ASTM D4671 Determination of Unsaturation of Polyols

ASTM D4671 Determination of Unsaturation of Polyols

ASTM D4671 includes apparatus and procedure to determine unsaturation of polyether polyols. A potentiometric endpoint determination method is used in this approach. The values are considered as a standard when expressed in SI units.

    Scope:

    ASTM D4671 test method can be used for quality assurance, specification testing, and research. In polypropylene oxides, side reactions that yield unsaturated chemicals produce modest polymers with only one hydroxyl group per chain. Functionality and molecular weight of unsaturated polymers are reduced, while the overall molecular weight distribution is increased. 

    Procedure:

    In ASTM D4671 test method, around 1 g of material is added to a 100-mL titration flask for samples containing 0.033 meq/g or less, then swirled in 2 mL of mercuric acetate reagent solution. The sample prepared is covered with watch glass and it stands for at least 30 min, 50 mL methanol is added first, followed by 0.25 g sodium bromide crystals, and is titrated 0.05 N methanolic KOH to the endpoint. A sample is prepared as directed above, but without the mercuric acetate reagent, the acidity or basicity of the polyol is evaluated for correcting the results. The sample is eventually titrated with 0.05 N methanolic KOH to the potentiometric endpoint. Once the solution has passed the acid endpoint, the operation is repeated and titrated with 0.05 N methanolic HCl.

    Specimen Size:

    For ASTM D4671 test, more than 0.033 milliequivalents (meq) of unsaturated species is used

    Data:

    Given equation is used to determine acidity, meq/g, of given sample:
    VA × N (KOH)/WA = A
    Where:
    VA = volume (mL) of 0.05 N KOH
    N (KOH)= Normality (meq/mL), of KOH
    WA = sample weight (g)

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