Overview
ISO 4764:2024 - Plastics - Polyols for use in the production of polyurethanes - Determination of degree of unsaturation by using iodine method specifies a laboratory titration method to quantify the degree of unsaturation in polyether polyols used for polyurethanes. The method uses the Wijs reagent (iodine monochloride, ICl) in glacial acetic acid as the addition reagent, followed by liberation of iodine with KI and titration with sodium thiosulfate. It is not applicable to unsaturations conjugated with carbonyl, carboxyl or nitrile groups.
Key topics and requirements
- Principle: Addition of ICl (Wijs reagent) to carbon–carbon double bonds; liberated iodine is titrated with standardized 0.1 N sodium thiosulfate using starch as an indicator. The degree of unsaturation is calculated from blank-corrected titration volumes.
- Reagents and solvents: Preparation and storage of Wijs reagent; examples of analytical solvents (methanol, ethanol, propanols, cyclohexane, chloroform). Use of KI solution and starch indicator is required.
- Apparatus: Standard laboratory glassware and volumetric/gravimetric equipment per referenced ISO laboratory glassware standards.
- Procedure: Dissolve sample in solvent, add Wijs reagent, incubate in the dark (1 h), add KI, then titrate liberated iodine with sodium thiosulfate. Use blank titration and apply calculation U = (B − V) × F / (2 S) to express unsaturation in meq/g (as given in the standard).
- Correction for additives: If antioxidants or other additives with unsaturated bonds are present (e.g., BHT), measure the additive separately and apply the correction formulas provided.
- Limitations: Not suitable for conjugated unsaturated systems; precision and bias data were not available at publication.
Applications and who uses it
- Quality control and incoming inspection for polyurethane polyols manufacturers and converters.
- R&D and polymer chemistry laboratories monitoring unsaturation levels that affect curing, crosslinking and final polymer properties.
- Contract testing and certification labs performing comparative analysis or replacing mercury-based methods.
- Environmental and safety-conscious labs transitioning from mercuric acetate titration (ISO 17710) to a non-mercury alternative.
Related standards
Keywords: ISO 4764:2024, degree of unsaturation, polyols, polyurethanes, iodine method, Wijs reagent, iodine monochloride, ICl, titration, sodium thiosulfate, additive correction.