1288
Vol. 38, No. 13
INDUSTRIAL A N D ENGINEERING CHEMISTRY
General Formula: G R - S I O O , S Z , Z n O [ B a r d o l 5, E P C B l a c k 4 0
1600t
P AIIQx I +
P b O 1.5
200-
S o n l o c u r e 1.2 A - 5 5 2 0.5 M E T 1.5 DOTG 0.2 Cuprax 1.5
sulfur and zinc soap under vulcanizing conditions. The reaction is promoted by M.B.T. On the basis of the mechanism assumed, the mineral sulfide formed is sufficient to indicate extensive conversion of the olefin to a substituted diallyl disulfide. 4. Assuming the validity of the proposed mechanism, mincral sulfide production indicates substantial disulfide cross linking between a-carbon atoms in conventional cures with natural rubber, and appreciable, though relatively less, cross bonding of this type in the case of GR-S. The smaller extent of this type of cross linking with GR-S is believed to result from greater tendency on the part of this elastomer to add the intermediate mercapto compound to double bonds, as proposed in the first paper of this series.
+
800-
400t
/
ACKNOWLEDGMENT
The writers are pleased to acknowledge the suggestions of 0. IT. Cole of the Firestone Tire & Rubber Company and C. E. Boord of The Ohio State University. They also wish to thank Mary Stingone and Florence Hall for helping with the analytical work. This is a contribution from The Ohio State University Research Foundation, Firestone Tire I%Rubber Company project. LITERATURE CITED
.I 0 .20 .30 S Z ~ SPer - C e n t on G R - S Figure 10. Relation of Zinc Sulfide to Modulus in GR-S Tread Stocks The relatively small tendency of GR-S vulcanizates to form zinc sulfide, and the known tendency of GR-S to stiffen due t o causes unrelated to zinc sulfide formation, make the relation between zinc sulfide and modulus of somewhat questionable significance. However, there is a general trend of increasing modulus with increasing zinc sulfide in these stocks (Figure 10). Attempts to enhance zinc sulfide in GR-S vulcanizates by using soluble zinc and solubilizing agencies in a variety of forms, and by employing various active accelerating combinations, met with little success. It is believed, therefore, that GR-S vulcanization has a decided preference for the mercapto addition reaction ( I I ) , and that a greater percentage of intermolecular additions occur than in the case of natural rubber. Thus, in metal-activated cures, natural rubber vulcanizates may be cross linked principally through disulfide bonds with an occasional thioether cross link, whereas GR-S vulcanizates may be linked chiefly by thioether bonds with a n occasional disulfide link. CONCLUSIONS
The present studies of mineral sulfide in vulcanizate and ‘similar systems support the mercapto-mercaptide-disulfide course of reaction. The results leave little doubt that mercaptides formed during vulcanization would subsequently undergo oxidation by sulfur in preference t o thermal decomposition. Presumably the mercaptide reaction proceeds simultaneously with the addition of sulfhydryl groups to double bonds ( I I ) , so that the nature of the vulcanizate depends upon the relative dominance of these competing reactions. SUMMARY
1. The mechanism proposed by Armstrong, Little, and Doak to explain sulfur vulcanization in the presence of metal soap was investigated in polyprene and simpler systems from the viewpoint of the mineral sulfide produced and, in the case of polyprenes, of the accompanying modulus. 2. Dodecyl mercaptan was found to react with sulfur and zinc soap to produce mineral sulfide equivalent to the oxidation of 80 t o 1 0 0 ~ of o the mercaptan to disulfide; with excess mercaptan substantially quantitative conversion of sulfur or of zinc soap to mineral sulfide can be obtained. 3. Several simple olefins were found to react readily with
(1) Armstrong, R. T . , Little, J. R., and Doak, K. W., IND. ENG, CHEW,36, 628-33 (1944); Rubber Chem. Tech., 17, 788-801. (1944). (2) Bedford, C. W., and Sebrell, L. B., IXD.EXG.CHEM.,14, 25-31, (1922). (3) Brazier, S. A., and Ridgway, L. R , J . S O C Chem. . Ind., 47, T35l6 (1928). (4) Brown, J. R., and Hauser, E. A , IXD,ENG.CHEM.,30, 1291-6 (1938): Rubber Chem. Tech., 12, 43-55 (1939). (5) Farmer, E. H., Trans. Faraday SOC.,38, 340-61 (1942); Rubber Chem. Tech., 15, 765-73 (1942). (6) Guppy, W. D., Trans. Inst. Rubber. Ind., 7, 81-4 (1931); Rubber Chem. Tech., 5, 360-2 (1932). (7) Hauser, E. A., and Brown, J. R., IND.EXG.CHEM.,31, 1225-8 (1939); Rubber Chem. Tech., 13, G5-73 (1940). (8) Luke, L., IND.EXG. C H m f . , ANAL.ED., 15, 602-4 (1943); Rubber Chem. Tech., 17, 227-33 (1944). (9) Martin, G., and Davey, W. S., J . SOC.Chem. Ind., 45, T174-6 (1926). (10) Oldham, E. W., Baker, L. &I., and Craytor, M. W., IXD.ENG. CHEM.,ANAL.ED., 8, 41-2 (1936); Rubber Chem. Tech., 9, 514-19 (1936). (11) Olsen, S. R., Hull, C. M., and France, W. G., IXD.ENG.CHEM., 38, 1273 (1946). (12) Russell, W. F., IND.EM. CHEM.,21, 727-9 (1929). (13) Ibid., U. S . Patent 1,467,197 (1923). (14) Stevens, H. P., Analyst, 40, 275-81 (1915). (15) Ibid., J . SOC.Chem. I d . , 34, 524-6 (1915). (16) Whitby, G. S., and Evans, B. A., Ibid., 47, T122-6 (1928).
c.
PRESENTED before the Division of Rubber Chemistry at the 109th Meetins of the AMERICAN CHEMICAL SOCIETY, Atlantic City, N . J.
Effect of Polymolecularity on Deformation of Butyl PolymersCorrection I n the September issue, this article contains three slight errors which should be corrected as follows: On page 952, second column, immediately after the subheading “Deformation and Flow of Narrow Fractions”, the sentence should road Figure 7 instead of Figure 5. On page 953, first column, second paragraph, fifth line, Figure 6 in the text should read Figure 10. On page 954, second column, the second equation should have a negative slopa and should thus read:
+
log (flow rate) = -5.83 X 10--3m 2.16 v
R. L. ZAPP AND F. P. BALDWIE; Esso LABORATORIES STANDARD OILDEVELOPMENT COMPANY ELIZABETH, 3. J.
