February I948
INDUSTRIAL AND ENGINEERING CHEMISTRY
paints would be expected t o give the best service. This can be determined only by exposures of the paints in the sea and their performance on ships in service. LITERATURE CITED
v.,
(1) Borsook, H.,and Thimann, K. J . B i d . C h e w 98, 671-745 (1932). (2) Callan, T., and Henderson, J. A. R., AnuZUst, 54, 850-3 (1929). (3) Coulsoa, E. J., J. -48Wc. ofic&d Agr. Chm., 19, 219-28 (1936); 20, 178-88 (1937). (4) Ferry, J. D., and Carritt, D. E., IND. ENG.CHEM.,38,612 (1946).
253
(5) Ferry, J. D., and Ketchum, B. H., Zbid., 38,806(1946). (6) Ferry, J. D.1 and Riley, G. A., Ibid., 38,699 (1946). (7) Ketchum, B. H., Ferry, J. D., and Burns, A. E., Jr., Zbid., 38, 931 (1946). --, (8) Ketchum, B. H., Ferry, J. D., Redfield, A. C., and Burns, A. E. Jr., Zbid., 37,456 (1945).
.--
RECBIVED December 11,1946.
Contribution 398 of the Woods Hole Oceanographic Institution. These experiments were conducted under contract with the Bureau of Ships, U. S. Navy Department, which has given permiseion for their publication. The opiniona preaented here are those of the author and do not necessarily reflect the official opinion of the Navy Department or the naval service a t large.
Physical Properties of Diene Polymers J
EFFECTS OF SIDE VINYL GROUPS AND OTHER STRUCTURAL FEATURES JAMES D. D’IANNI, Research Laboratory, Goodyear Tire & Rubber Company,Akron, Ohio Natural rubber, emulsion polyisoprene, polyisoprene prepared with a special organometallic catalyst, and sodium polyisopreneshowed decreasing amounts of 1 4 -addition content in the order listed, by comparison of data available from infrared absorption spectra, perbenzoic acid titration, refractive index, density, iodine number, chromic acid oxidation, and hydrochlorination. Similar data indicated decreasing 1,4- addition content for emulsion polybutadiene, polybutadiene prepared with a special organometallic catalyst, and potassium polybutadiene (Buna 85) in the order listed, as well as for the copolymers GR-S and butadiene-styrene 75/25 copolymers prepared with a special organometallic catalyst and with sodium. Correlation of structure inferred from the above data with physical properties o f corresponding tread stock d c a n i zates indicated, for the diene polymers of approximately the same molecular weight range made with the same monomer, that with decreasing amount of 1,4- addition content the brittle point rose, the rebound value decreased, and the tensile strength increased. Natural rubber was unique because it was substantially a linear high polymer with the cis- configuration around all the double bonds. For the butadiene-styrene copolymers the brittle point rose with decreasing amount of 1,4- addition content, but no satisfactory correlation could be obtained for the tensile strength and the rebound value, probably because of the predominant effect of the phenyl side groups.
M
UCH information about the detailed molecular structure of rubberlike polymers has been accumulated during the past few yearb. In this paper an attempt ismade to evaluate the available information particularly concerning the relative amounts of of 1,4, 1,2-, and 3 , 4 addition content of isoprene and butadiene polymers and copolymers prepared by different methods of polymerization, as determined from infrared absorption spectra, perbenzoic acid oxidation, specific refraction, and iodine number. Further useful information was collected for natural rubber and other isoprene polymers on the basis of common chemical reactivity (6). Data on the molecular structure of a number of rubberlike polymers were recently summariaed by Flory (7,8). The second purpose of the paper is to correlate the structural features of the various polymers, aa deduced from the data indicated above, with certain properties of the corresponding tread
stock vulcanizates, such as tensile strength, rebound vahe, and brittle point. No results were reported on the ozonolysis of synthetic polymers, since recent reports (18, 21) shpwed that even natural rubber gave a “blank” value corresponding to 10 to 17% side vinyl groups, depending upon the procedure employed. STRUCTURES AND PROPERTIES OF ISOPRENE POLYMERS
Several physical and chemical methods were available, by means of which much information about the detailed molecular structures of rubberlike polymers could be obtained. The study of isoprene polymers was of particular value because of the naturally available controls, rubber and gutta percha, and the much greater chemical reactivity towards certain reagents shown by isoprene polymers than by butadiene polymers. Isoprene can enter the polymer in all the following ways:
CHs -CH~-C=CH-CH~-
bHa 1,4- addition
-CH2-C-
I I
CH CH,.
I,% addition
-CH2-CH-
I
C-CHI jlH2 3,4- addition
Upon the basis of x-ray (9), ozonolysis (IO,l 7 ) , and infrared data (6, $2, $3, 25) natural rubber is now generally considered to be a polyisoprene made up of isoprene units attached exclusively by 1,4addition in a head-to-tail fashion and with the groups attached to the olefinic linkages in the cis- configuration; gutta percha differs primarily in that the groups are attached in the trans- configuration. There is no absolute proof, however, that the above structure is a quantitative picture of the rubber molecule, for the possibility still exists of the presence of some side vinyl groups, some of the groups attached to the olefinic linkage in the trans- configuration, and some branching and cyclic structures. Furthermore, there is no proof that rubber is formed in the tree by polymerization of isoprene; it is as likely that a condensation process is involved. The perbenzoic acid method (24) of titration for double bonds has been used extensively for differentiation between internal double bonds (1,4-addition) and external double bonds (1,s addition) on the basis that the rate of reaction with the former was much greater than with the latter. A total unsaturation of
INDUSTRIAL AND ENGINEERING CHEMISTRY
254
TABLE I. PROPERTIES OF ISOPRENE POLYMERS Polyisol.irene
Polymer Ptriicturai featores By infrared By perbenzoic acid Refractive indes at 25' Density a t 2 5 O Iodine No.
Watnrai Rubber
Emulsion Polyisoprene
Ail 1,4-? cis- iso- 90% 1.4- (6) iner (6, 9, ici, 17, 22, 23. 25) 98.8'% unsat. All 1,4-? ( 2 4 )
1.519-1.520
0.92 352-357 (95-965.;)
(12)
( 0r g a no -
inctaliic Catalyst)
Sodium Polyisoprene
