Polyelectrolytes, cross-linked

Self-aggregation mycelial pellets, microbial floes, polyelectrolytes, cross-linking agents... 

Polyelectrolyte (cross-linked) Ion-exchange Ion-exchange resins Sulfonated polystyrene aminated polystyrene... 

Marinsky, J. A. 1985. An interpretation of the sensitivity of weakly acidic (basic) polyelectrolyte (cross-linked and linear) eqnilibria to excess neutral salt. The Journal of Physical Chemistry 89, no. 24 5294-5302. doi 10.1021/jl00270a035. 

L. Setiawan, R. Wang, S. Tan, L. Shi, A.G. Fane, Fabrication of poly(amide-imide)-polyethersulfone dual layer hollow fiber membranes applied in forward osmosis by combined polyelectrolyte cross-linking and depositions. Desalination, 312 (2013) 99-106. 

Modification of the membranes affects the properties. Cross-linking improves mechanical properties and chemical resistivity. Fixed-charge membranes are formed by incorporating polyelectrolytes into polymer solution and cross-linking after the membrane is precipitated (6), or by substituting ionic species onto the polymer chain (eg, sulfonation). Polymer grafting alters surface properties (7). Enzymes are added to react with permeable species (8—11) and reduce fouling (12,13). 

Some commercial durable antistatic finishes have been Hsted in Table 3 (98). Early patents suggest that amino resins (qv) can impart both antisHp and antistatic properties to nylon, acryUc, and polyester fabrics. CycHc polyurethanes, water-soluble amine salts cross-linked with styrene, and water-soluble amine salts of sulfonated polystyrene have been claimed to confer durable antistatic protection. Later patents included dibydroxyethyl sulfone [2580-77-0] hydroxyalkylated cellulose or starch, poly(vinyl alcohol) [9002-86-2] cross-linked with dimethylolethylene urea, chlorotria2ine derivatives, and epoxy-based products. Other patents claim the use of various acryUc polymers and copolymers. Essentially, durable antistats are polyelectrolytes, and the majority of usehil products involve variations of cross-linked polyamines containing polyethoxy segments (92,99—101). 

Equations for the evaluation of formation constants of complexed ion species in cross-linked and linear polyelectrolyte systems. J. A. Marinsky, Ion Exch. Solvent Extr., 1973,4, 227-243 (18). 

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. 

The process described is referred to as ion-exclusion as discussed by Asher and Simpson 9. The resins used are normal and the non-ionic molecules are assumed to be small enough to enter the pores. When large non-ionic molecules are involved, an alternative process called ion-retardation may be used, as discussed by Hatch et al. W]. This requires a special resin of an amphoteric type known as a snake cage poly electrolyte. The polyelectrolyte consists of a cross-linked polymer physically entrapping a tangle of linear polymers. For example, an anion exchange resin which is soaked in acrylic acid becomes entrapped when the acrylic acid is polymerised. The intricacy of the interweaving is such that counter-ions cannot be easily displaced by other counter-ions. On the other hand, ionic mobility within the resin maintains the electro-neutrality. The ionic molecule as a... 

By contrast, membranes U-1, A-2 and X-2 are all chlorine sensitive, each responding in a unique manner. U-1 is a thin film composite membrane, the active layer consisting of cross-linked poly(ether/urea) polymer. A-2 is a homogeneous aromatic polyamide containing certain polyelectrolyte groups. X-2 is a thin film composite membrane of proprietary composition. 

Note 1 A polyelectrolyte network is sometimes called a cross-linked polyelectrolyte. Use of the latter term is not recommended unless the polyelectrolyte network is formed by the cross-linking of existing polyelectrolyte macromolecules rather than by nonlinear polymerization. (See the definition of a crosslink, definition 1.59, ref [4].)... 

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]. 

Zinc polycarboxylate, the first polyelectrolyte dental material, was developed and used as early as 1968 [124]. These materials are formed by the reaction of a zinc oxide powder with an aqueous solution of poly(acrylic acid). The zinc ions cross-link the polyacid chains and form a cement. A few years after the development of zinc polycarboxylate cements, Wilson and Kent introduced the first glass-ionomer cement (GIC) [125]. Glass-ionomer cements are formed... 

A synthetic ion-selective (ion-exchange) membrane is a dense, nonporous, mechanically stable polymer film about 0.01 —0.04 cm thick. By nonporosity we mean the absence of pores (possibly very tortuous transmembrane channels) with a typical radius above 5 — KM (10-8 cm). Structurally the membrane material is a cross-linked polyelectrolyte. This latter is a polymer containing chemical groups that while in contact with an aqueous solvent are capable of dissociation into charges which remain fixed to the polymer core and counterions which are free to move in the solution. 

The word cross-linked implies that polymer molecules are chemically bridged by a cross-linking agent. Thus cross-linking provides the polyelectrolyte material with properties of a solid, whereas a noncross-linked concentrated polyelectrolyte solution is mechanically a loose, jelly-like object. 

Amberlite. Trade name for resorcinol type resins used for wood adhesives and manufd by the Rohm Haas Co, Phila 5,Pa. Also a trade-mark name for insoluble crossed-linked polyelectrolytes (ion-exchange resins). Used for water conditioning and other purposes... 

Modification of the membranes affects the properties, Cross-linking improves mechanical properties and chemical resistivity, Fixed-charge membranes are formed by incorporadng polyelectrolytes into polymer solution and cross-linking after the membrane is precipitated, or by... 

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