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Home , Decalin

of Polybutadiene with a Soluble Lithium- Cobalt Catalyst

Submitted by: J. C. Falk and J. Van Fleet1 Checked by: M. Morton and E. R. Terrill2

1. Procedure (Note 1) a. Catalyst Preparation

A 0.095 M solution of lithium-cobalt catalyst (molarity based on the amount of cobalt) is prepared in the following way: A solution of 0.0861 mole of n-butyllithium (Note 2) in 287 mL of is placed in a dry, capped pint beverage bottle that has been dried overnight at about 120o and cooled under nitrogen, A solution of 14.1 g of cobalt(II) 2-ethylhexanoate (12% cobalt, w/w) is added with a hypodermic syringe to the cyclohexane solution of n-butyllithium over a period of 90 min. The lithium/cobalt ratio is 3:1. The catalyst is used immediately. b. Polybutadiene Hydrogenation

o Poly-1,4-, 10,000 molecular weight, çsp/c = 0.25 in at 25 , 3.0 g, is dissolved in 150 mL of cyclohexane and placed in a 500 mL Paar reactor bottle (Notes 3 and 4). The system is purged for 10 min with N2 (Matheson prepurified grade) introduced through a long hypodermic needle. The bottle is placed in a Paar reactor and the system is flushed with hydrogen. The n- butyllithium/cobalt(ii) 2-ethylhexanoate catalyst is added with a hypodermic syringe in an amount equal to 0.3 mole% based on butadiene units: 1.17 mL of 0.095 M catalyst. The hydrogen pressure is adjusted to 50 psi and maintained at this pressure throughout the reaction. The reaction mixture is shaken at 50o for 1 h. The polymer- mixture is washed with dilute aqueous acid (1% HNO3), followed by water to remove catalyst residues. The polymer-solvent mixture is coagulated in methanol (1 volume of polymer-solvent mixture to 4 volumes of methanol) o and dried at 50 in a vacuum oven (ca 3 torr) overnight. The yield is 2.9 g (97% recovery); çsp/c = 0.33 dL/g (0.1 g/dL) in decalin at 25o. The IR spectrum of the product shows no cis-, trans-, or vinyl polybutadiene absorptions.

1 2 Macromolecular Syntheses, Collective Volume 2 2. Notes

1. n-Butyllithium is available from the Foote Chemical Co. Cobalt(ii) 2-ethylhexanoate in cyclohexane is available from the Harshaw Chemical Co. and is passed through molecular sieves prior to use. are passed through molecular sieves. All reactions, reagents, and reagent transfers are carried out under a dry nitrogen atmosphere. Polybutadiene is made by anionic polymerization in cyclohexane.3 2. n-Butyllithium must be stored at < 0o or it may lose its activity. 3. Discussed by R. Adams.4 4. The Paar reactor bottle is cleaned carefully prior to use by heating it overnight at 120o and then rinsing it for 15 min with a solution of 5 mL of approximately 1.4 M n-butyllithium in 150 mL of cyclohexane.

3. References

1. R. C. Ingersoll Research Center, Borg-Warner Corporation, Des Plaines, IL. 2. Institute of Polymer Science, University of Akron, Akron, OH 44325. 3. Hsieh, H. L. J. Polym. Sci., 1965, A3, 153. 4. Adams, R. Org. Synth., 1928, 8, 10.