Cross-linking ionic

The best heat resistance is obtained when nickel dibutyldithiocarbamate [13927-77-0] (NBC) is incorporated into the compound. NBC contributes to the heat resistance by causing the elimination of unused sulfonyl chloride groups which are then unavailable for additional cross-linking during heat aging. The presence of large amounts of Htharge probably also result in some ionic cross-link formation. 

It may also be argued that plasticised PVC may be considered as a thermoplastic elastomer, with the polymer being fugitively cross-linked by hydrogen bonding via the plasticiser molecules. These materials were, however, dealt with extensively in Chapter 12 and will not be considered further here. The ionomers are also sometimes considered as thermoplastic elastomers but the commercial materials are considered in this book as thermoplastics. It should, however, be kept in mind that ionic cross-linking can, and has, been used to fugitively crosslink elastomeric materials. 

In solutions, the counterions of poly electrolytes are HjO (for the polyacids) and OH (for the polybases), cations such as K+ and Na, or anions such as Cl (for the polysalts). The addition of polyvalent counterions (such as Ca, Mg, Cu, AT ) produces ionic cross-linking interfering with solubility The polyelectrolyte precipitates and may be redissolved upon addition of a strong acid (such as HCl). This can be regarded as a special case of ion exchange. 

Jahangir, L. M. and Samuelson, O., Cation-exchange resins and non-ionic cross-linked polymers in analysis of aqueous solutions for organic contaminants, Anal. Chim. Acta, 100, 53, 1978. 

Ionic cross-linking can be achieved in a number of systems and different microstructures result. For rigid chains it is possible for the ion to coordinate in a specific manner with the chain. Alginates are a good example of this. These are natural polymers derived from a brown macro-algae. The method of extraction and the species of the algae influences the chemistry and hence the rheology of these polymers. There... 

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.)...

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).

The properties exhibited by polyelectrolytes make them nearly-ideal candidates for dental material formulations. Dental polyelectrolytes are generally considered to be nontoxic and are able to adsorb chemically to the hydrophilic surface of tooth material through ionic interactions. Ionic cross-linking of the polyelectrolyte with multivalent cations (Zn2+, Mg2+, Al3+, Ca2+) results in the formation of a rigid and insoluble cement matrix. The stability and strength of the cement is attributed to the fact that, if a bond is broken, it can be reformed as long as the other bonds are maintained. Even today, polyelectrolytes are the only materials which are known with certainty to form a bond, which is stable with time, to tooth material [120]. In addition to long-term stability, many polyelectrolytes are translucent and possess cariostatic properties [121]. 

C Elastomer phase reported to be ionically cross-linked (52). 

There is also a fairly large market for high cis BR in solid core golf balls. In this application, the polymer is compounded with zinc acrylate and the mixture is cured with peroxide.47 This produces an ionically cross-linked compound that has outstanding resilience. The covers are also ionomers with superior cut resistance. In the last few years the golf ball market has been shifting away from the traditional wound ball to these new solid core balls that use polybutadiene. 

Pastes inpregnated with PMMA or sulphur are still sufficiently permeable to water that expansion occurs on long exposure (F46). In polymer-impregnated (S108) and MDF (R64) cement pastes, there is evidence of interaction between Ca ions and carboxylate and possibly other groups of the polymer. In MDF pastes made with calcium aluminate cement, the polymer (PVA) was found to inhibit the normal hydration reactions of the cement, but to react with Ca and AH to give an ionically cross-linked polymer and calcium acetate. TEM showed the material to be essentially a dispersion of grains of clinker or hydration products in a continuous polymer matrix. 

According to literary data, the following mixtures of aromatic/aliphatic-aromatic hydrocarbons were separated toluene/ n-hexane, toluene/n-heptane, toluene/n-octane, toluene/f-octane, benzene/w-hexane, benzene/w-heptane, benzene/toluene, and styrene/ethylbenzene [10,82,83,109-129]. As membrane media, various polymers were used polyetherurethane, poly-esterurethane, polyetherimide, sulfonyl-containing polyimide, ionicaUy cross-linked copolymers of methyl, ethyl, n-butyl acrylate with acrilic acid. For example, when a composite polyetherimide-based membrane was used to separate a toluene (50 wt%)/n-octane mixture, the flux Q of 10 kg pm/m h and the separation factor of 70 were achieved [121]. When a composite mebrane based on sulfonyl-containing polyimide was used to separate a toluene (1 wt%)/ -octane mixture, the flux 2 of 1.1 kg pm/m h and the separation factor of 155 were achieved [10]. When a composite membrane based on ionically cross-linked copolymers of methyl, ethyl, w-butyl acrylate with acrilic acid was used to separate toluene (50 wt%)//-octane mixture, the flux Q of 20-1000 kg pm/m h and the separation factor of 2.5-13 were achieved [126,127]. 

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