Procedure—
Transfer a quantity of Poloxalene, determined by dividing 420 by the expected hydroxyl value and accurately weighed, to a glass-stoppered, 250-mL conical flask, and add 25.0 mL of
Esterification reagent. Transfer 25.0 mL of
Esterification reagent to a second glass-stoppered, 250-mL conical flask to provide the reagent blank. Add glass beads to the flasks, swirl to dissolve the Poloxalene, and fit both flasks with glass-jointed reflux condensers previously rinsed with 10 mL of pyridine, and heat on a steam bath for 15 minutes. Add 10 mL of pyridine through each condenser, insert the stoppers, and cool under running water for 1 minute. After removing the condensers, add 10 mL of water and 1 mL of
phenolphthalein TS, and titrate with 0.5 N sodium hydroxide VS to a light pink endpoint that persists for at least 15 seconds. Calculate the hydroxyl value by the formula:
(56.11N / W)(B – U),
in which
N is the normality of the 0.5 N sodium hydroxide titrant;
W is the weight, in g, of the Poloxalene taken;
B and
U are the volumes, in mL, of 0.5 N sodium hydroxide consumed by the reagent blank and the solution of Poloxalene, respectively.
[NOTE—If
B minus
U is greater than 10 mL, repeat the test using a smaller sample.
] The hydroxyl value is between 36.0 and 40.0.
;)
791
:
between 5.0 and 7.5, in a solution (1 in 40).
in the solution within 3 mm of the stirring bar. Continue stirring at a rate that minimizes the formation of bubbles. Adjust the hot plate so that the temperature of the solution increases at a rate of about 1