Methacrylic acid conductometric titration

The latexes were ion-exchanged with Dowex 50W(H+) resin and the Dowex 50W(H+)-Dowex 1 (0H ) mixed resin in combination with the Dowex 50W(Na" ")-Dowex 1 (0H ) resin, and the ion-exchanged samples were titrated conductometrically. The samples treated were the latex, the aqueous serum, the latex particles separated from the serum, and the latex particles swollen or dissolved in 80 20 dioxane-water mixture. The total oxygen content was determined by neutron activation and the total sulfur content by X-ray fluorescence. Material balances of acrylic or methacrylic acid found in the serum, on the particle surface, and inside the particle agreed with the amount added to within 5-10%. 

Giebeler et al. [73] investigated the polyelectrolyte complex formation of triblock copolyampholytes, polystyrene-frZock-poly( 2 or 4)-vinylpyridine)-b/oc/c-poly(methacrylic acid). By potentiometric, conductometric and turbi-dimetric titrations of acidic THF/water solutions the formation of an interpolymer complex at the isoelectric point was found, in which most likely the hydrophobic polystyrene cores are embedded in a mixed corona of the two polyelectrolyte blocks. 

Using primarily potentiometric and conductometric titration, several investigators also reported variations in the distribution of the carboxylic acid monomer within the AST emulsion particles. Guziak and Maclay (14) showed that carboxylic acid monomers tended to concentrate near the particle surface of the styrene-acrylic and styrene-butadiene latices studied. Acrylic acid had a greater tendency for surface concentration than did methacrylic acid. Treatment of the latices containing greater than about 20% carboxylic acid monomer with inorganic base produced clear aqueous solutions that were extremely viscous. In an electrophoretic study, Matsumoto and Shimada (16) also found a preferential concentration of acrylic acid near the surface of latices. In contrast, methacrylic acid diffused readily into the particles, where it copolymerized favorably with methyl methacrylate. 

Conductometric analysis of some latexes leads to the conclusion that most of the polymerized acid ends up on the surface of the particles while in other systems a majority of the acid is not titratable and is assumed to be buried within the particles. For instance, conductometric titrations of the three latexes described in Figure 12 showed that greater than 90% of the acrylic acid added in the polymerization was associated with the particles and titratable. On the other hand, polystyrene and poly(methyl methacrylate) latexes generally yielded conductometric results showing a considerable fraction of the acid buried (31). Since, at the levels of incorporated acid studied, the PST and PMMA latexes did not expand upon raising the pH, it could be argued that in the acrylic case (Fig. 12) all the acid was detected because the particles expanded to bare previously buried groups. But poly(butyl acrylate) latexes were found to exhibit no expansion when neutralized with base, and conductometric titrations showed that most of the acid added in the polymerization was detected on the particles (39). 

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