Investigation of the particle surface of anionic polyurethane dispersions with COO−‐groups

Polyurethanes, containing both terminal and nonterminal COOH ‐ groups, were synthesized from poly(propylene oxide), 1,2,4‐benzenetricarboxylic acid anhydride and 1,6‐hexamethylene diisocyanate. Aqueous dispersions were prepared from the acetonic solutions after partial neutralization. The concentration of carboxylic groups present before the formation of the dispersion was determined quantitatively by potentiometric titration with methanolic KOH in nonaqueous solution. The determination of the titratable COOH‐ and COO−‐groups after dispersion formation was carried out by conductometric or potentiometric titration with NaOH or HCl. It was found, that all COOH‐ and COO−‐groups present in the system could be detected in the dispersion. This indicates that neither ion‐pairs nor COOH‐groups are locked inside of the latex particles. In addition to latex particles water‐soluble electrolytes with a relatively high ion concentration are formed during synthesis. Thereby, the formation of imbedded ion‐pairs is reduced or even prevented.