Ionic carboxyl groups

These cements set in 3-5 to 56 minutes (at 37 °C). Infrared spectroscopy showed that as the cement set there was loss of acid carbonyl groups and OH groups associated with calcium hydroxide, and simultaneously formation of ionic carboxylate groups and hydrogen-bonded OH groups. 

The first phase of this study involved measurement of the degree of hydrolysis via conversion of ionic carboxylate groups on the polymer molecule to carboxylic acid groups followed by titration of the acid groups. TP hydrolysis of aqueous vs. saline solutions of PAM, as determined by this route. Is shown in Figure 1. In agreement with other studies (8-10), it is seen that substantial hydrolysis occurs in the absence of base catalyst, but at a slower rate than when a catalyst is present (2,7). 

In water solution, the stearate ions associate into micelles in which the hydrocarbon ends point inward toward one another and away from the water, and ionic carboxyl groups are on the outside of the micelle facing the water (Figure 12.29). 

Ethylene—Dicarboxylic Acid Copolymers. Partial neutralization of copolymers containing carboxyls in pairs on adjacent carbons, eg, ethylene—maleic acid, has been described (11). Surprisingly, there is no increase in stiffness related to neutralization. Salts with divalent metal cations are not melt processible. The close spacing of the paired carboxyl groups has resulted in ionic cluster morphology which is distinct from that of the commercial ionomer family. 

Gross-Linking. A variety of PE resins, after their synthesis, can be modified by cross-linking with peroxides, hydrolysis of silane-grafted polymers, ionic bonding of chain carboxyl groups (ionomers), chlorination, graft copolymerization, hydrolysis of vinyl acetate copolymers, and other reactions. 

Maleic acid and fumaric acid can also be, and are often, incorporated in alkyd resins in the form of the Diels-Alder adduct of rosin. The adducts are tribasic acids which provide pendent carboxyl groups in the resin molecules, which can be saponified to give ionic, and, in turn, water-soluble characteristics to the resin. However, the resultant alkyds often have poorer color retention, toughness, gloss retention, and exterior durabiUty. 

During the 1990s concern increased about the odour and volatility of amino catalysts, particularly in enclosed spaces such as automobiles. Odourless low volatility (and hence low-fogging) catalysts based on salt-like or ionic carboxylates containing active amine centres became available. Another approach was to incorporate amine groups into the polymer to provide a built-in rather than a free-standing catalyst. 

The AH unit was assigned to the carboxyl group, as the sweet taste of compounds 2 and 3 in Table XXIVa is lost when the carboxyl group is absent or when it is converted into the methyl ester (compound 4 in Table XXIVa). It was suggested " that this group mainly interacts with its counterpart on the receptor by ionic interaction. The absence of sweet taste... 

The polyelectrolyte properties of pectins are breefly exposed specially the role of the carboxylic groups distribution along the chain is demonstrated to controll the electrostatic properties. The viscometric behaviour depends on the ionic concentration and on the nature of the counterions in relation with electrostatic repulsions. 

Broadly speaking, in the study of AB cements derived from poly-carboxylic acids, the band of interest falls in the region 1550-1620 cm (Mehrota Bohra, 1983 Bellamy, 1975). This band is the asymmetric stretch of the carboxylate group and its exact position depends on both the nature of the bonding involved (i.e. whether purely ionic or partially covalent), and the nature of any chelation by the carboxylate group (Bellamy, 1975). 

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