Partial Acid Value of Unsaturated Polyester Resin as per DIN EN ISO 2114

The quantity of potassium hydroxide needed for neutralization of half of the anhydride groups, all free acids and all carboxyl-terminated groups of an unsaturated polyester resin (UPR), is indicated by the partial acid value (also referred to as “partial acid number”).

Determination of the partial acid number using automated potentiometric titration in accordance with DIN EN ISO 2114 is explained in this application note. This technique employs KOH in ethanol as the titrant.


Unsaturated polyester resin (UPR)

Sample Preparation

Sample preparation is not required.



A blank is determined without UPR, using the same methodology as the sample.


Approximately 3 grams of UPR sample is weighed using the balance and transferred to the titration vessel. Using automated programme, 25 mL of acetone and 50 mL of solvent mixture are added to the UPR sample in the titration vessel.

The mixture is allowed to react for 2 minutes, after which the titration is carried out using KOH in ethanol with 0.1 mol/L concentration. The process is continued until after the equivalence point is reached.


. .
907 Titrando 2.907.0010
800 Dosino, 3x 2.800.0010
814 USB Sample Processor (2T/0P) 2.814.0130
Dosing unit 50 mL, 2x (solvent mixture, acetone) 6.3032.250
Dosing unit 20 mL, (titrant) 6.3032.220
741 Magnetic stirrer, 2x 2.741.0010
843 Pump station (peristaltic) 2.843.0150
Sample rack, PP, 22 x 120 mL 6.2041.470
Titration head, 3x NS 14 6.1458.040
Sample beaker, PP, 22 x 120 mL 6.1459.300
Titration head with DIS-Cover 6.9914.158
DIS-Cover lids for 120 mL PP beakers 6.9914.164
Solvotrode easyClean, LiCl sat. in EtOH 6.0229.020
tiamo™ 2.5 6.6056.252


. .
Titrant c(KOH) = 0.1 mol/L in ethanol, if possible this solution should be bought from a supplier.
Solvent mixture Toluene / ethanol, Φ (toluene) = 66.6% (v/v)


. .
Mode DET U
Pause 30 seconds
Signal drift 20 mV/min
Stirrer speed 8
Max. waiting time 38 seconds
Meas. point density 4
Min. increment 50 µL
Max. increment Off
EP criterion 5
EP recognition all


. .
Partial acid number / (n = 5) s(rel)
19.93 mg KOH / g 0.1%

This information has been sourced, reviewed and adapted from materials provided by Metrohm AG.

For more information on this source, please visit Metrohm AG.


Please use one of the following formats to cite this article in your essay, paper or report:

  • APA

    Metrohm USA Inc.. (2020, May 18). Partial Acid Value of Unsaturated Polyester Resin as per DIN EN ISO 2114. AZoM. Retrieved on May 28, 2024 from

  • MLA

    Metrohm USA Inc.. "Partial Acid Value of Unsaturated Polyester Resin as per DIN EN ISO 2114". AZoM. 28 May 2024. <>.

  • Chicago

    Metrohm USA Inc.. "Partial Acid Value of Unsaturated Polyester Resin as per DIN EN ISO 2114". AZoM. (accessed May 28, 2024).

  • Harvard

    Metrohm USA Inc.. 2020. Partial Acid Value of Unsaturated Polyester Resin as per DIN EN ISO 2114. AZoM, viewed 28 May 2024,


  1. Milind Parab Milind Parab India says:

    Dear Sir,
    Could this process of ascertaining Partial Acid Value, be incorporated during the UPR manufacturing process?
    At the moment we are unable to control the acid value accurately; presently each time we have to sample the UPR for acid value, manually. Please suggest a process we could employ as a part of the manufacturing process to check the acid value.
    Thank you.

The opinions expressed here are the views of the writer and do not necessarily reflect the views and opinions of

Ask A Question

Do you have a question you'd like to ask regarding this article?

Leave your feedback
Your comment type

While we only use edited and approved content for Azthena answers, it may on occasions provide incorrect responses. Please confirm any data provided with the related suppliers or authors. We do not provide medical advice, if you search for medical information you must always consult a medical professional before acting on any information provided.

Your questions, but not your email details will be shared with OpenAI and retained for 30 days in accordance with their privacy principles.

Please do not ask questions that use sensitive or confidential information.

Read the full Terms & Conditions.