Ionomer formation

Sulfonation is very useful chemical modification of polymer, as it induces high polarity in the polymer changing its chemical as well as physical properties. Sulfonated polymers are also important precursors for ionomer formation [75]. There are reports of sulfonation of ethylene-propylene diene terpolymer (EPDM) [76, 77], polyarylene-ether-sulfone [78], polyaromatic ether ketone [79], polyether ether ketone (PEEK) [80], styrene-ethylene-butylene-styrene block copolymer, (SEBS) [81]. Poly [bis(3-methyl phenoxy) phosphozene] [82], Sulfonated polymers show a distinct peak at 1176 cm 1 due to stretching vibration of 0=S=0 in the -S03H group. Another peak appears at 881 cm 1 due to stretching vibration of S-OH bond. However, the position of different vibrational bands due to sulfonation depends on the nature of the cations as well as types of solvents [75, 76]. 

Ionomers are polymers which contain up to about 10% mole percent of ionic group [83-85]. Ionomers show interesting properties because of the presence of different interactions which include hydrogen bonding, formation of charge transfer complexes and ion-ion interactions. Polymers with carboxylic or sulfonic acid groups in its backbone on neutralisation with zinc, sodium or other metal salts form ionic aggregates. 

IR spectroscopy can be used to characterise the formation of ionomers by studying the environment of the anions [85, 86]. Risen and co-workers [87, 88] used far-IR spectra (150 to 400 cm 1) to demonstrate the sensitivity of low frequency vibrations to the anions and cations and the degree of cluster formation in ionomers. For example, styrene sulfonic acid ionomers with Na+ cation shows absorption bands at 220 cm 1, whereas the Cs+ cation shows bands at 100 cm 1. 

The absence of peaks at 1750-1700 cm1 indicates complete ionisation. The nature of band depends on the types of cations. The salts of potassium, caesium and zinc exhibit sharp single bands whereas sodium, calcium, strontium and barium salts show distinct doublet bands [90]. It is due to different ionic environment with various cations. 

Sulfonated ionomers are also characterised by IR spectroscopy [75-77]. Agarwal and coworkers [76] analysed the Zn+2 salt of sulfonated EPDM. The peak at about 1200 cm 1 is due to the asymmetric stretching of the sulfonate group. The band at 1020 cm 1 is ascribed to the symmetric stretching of the -S03 group. The position and nature of the absorption band depend on the nature of the cation [76]. The band at 610-615 cm 1 is due to C-S stretching of the polymer -S03 band. 

---

The most common use of curing agents is with carboxylic latices. Isocyanates and melamines can be used but zinc oxide is the most common curing agent. Zinc oxide cross-links carboxylated latices and improves bond strength by ionomer formation [78]. Carboxylated polychloroprene reacts slowly with zinc oxide in dispersed form, causing a gradual increase in adhesive gel content. This can lead to restricted adhesive shelf life. Resin acid sites compete with the polymer acid sites for Zn(II). The more resin acid sites, the more stable the adhesive. 

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... 

Ionomer formation 150 to 400 Depending on cations in sulfonated ionomers [83-85] [87-90]... 

Conventional SMC is prepared from unsaturated polyester resin and styrene, together with magnesium or calcium oxides or hydroxides. The bases serve to thicken the styrene-polyester solution, probably through ionomer formation.Usually, SMC is used together with fillers such as calcium carbonate and glass fiber reinforcement for high modulus. 

Gelation in polymers may be brought about in several ways temperature changes, particularly important in protein gelation formation polymerization with cross-links phase separation in block copolymers ionomer formation or even crystallization. Such materials are usually thermoreversible for physical cross-links, or thermoset through the advent of chemical cross-Unks. Of course, there must be at least two cross-link sites per chain to induce gelation. A major... 

Water-borne polyurethane coatings are formulated by incorporating ionic groups into the polymer backbone. These ionomers are dispersed in water through neutrali2ation. The experimental 1,12-dodecane diisocyanate (C12DI Du Pont) is especially well suited for the formation of water-borne polyurethanes because of its hydrophobicity (39). Cationomers are formed from IPDI, /V-methyIdiethan olamine, and poly(tetramethylene adipate diol)... 

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. 

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]. 

Water is also a component of set AB cements. In glass-ionomer cements, for example, it may serve to coordinate to certain sites around the metal ions. It also hydrates the siliceous hydrogel that is formed from the glass after add attack has liberated the various metal ions (Wilson McLean, 1988). Such reactions continue long after the initial hardening of the cement is complete, and for this reason water must be retained as far as possible during the first hours and days after formation of the cement. If water is lost from the cement and desiccation occurs, these post-hardening... 

Hicks, M. J., Flaitz, C. M. Silverstone, L. M. (1986). Secondary caries formation in vitro around glass ionomer restorations. Quintessence International, 17, 527-32. 

Ellis and Wilson also examined cement formation from aluminosilicate glasses and concentrated solutions of PVPA (Wilson Ellis, 1989 Ellis, 1989 Ellis Wilson, 1990). These cements, like the glass polyalkenoate cements, are a type of glass-ionomer cement. 

In another study, oscillating rheometry was used to examine the effect of adding various simple metal salts to glass-ionomer cements (Crisp, Merson Wilson, 1980). It was found that cement formation for certain glasses which react only slowly with poly(acrylic acid) could be accelerated significantly by certain metal salts, mainly fluorides such as stannous fluoride and zinc fluoride. Some non-reactive glasses could be induced to set by the addition of such compounds. 

What happens upon equilibration with liquid water instead of water vapor According to Equation (6.13), the capillary radius would go to infinity for PVP —> 1. Thus, in terms of external conditions, swelling would be thermodynamically unlimited, corresponding to the formation of an infinitely dilute aqueous solution of ionomer. However, the self-organized polymer is an effectively cross-linked elastic medium. Under liquid-equilibrated conditions, swelling is not controlled by external vapor... 

Calculations in Roudgar et al. focused on the shortest SGs (i.e., CF3SO3H) under conditions of minimal hydration (i.e., with one H2O per SG). The main parameter considered is the nearest neighbor distance of the terminal, fixed C atoms. It was varied from 5 A < dec 12 A, which encompasses the range of side chain separations found in prototypical ionomer membranes. The VASP based on DFT was used. Figure 6.13 displays the formation... 

Ionomer in Catalyst Layers Structure Formation and Performance... 

Microstructures of CLs vary depending on applicable solvenf, particle sizes of primary carbon powders, ionomer cluster size, temperafure, wetting properties of carbon materials, and composition of the CL ink. These factors determine the complex interactions between Pt/carbon particles, ionomer molecules, and solvent molecules, which control the catalyst layer formation process. The choice of a dispersion medium determines whefher fhe ionomer is to be found in solubilized, colloidal, or precipitated forms. This influences fhe microsfrucfure and fhe pore size disfribution of the CL. i It is vital to understand the conditions under which the ionomer is able to penetrate into primary pores inside agglomerates. Another challenge is to characterize the structure of the ionomer phase in the secondary void spaces between agglomerates and obtain the effective proton conductivity of the layer. 

These coarse-grained MD calculations helped consolidate the main features of microstructure formation in CLs of PEFCs. They showed that the final microstructure depends on carbon particle choices and ionomer-carbon... 

Application of amphiphilic block copolymers for nanoparticle formation has been developed by several research groups. R. Schrock et al. prepared nanoparticles in segregated block copolymers in the sohd state [39] A. Eisenberg et al. used ionomer block copolymers and prepared semiconductor particles (PdS, CdS) [40] M. Moller et al. studied gold colloidals in thin films of block copolymers [41]. M. Antonietti et al. studied noble metal nanoparticle stabilized in block copolymer micelles for the purpose of catalysis [36]. Initial studies were focused on the use of poly(styrene)-folock-poly(4-vinylpyridine) (PS-b-P4VP) copolymers prepared by anionic polymerization and its application for noble metal colloid formation and stabilization in solvents such as toluene, THF or cyclohexane (Fig. 6.4) [42]. 

---