Meaning
Quaternary ammonium compounds in organic solvents function as strong, non-aqueous basic titrants for the determination of weak acid groups in polymers. Using tetra-n-butylammonium hydroxide allows for the precise measurement of carboxyl end groups in polyester resins without causing polymer precipitation. It is the preferred reagent for automated potentiometric titrations.
Potentiometric Titration
An automated titrator monitors the change in electrical potential as the base is added to the dissolved polymer solution. The addition of tetra-n-butylammonium hydroxide produces a sharp inflection point that corresponds to the complete neutralization of the carboxyl groups. This high sensitivity is essential for detecting low concentrations of acid groups in virgin polymer grades, allowing moulders to verify raw material stability before starting the run.
Solvent Compatibility
Non-aqueous titrations require a base that remains soluble in the organic solvents used to dissolve the polymer. The bulky butyl chains of tetra-n-butylammonium hydroxide ensure high solubility in mixtures of benzyl alcohol and chloroform. This compatibility prevents the clogging of the burette tip and maintains a stable titrant concentration.
Carbonate Avoidance
Absorption of carbon dioxide from the air forms carbonates that interfere with the titration endpoint. The solution of tetra-n-butylammonium hydroxide must be protected with soda-lime guards to prevent this atmospheric contamination. Frequent standardization ensures that the measured normality remains accurate.
