging film. Other ionic polymers are applied as polyelectrolytes, ion exchange resin, etc. 

SI in the following, see Fig. 4.5) [43]. Blend compositions (in wt%) from 100 Bl/0 SI up to 50/50 were investigated. It was noted that the acid doping level decreased with decreasing PBI content which can be traced back to both the ionical cross-links by interactions of with Bl and by decreasing Bl proportion in the blend for the 50/50 blend, a maximum ADL of 8.5 with respect to the PBI component was reached, while the pure Bl maximal ADL was 16. The ionic conductivity of the blend membranes was measured in dependence of temperature, acid... 

It was found that the doped blend membranes exhibited higher conductivities (in excess of 0.1 S cm ) than pure M when applying equal doping conditions. The blend membranes showed strongly improved tensile strength, compared to pure M which can be explained by the ionical cross-links within the membrane. 

It is clearly seen from the characterization results that (1) the chemical stability of the polystyrene sulfonic acid blends is in the blend much higher than in the pine polymers due to acid-base cross-linking, (2) the radical stability of the blend membranes is higher than that of pure B4 which is again due to the ionical cross-linking, and (3) the radical stability of the S4b blend membrane is much better compared to that of the S4b blend membrane. The better radical stability of the B4S4b blend can also be seen... 

The preparation (Fig. 4.1) and structure (Fig. 4.3) of an HsPOa-doped ionically cross-linked acid-base blend membrane (membranes 1927A and 1940 in Table 4.7) was already depicted schematically in the introduction. Figure 4.11 presents the preparation and the structure of a covalently cross-linked blend membrane (membranes 1921C, 1925C, and 1938), and Fig. 4.12 the preparation and structure of a covalent-ionically cross-linked blend membrane (membrane 1943). 

Fig. 4.12 Preparation and structure of covalent-ionically cross-linked intermediate-T blend membranes...

In Fig. 4.23, the TGA traces of the ionically cross-linked membrane 1927A (sulfonated crosslinker) are presented, and in Fig. 4.24 those of 1940 (phosphonated cross-linker), indicating the excellent chemical stabilities of these two blend membranes. 

Continuation of the R D work on covalent-ionically cross-linked blend membranes, where the different blend components PBI/acidic polymer/bromomethylated polymer are optimally matched to one another to yield intermediate-T fuel cell membranes with a property profile tailored to the respective membrane application such as fuel cells or electrolysis, respectively... 

It is not out of place to give brief mention to the ionomers introduced by Du Pont in the mid-1960s. To produce these polymers an alkene, usually ethylene, is copolymerized with a few per cent of a second monomer such as an -carboxylic acid in order to introduce a few carboxylic acid groups into the chain. The copolymer is then blended with a metal salt which ionizes the acid group. Heat fugitive ionic cross-links form (between carboxylic groups via the metal... 

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... 

Covalent-Ionically Cross-Linked (Blend) Membranes... 

Both ionically cross-linked membranes (splitting-off of the ionic bonds at T = 70-90°C) and covalently cross-linked membranes (bleeding-out of sulfonated macromolecules from covalently cross-linked blend membranes, brittleness of dry membranes) show disadvantages. To overcome these disadvantages, we started the development of covalent-ionically cross-linked membranes [60] ... 

Covalently or ionically cross-linked blend membranes, filled with p-sized oxide (SiOj, TiOj) or layered zirconium phosphate ZrP, introduced as a powder into the polymer solution. The problem of this membrane type is that inorganic oxide or salt powders tend toward agglomeration in the polymer solution and, after solvent evaporation, in the membrane, which reduces the active surface for water adsorption and possible proton transport dramatically. Therefore, we applied... 

Covalently or ionically cross-linked blend membranes, filled with layered ZrP by ion-exchange precipitation ... 

Comparison of the morphology of binary and ternary covalent-ionically cross-linked membranes As mentioned, the ternary covalent-ionically cross-linked blend membranes show phase separation, due to incompatibility of the sulfinate and the basic blend component. This problem was overcome by preparation of binary covalent-ionically cross-linked blend membranes The polysulfonate was mixed with a polymer carrying both sulfinate and basic groups in statistical distribution onto the same backbone. The TEM micrographs of the binary blend membrane clearly showed a homogeneous morphology of this membrane [80]. 

Comparison of the properties of binary and ternary covalent-ionically cross-linked membranes. The properties of a ternary covalent-ionically cross-linked blend membrane (ICVT-1028) were compared with the properties of a binary covalent-ionically cross-linked blend membrane (ICVT-WZ-054), both membranes showing comparable lEC and proton conductivity [79,80], The main difference in properties between the two membranes was their different swelling... 

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