Ionomer chemistry

We will briefly introduce some important ionomers (see Fig. 1), but for a thorough treatment of ionomer chemistry, see, e.g., Refs. . The simplest classification of ionomers is semicrystalline vs. amorphous ionomers. The prototypical semicrystalline ionomer is EMAA (Surlyn, DuPont) neutralized with various cations. Also from DuPont, Nafion is a perfluorinated polyethylene with sulfonic acid or sulfonate groups on short side chains. Other commercial ionomers like Aciplex (Asahi Chemical Company), Flemion (Asahi Glass Company), and Neosepta (Tokuyama) are structurally similar to Nafion. For a recent review on Nafion see Mauritz and Moore. ... 

Since ionomers contain ionic clusters, they adhere well to most polar surfaces. They are used for coatings of golf ball covers. Their thermoplasticity permits pressing in conventional molding machines. The addition of foaming agents produces flexible foams used in shoe soles and weatherstripping. Reviews of ionomer chemistry have appeared... 

PEM research is a multidisciplinary, hierarchical exercise that spans scales from Angstrom to meters. It needs to address challenges related to (i) to ionomer chemistry, (ii) physics of self-organization in ionomer solution, (iii) water sorption equilibria in nanoporous media, (iv) proton transport phenomena in aqueous media and at charged interfaces, (v) percolation effects in random heterogeneous media, and (vi) engineering optimization of coupled water and proton fluxes under operation. Figme 1.13 illustrates the three main levels of the hierarchical structure and phenomena in PEMs. 

Elastic properties of Nafion-type PEMs have been discussed in Silberstein (2008) and Jalani and Datta (2005). Data are available only for macroscopic effective elastic moduli. These properties vary significantly with T and RH, ionomer chemistry, and membrane preconditioning. In the model, information is required for the elastic modulus of microscopic polymer fibrils or walls. These values should be significantly larger than macroscopic values, persumably lying in the range of G = 200 to 400 MPa. 

Moffit, M. et al. (1995) Size control of nanoparticles in semiconductor-polymer composites. 2. Control via sizes of spherical ionic microdomains in styrene-based diblock ionomers. Chemistry of Materials, 1,1185-1192. 

Many methods for the conversion of acid copolymers to ionomers have been described by Du Pont (27,28). The chemistry involved is simple when cations such as sodium or potassium are involved, but conditions must be controlled to obtain uniform products. Solutions of sodium hydroxide or methoxide can be fed to the acid copolymer melt, using a high shear device such as a two-roU mill to achieve uniformity. AH volatile by-products are easily removed during the conversion, which is mn at about 150°C. A continuous process has been described, using two extmders, the first designed to plasticate the feed polymer and mix it rapidly with the metal compound, eg, zinc oxide, at 160°C (28). Acetic acid is pumped into the melt to function as an activator. Volatiles are removed in an extraction-extmder which follows the reactor-extmder, and the anhydrous melt emerges through a die-plate as strands which are cut into pellets. 

FIGURE 5.10 (a) Scientific representation of the three-phase structure of a dry ionomer, consisting of cation clusters, lamellae, and disordered regions. (From Cowie, J.M.G., Polymer Chemistry and Physics of Modern Materials, Intertext, London, 1973.)... 

Wilson, A. D. Kent, B. E. (1971). The glass-ionomer cement a new translucent cement for dentistry. Journal of Applied Chemistry and Biotechnology, 21, 313. 

Crisp, S., Lewis, B. G. Wilson, A. D. (1976d). Glass-ionomer cements chemistry of erosion. Journal of Dental Research, 55, 1032-41. 

Crisp, S., Merson, S. A. Wilson, A. D. (1980). Modification of ionomer cements by the addition of simple metal salts. Industrial Engineering Chemistry, Product Research Development, 19, 403-8. 

Wasson, E. A. Nicholson, J. W. (1991). Studies on the setting chemistry of glass-ionomer cements. Clinical Materials, 7, 289-93. 

Changes in electrical conductivity have occasionally been used to study the setting chemistry of AB cements. Conductivity has been particularly used in the study of dental cements, notably the dental silicate (Wilson Kent, 1968), the zinc polycarboxylate (Cook, 1982), the glass-ionomer cement (Cook, 1982) and the ZOE cement (Crisp, Ambersley Wilson, 1980). 

Dolye, M., Lewittes, M. E., Roelofs, M. G. and Perusich, S. A. 2001. Ionic conductivity of nonaqueous solvent-swoUen ionomer membranes based on fluorosulfonate, fluorocarboxylate, and sulfonate fixed ion groups. Journal of Physical Chemistry B 105 9387-9394. 

Koval, G. A., Spontarelli, T., Thoen, P. and Noble, R. D. 1992. Swelling and thickness effects on the separation of styrene and ethylbenzene based on facilitated transport through ionomer membranes. Industrial and Engineering Chemistry Research 31 1116-1122. 

Effect of polarity of the solvent on calculated domain size distributions of ionomer. (Reprinted from K. Malek et al. Journal of Physical Chemistry C 111 (2007) 13627. Copyright 2007, with permission from ACS.)... 

J.W. Nicholson, Chemistry of glass-ionomer cements A review/. Biomaterials 19 (1998) 485-494. 

Shao, RL., Mauritz, K.A., and Moore, R.B., Perfluorosulfonate ionomer/mixed inorganic oxide nanocomposites via polymer-in situ sol-gel chemistry, Chem. Mater, 1, 192, 1995. 

P.L. Shao, K.A. Mauritz, and R.B. Moore. [Perfluorosulfonate ionomer] [Si02-Ti02] nanocomposites via polymer-in situ sol-gel chemistry Sequential alkoxide procedure. Journal of Polymer Science Part B-Polymer Physics 34, 873-882 1996. 

P. Dimitrova, K.A. Eriedrich, B. Vogt, and U. Stimming. Transport properties of ionomer composite membranes for direct methanol fuel cells. Journal of Electroanalytical Chemistry 532, 75-83 2002. 

The studies described in this paper were designed to use the special properties of ionomers, but they are not the only type of chemistry that does so. Other chemical systems that employ ionomer properties include their use as sources of protons of high effective acidity (superacidity) in the catalysis of organic reactions (9-11) and then-use as integral components of chemically active membranes (e.g. cell dividers or electrode coatings) (12). 

The study of chemistry in ionomers will be illustrated in three ways. The first involves several feasibility studies, specifically the reactions of metal ions with simple gaseous molecules. The second involves results of studies of systems of potential catalytic importance. And, the third illustrates the study of particle formation and reaction kinetics. They are illustrative of a body of work in this area (14-18). 

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