I'm synthesizing a PLLA grafted with itaconic anhydride in a rheocord mixer. After the grafting, I would like to determine the concentration of the grafted itaconic anhydride.
I dissolved a grafted PLLA sample in THF and then I carried out an acid–base titration with 0.005 M potassium hydroxide (KOH) in ethanol.
I tried to determine the equivalent point in two different ways at 25°C:
1) by means of phenolphtalein as indicator;
2) by means of a pH-meter (CRISON TitroMatic 1S equipped with an electrode CRISON 52.2) measuring the pH and the conductivity.
In both cases I had problems:
1) I can't appreciate the color changing of the indicator;
2) the system seems to be unstable and both the pH and the conductivity fluctuate.
I guess the problem is related with the solvent (THF) because when I tried to perform a similar titration in a water/ethanol solution the pH-meter gave stable results.
My questions are:
Is there any alternative method to determine the anhydride concentration?
Or is there any solution to let my system be more stable to perform a pH measure?
Best regards,
Francesco Chiacchio
acid value (or neutralization number or acid number or acidity) is the mass of potassium hydroxide (KOH) in milligrams that is required to neutralize one gram of chemical substance,] The acid number is a measure of the number of carboxylic acid groups in a chemical compound, such as a fatty acid, or in a mixture of compounds. In a typical procedure, a known amount of sample dissolved in an organic solvent (often isopropanol) and titrated with a solution of potassium hydroxide (KOH) of known concentration using phenolphthalein as a color indicator.
The acid number is used to quantify the acidity of a substance . It is the quantity of base, expressed in milligrams of potassium hydroxide, that is required to neutralize the acidic constituents in 1 g of sample.
Dear Francesco,
You should try to use NMR. Not possible for you?
Stéphane
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