Polymers charged species

AB cements are not only formulated from relatively small ions with well defined hydration numbers. They may also be prepared from macromolecules which dissolve in water to give multiply charged species known as polyelectrolytes. Cements which fall into this category are the zinc polycarboxylates and the glass-ionomers, the polyelectrolytes being poly(acrylic acid) or acrylic add copolymers. The interaction of such polymers is a complicated topic, and one which is of wide importance to a number of scientific disciplines. Molyneux (1975) has highlighted the fact that these substances form the focal point of three complex and contentious territories of sdence , namely aqueous systems, ionic systems and polymeric systems. 

Here the first term is the usual diffusive current, with Dc being the usual cooperative diffusion constant of the polymer molecule. The second term is a convective current due to the presence of induced electric field arising from all charged species in the system, p is the electrophoretic mobility of the polymer molecule derived in the preceding section. From the Poisson equation, we obtain... 

Water solubility is determined by polymer structure (linear, branched, etc.), concentration and placement of charged species [ionomeric (cationic or anionic) or amphoteric (cationic and anioiuc)], hydrophihc/hydrophobic substituents, and hydrogen bonding, to name the more commonly encountered factors. In general, polymer water solubility requires polar functional... 

In general, the adsorption of a surfactant on particles with previously adsorbed polymer can be influenced by (i) a reduction of surface area available for adsorption as a result of the presence of adsorbed polymer, (ii) possible interactions between polymer and surfactant in the bulk solution or in the interfacial region (that is, surfactant with loops, tails or trains of adsorbed polymer molecules), (iii) the steric effect of adsorbed polymer, preventing approach of surfactant molecules for adsorption at the surface, or (iv) possible electrostatic effects if polymer and/or surfactant are charged species. 

Charge on a polymer molecule can also affect reactivity by altering the concentration of the small molecule reactant within the polymer domains. The reaction of a charged polymer with a charged reactant results in acceleration for oppositely charged species and retardation when the charges are the same. For example, the rate constant for the KOH saponification of poly(methyl methacrylate) decreases by about an order of magnitude as the reaction proceeds [Plate, 1976]. Partially reacted poly(methyl methacrylate) (IV) repells hydroxide ion, while... 

The presence of highly electronegative atoms which can participate in hydrogen bonding is required for the solubility of polymers in water. Such groups include amines, imines, ethers, alcohols, sulfates, carboxylic acids and associated salts, and, to a lesser extent, thiols. The water solubility is also affected by pH and the formation of charged species. Thus the copolymer derived from vinylamine and vinyl sulfonate is not soluble in water, whereas the corresponding sodium salt of this copolymer is water-soluble. 

This reaction profile of the polymer complex has some similarities with the phenomenon of the polyelectrolyte-catalyzed reactions. It has been reported that the reactions between two positively charged species in aqueous solution are drastically accelerated in the presence of polyanionsS2 84 For example, the electron-transfer reaction between [Co(IIIXen)2(Py)Cl]2+ and [Fe(IIXOH2)6]2+ is very slow because the reaction occurs between two cations however, the addition of a small amount of poly(styrenesulfonate) accelerates the reaction by a factor of 103 84). This result is also interpreted as indicating that the two positively charged reactants are both concentrated in the polyanion domain, so that they encounter each other more frequently [Fig. 17(b)]. 

This scheme requires the assumption of extremely strong association of all lithium-oiganics down to at least 10-4 molar concentration if the observed reaction orders are to be obeyed. It assumes in agreement with earlier workers that only unassociated lithium alkyls and aryls are reactive. The six-fold association of butyllithium required is in agreement with physical measurements although admittedly these were carried out at much higher concentrations. Morton and co-workers (69) have shown that the polymer molecules are indeed associated into dimers in this system from a quantitative study of the decrease in solution viscosity on removal of the charged species at the ends of the polymer molecules. 

Figure 1. Examples of conducting polymers and species responsible for charge storage. Top, poly(acetylene) and soliton 2nd, poly-p-phenylene and bipolaron 3rd, poly- -phenylene sulfide 4th, poly(heterocycles) and bipolaron. Bipolarons in poly(furan) have not yet been established.

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