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» Polyisobutylene is a synthetic polymer produced by the low-temperature polymerization of isobutylene in liquid ethylene, methylene chloride, or hexane, using an aluminum-chloride or boron-trifluoride catalyst. It may contain a suitable stabilizer.
Packaging and storage— Preserve in well-closed containers. No storage requirements specified.
Labeling— Label it to indicate the range for intrinsic viscosity or the range for the Staudinger Index, and the name and quantity of any added stabilizer. [note—The Staudinger Index is equal to 100 times the intrinsic viscosity.]
Identification, Infrared Absorption 197F Prepare the sample by dissolving it in hot toluene and evaporating on a salt plate.
Loss on drying 731 Dry a 5-g sample for 2 hours at 105: it loses not more than 0.3% of its weight.
Lead 251 Accurately weigh about 3.3 g of Polyisobutylene, transfer to a porcelain dish, and heat on a hot plate until completely charred. Then heat in a muffle furnace at 480 for 8 hours, and cool. Cautiously add 5 mL of nitric acid, evaporate to dryness on a hot plate, then heat again in the muffle furnace for exactly 15 minutes, and cool. Extract the ash with two 10-mL portions of water, filtering each extract into a separator. Leach any insoluble material on the filter with 6 mL of Ammonium Citrate Solution, 2 mL of Hydroxylamine Hydrochloride Solution, and 5 mL of water, adding the filtered washings to the separator. Continue as directed for Procedure, beginning with “Add two drops of phenol red TS”, and use 10 mL of Diluted Standard Lead Solution (10 µg of lead) for the control: the color of the sample solution does not exceed that in the control (0.0003%).
Viscosity 911
Solvent— Use isooctane.
Test solution— Prepare a solution of Polyisobutylene in the Solvent having a known concentration as indicated in Table 1. [notes—The solution must be homogeneous before testing. For the Polyisobutylene having a Staudinger Index of 100 and higher, add the Solvent to the weighed material, and allow it to stand in an oven at 80 for 12 to 24 hours. A heated mechanical shaker may be used to shorten the dissolution time; it is recommended that a gentle shaker be used to avoid shearing the polymers. Take adequate precautions to prevent evaporation of the solvent.]
Table 1
Staudinger Index1 Concentration, g per cm3
25–60 0.01
60–100 0.005
100–350 0.002
350–700 0.001
1  The Staudinger Index is equal to 100 times the intrinsic viscosity.
Procedure— Using a suitable Ubbelohde capillary viscosimeter having dimensions such that the flow time is not less than 200 seconds, immersed in a controlled temperature bath, measure the flow of the Solvent and of the Test solution at 20. Repeat the procedure three times, and calculate the average. [note—Before each measurement, let the solutions be temperature equilibrated for 10 minutes.]
Calculate the reduced viscosity, J, by the formula:
(t / t0 – 1) / C
in which t0 is the average flow time, in seconds, of the Solvent; t is the average flow time, in seconds, of the Test solution; and C is the concentration, in g per cm3, of the Test solution.
Calculate the Staudinger Index, J0, by the formula:
J / [1 + 0.31 (t / t0 – 1)]
in which the terms are defined above: it is within the limits specified on the label.
Auxiliary Information— Please check for your question in the FAQs before contacting USP.
Topic/Question Contact Expert Committee
Monograph Hong Wang, Ph.D.
(EM205) Excipient Monographs 2
Reference Standards Lili Wang, Technical Services Scientist
USP32–NF27 Page 1313
Pharmacopeial Forum: Volume No. 32(3) Page 828