PRODUCT AND PROCESS DEVELOPMENT bromine for three butyl polymers of different unsaturation. Although there is some overlapping for the various polymers, the range of concentration must be raised as the unsaturation of the polymer is increased, in order to obtain optimum properties. The evaluation of the adhesive properties of the polymer a t various bromine levels has shown that the concentration of the haIogen is important in determining the amount of adhesion which is obtained. This is particularly true when the brominated polymer is used as an adhesive between butyl and another elastomer (Figure 15). The bromine required for maximum adhesion must also be adjusted to correspond to the degree of unsaturation. The various ranges for optimum bromine have followed in general the values given in Table VI. Summary and conclusions
Butyl rubber has been modified by attaching bromine to the polymer chain. The reaction has been considered as mainly one of addition to the double bonds, thereby lowering the unsaturation. Both sulfur and metal oxide can serve as vulcanizing agents for brominated butyl, and both may function in the same compound, thus producing a faster rate of cure as compared to butyl. Brominated butyl can also be covulcanized with natural rubber and GR-S, and therefore it is now possible to impart to these rubbers the excellent properties of butyl, such as low air diffusion and resistance to ozone and flex cracking. Still other advantages as compared to butyl rubber are higher modulus and good adhesion to other elastomers and metals. Data have been presented to show that the properties of these new butyl-type polymers can be varied by the amount of bromine which they contain. It has also been shown that there is an optimum range of the halogen concentration required for obtaining the best properties both in mixtures with natural rubber and in brominated butyl polymers used as adhesives. This optimum range of bromine also depends on the original unsaturation of the polymer.
Acknowledgment
The writer wishes to acknowledge the helpful suggestions made by A. E. Juve, W. L. Semon, and D. M. Beach in the preparation of the manuscript. Literature cited (1) Baldwin, F. P., Turner, L. B., and Zapp, R. L., IND.ENO.CHEM.. 36,791-5 (1944). ( 2 ) Borron, H., “Modern Synthetic Rubber,” 2nd ed., pp. 262-3, Chapman & Hall, London, 1943. (3) Buchan, S., “Rubber to Metal Bonding,” pp. 90-1, Crosby Lockwood and Son, London, 1948. (4) Catton, N. L., E. I. du Pont de Nemours & Co., Wilmington, Del., “The Neoprenes,” p. 5, 1953. (5) Chevassus, F., Rev. Gen. Caoutchouc, 23, 168-71 (1946). (6) Craig, D.,Juve, A. E., Davidson, W. L., Semon, W. L., and Hay, D. C . , J . Polymer Sci., 8, 321 (1952). (7) Crawford, R. A., and Morrissey, R. T., U. S.Patent 2,631,984
(1952). (8) Ibid.. 2.681.899 (1954).
