Ionomer behavior

Intermediate cases (between pure polyelectrolyte and pure ionomer behavior) can be realized as well. For these cases 1 (e / fl feT), and some part of counterions is free, while the other forms ion pairs. The ion pairs can essentially influence the behavior of the polymer gel, and this factor has to be taken into account in many situations. ... 

Although ionomer gels are not so widely studied as their polyelectrolyte counterparts, many manifestations of the ionomer behavior were already revealed including supercollapsed state, collapse induced by ionization, and multiplet nanostmctures. 

Olga E. Philippova s main research interests are polyelearolyte and ionomer behavior of polymer gels, linear and cross-linked polyelectrolytes with associating hydrophobic groups, polymer gel/surfactant interactions, interpolymer complexes, and polymer gels with entrapp l linear stiff-chain macromolecules. 

Khokhlov, A.R. and Kramarenko, E.Y., 1994. Polyelectrolyte/ionomer behavior in polymer gel collapse, Macromol. Theory Simul, 3,45-59. 

For almost ten years the properties of ionomer solutions have been studied and lightly sulfonated polystyrene (S-PS) was chosen as the model compound. The properties of S-PS ionomer solutions in polar and nonpolar solvents, which are briefly reviewed, were associated with polyelectrolyte and ionomer behavior respectively. In both cases, structural models have been proposed to explain the rheological and scattering data. A similar study on perfluorinated ionomer solutions is then presented and compared in order to define some general ionomer behavior. 

Several groups " have studied the response of (ethylene/carboxylic acid) copolymers to an applied stress or strain. This type of measurement has been the principle method for determining the unusual features of ionomer behavior. The results of such studies provide clear evidence for the presence of ionic clusters. 

EPDM-Derived Ionomers. Another type of ionomer containing sulfonate, as opposed to carboxyl anions, has been obtained by sulfonating ethylene—propjlene—diene (EPDM) mbbers (59,60). Due to the strength of the cross-link, these polymers are not inherently melt-processible, but the addition of other metal salts such as zinc stearate introduces thermoplastic behavior (61,62). These interesting polymers are classified as thermoplastic elastomers (see ELASTOLffiRS,SYNTHETIC-THERMOPLASTICELASTOLffiRS). 

Telechelic Ionomers. Low molecular weight polymers terminated by acid groups have been treated with metal bases to give ionomers in which the cations can be considered as connecting links in the backbones (67—71). The viscoelastic behavior of concentrated solutions has been linked to the neutralizing cation. 

The combined effects of a divalent Ca counterion and thermal treatment can be seen from studies of PMMA-based ionomers [16]. In thin films of Ca-salts of this ionomer cast from methylene chloride, and having an ion content of only 0.8 mol%, the only observed deformation was a series of long, localized crazes, similar to those seen in the PMMA homopolymer. When the ionomer samples were subject to an additional heat treatment (8 h at 100°C), the induced crazes were shorter in length and shear deformation zones were present. This behavior implies that the heat treatment enhanced the formation of ionic aggregates and increased the entanglement strand density. The deformation pattern attained is rather similar to that of Na salts having an ion content of about 6 mol% hence, substitution of divalent Ca for monovalent Na permits comparable deformation modes, including some shear, to be obtained at much lower ion contents. 

In the preparation and processing of ionomers, plasticizers may be added to reduce viscosity at elevated temperatures and to permit easier processing. These plasticizers have an effect, as well, on the mechanical properties, both in the rubbery state and in the glassy state these effects depend on the composition of the ionomer, the polar or nonpolar nature of the plasticizer and on the concentration. Many studies have been carried out on plasticized ionomers and on the influence of plasticizer on viscoelastic and relaxation behavior and a review of this subject has been given 119]. However, there is still relatively little information on effects of plasticizer type and concentration on specific mechanical properties of ionomers in the glassy state or solid state. 

Aside from ion content, a wide range of properties is available in ionomers by control of various processing variables, such as degree of conversion (neutralization), type of counterion, plasticizer content and thermal treatment. Various examples illustrating possible effects of these variables on mechanical relaxation behavior and on such mechanical properties as stiffness, strength, and time- or energy-to-fracture have been given. 

This process is highly suitable for rubbers with poor solubility. In this process, the rubber sheet is soaked in TEOS or quite often in TEOS-solvent mixture and the in situ sUica generation is conducted by either acid or base catalysis. The sol-gel reaction is normally carried out at room temperature. Kohjiya et al. [29-31] have reported various nonpolar mbber-silica hybrid nanocomposites based on this technique. The network density of the rubber influences the swelling behavior and hence controls the silica formation. It is very likely that there has been a graded silica concentration from surface to the bulk due to limited swelling of the rubber. This process has been predominantly used to prepare ionomer-inorganic hybrids by Siuzdak et al. [48-50]. 

Wilson, A. D., Crisp, S. Ferner, A. J. (1976). Reactions in glass ionomer cements IV. Effect of chelating comonomers on setting behavior. Journal of Dental Research, 55, 489-95. 

The physical properties of the acid- and ion-containing polymers are quite interesting. The storage moduli vs. temperature behavior (Figure 8) was determined by dynamic mechanical thermal analysis (DMTA) for the PS-PIBMA diblock precursor, the polystyrene diblock ionomer and the poly(styrene)-b-poly(isobutyl methacrylate-co-methacrylic acid) diblock. The last two samples were obtained by the KC>2 hydrolysis approach. It is important to note that these three curves are offset for clarity, i.e. the modulus of the precursor is not necessarily higher than the ionomer. In particular, one should note the same Tg of the polystyrene block before and after ionomer formation, and the extension of the rubbery plateau past 200°C. In contrast, flow occurred in... 

The simple water charmel models can explain the ionomer peak and the small-angle upturn in the scattering data of fhe unoriented samples as well as of the oriented films. Interestingly, the helical structure of backbone segments is responsible for fhe sfabilify of fhe long cylindrical charmels. The self-diffusion behavior of wafer and protons in Nation is well described by the water channel model. The existence of parallel wide channels af high wafer uptake favors large hydrodynamic confributions to electro-osmotic water transport and hydraulic permeation. 

Mesoscale calculations, discussed for the membrane in Section 6.5.3, provide insights into segregation behavior, structural correlations, and d5mamical behavior of different phases in CLs. They contribute to furnishing relations among structure, transport properties, and reactivity. Compared to hydrated ionomer membranes (Section 6.5), structural complexity is more pronounced in CLs. 

The electric properties of polymers are also related to their mechanical behavior. The dielectric constant and dielectric loss factor are analogous to the elastic compliance and mechanical loss factor. Electric resistivity is analogous to viscosity. Polar polymers, such as ionomers, possess permanent dipole moments. These polar materials are capable of storing... 

In view of the similarity in behavior of the networks in the ionomer and low density resin, we are able to deduce from modulus and elongation at rupture measurements the relative crosslinking rates. It appears that Surlyn A crosslinks 50 to 60% more rapidly than DFD 6040. The increased crosslinking in the ionomer may be associated with the radio-... 

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