Resin Acid Soaps in G erizatiora JULIAN L. AZORLOSA Hercules Powder Company, Vilmington 99, Del.
Complete polymerization rate curves have been obtained a t 50" C. for a GR-S type system employing as ernulsifier the sodium soap of each of the pure resin acids isolable from natural rosin. From the results presented i t is evident t h a t the resin acid soaps having a conjugated diolefinic structure retarded or inhibited polymerization. Resin acid soaps without aliphatic unsaturation showed the greatest activity in emulsion polymerization, whereas those having nonconjugated unsaturation were somewhat Iess effective. With sodium tetrahydroabietate, a linear relation was found to exist between the eniulsifier concen-
tration and the average polymerization rate within the range of 1 to 10 parts of soap per 100 parts of monomers. Relow 3 critical concentration of about 1 part of soap, the rate fell off rapidly. Employing this same soap, the rate was found to be independent of the catalyst concentration within the range of 0.06 to 0.6 part of pers d f a t e per 100 parts of monomers. Using sodium dehydroabietate as a n emulsifier, polymerization rates were determined a t .EO", 50°, and 59.9" C. The ratios of these rates corresponded to an over-all activation energy for the reaction of 14,500 calories per mole.
i\ soaps have assumed a n important role in emulsion R O Spoll 1 merization, particularly in the production of synthetic elastomeis. The most important example is the use of Dresinate 731 (a disproportionated rosin soap) in the preparation of generalpurpose rubbers of the GR-S type (GR-S-10, GR-S-lOAC, GR-S-1G, GR-S-17, and GR-S-18). In addition, soaps of unmodified rosins as well as Drcsinate 731 are used in the preparation of Types 111, IV, and V GR-Slatices. Rosin soaps are used also in the manufacture of neoprene and are being tested experimentally in a wide vai iety of polymerizations. The rosin emulsifiers generally give polymers with rsceptional tack properties which lead to improved procrs5ing behavior and greater uniformity ( 1 , W, 12). I n view of expanding applications tor various 1 obin soaps, it was important to investigate furthrr the effect of the various components of rosin in emulsion polymerization. It has been established that unmodified rosin is a poor emulsifier for u4e in the GR-S polymerization because certain resin acids and srnall amounts of phenolic rnaterials present act as inhibitors or I etarders in the polymerization (6). The undeairable resin acid components can be converted to desirable forms by disproportionation %ith a hydrogen exchange catalyst (6, 1 1 ) , and the phenolic materials can be removed largely by refining processes (6). Recently several of the resin acids present in gum and wood rosin have been isolated, characterized, and made available for. this experimental worlr by G. C. Harris of this laboratory ( 5 ) . With the exception of Ievopimaric acid, which is not present in mood rosin, and tetrahydroabietic acid, which is not present in gum oleoresin, all of the resin acids shown structurally in Figure 1 are present in both wood rosin and gum oleoresin (4). Some of these pure acids have previously been evaluated as emulsifiers in GR-S polymerization (6). However, a complete polymeriza, tion rate curve was obtained only in the case of dehydroabietic acid. Making use of an efficient method developed a t The B. F. Goodrich Company laboratories for following such reactions ( 7 ) , the present work was undertaken to measure for the first time the polymerization rate curves obtainable with a typical GR-S system using as emulsifiers the sodium soap of each' pure resin acid; and, if possible, to correlate their chemical structure with their behavior in this system. At the same time, some of the variables involved in this type of reaction were studied, employing the pure sodium soaps of dchydroabietic and tetralhydroabietic acids.
EXPEHIMEYTAL
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l t c c r r ~ . Cnless other\\-ise stated, the following recipe was used in this work: Ingredient Sodiuiu soap of t h e pure resin acid (dry basis) Styrene, Dow N99, washed p i t h 10% sodium hydroxide until free of inhibitor. then with distilled water: finallv dried over Drierite and filtered Butadiene, Phillips Petroleum Co., pure grade, 99f mole % Potassium persulfate Baker's C.P. Primary mercaptan (Office of Rubber Reserve Standard DDJZ: a mixture of inercaptans containing approximately 6% Cio, 58% Clr, 26% Cia, with 12% impurities) Distilled water, rediitilled from a dilute hasic permanganate solution
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hismaterial mixed with an effective soap, sodiuni dehydroabietate. Complete GR-S polymerization rate curves were obtained at' 50" C. using 1, 3, and 5% sodium abietate admixed wit,h t,he dehydroabictate soap, as shown in Figure 3. Increasing the amount of abiet,at,e soap decreased the initial rate of the polymerization without changing the slope of the main portion of the curve appreciably, an effect associated with inhibitory act'ion. The relation between the percentage of sodium abiet,ate present and the percentage of mononiers polymerized after 14 hours a t 50" C. is shown in Figure 4. As might be espect,ed,even small aniount,s of abiet,ic acid exerted a marked lowering effect on the activity of dehydroabietic acid. Further rate studies were carried out to determine the effect of varying the temperature, soap concentration, and catalyst concentration in a GR-Sformvla based on a pure resin acid soap. Where possible, the results were compared with those obtained with a fatty acid soap. For this work two pure resin acids, tet'rahydroabiet,ic and dehydroabietic acids, were used because they present t,he least possibility of complicating oxidative side reactions. EFFECT OF EMULSlFIER CONCENTRATION, PERSL LFATE CONCENTRATION, AND TEMPERATURE
Figure 3.
GR-S Polymerization Rates at 50" C.
{;zing various sodium tetrahydroabietate concentrations (parts of soap per 100 parts of monomers. 180 parts water)
resulted, as shown in Figure 5. The rates gradually decreased with decreasing soap concentration, as has been found in the case of fatty acid soap emulsifiers (5). If the emulsifier concentration (parts per 100 parts monomers and 180 parts waterj is plotted against' the average polymerization rate (percentage of monomers polymerized per hour, up to 60% conversion), an interesting relation is obtained, as illustrated in Figure 6. Inspection of this curve reveals a linear relation between the emulsifier concentrat,ion and the average rate in the range of I t o 10 parts of soap. A similar relation has been reported t o exist in the case of sodium oleate-emulsified styrene polymerization (15). Below 1 part of sodiuIii tetrahydroabietate, the rate fell off rapidly to 0.3% mononiers polymerized per hour Jvith no emulsifier. Thc critical soap concentration, about 1 part per 180 parts of water or 1.7 X lop2 molal, is probably re!ated to the limiting concentration necessary for micelle formation. For the purpose of comparison, the critical concentration for a similar soap, pot'assium dehydroabietat,e, can be cit,ed. This was found to be 2.5 to 3.2 X molal at 25.8" C. by a speciral method employing a pinacyano! chloride solut'ion ( 3 ) . I n the case of fatty acid soaps, this critical concentration is apparently much lower ( 9 ) . Similar experiments were conducted a t 50" C. using the standard amount of sodium tetrahydroabietate but varying the catalyst concentration. Within the range 0.06 to 0.6 part of potassium persulfate per 100 parts of monomers, the polymerization rate was found to be independent of the catalyst concentration. Similar observat'ions have been made with fatty acid soaps ( I O ) . To measure the effect of temperature on the GR-Spolymerization rate using pure sodium dehydroabietate, complete rat,c
Several polymerization rate studies were made using the GK-S recipe given in the experimental section, but varying the amount of sodium tetrahydroabietate emulsifiik. B family of curve3
Figure 7. Figure 6. Relation between Sodiwm Tetrahydroabietate >Concentration and GR-S Polymerization Rate at 50" C.
Effect of Temperature on GR-S Polymerization Rate
Using sodium dehydroabietate as emuleifier
August 1949
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
curves were obtained at 4oo, so", and 59.5" C., as shown in Figure 7. Examination of these three curves reveals that, the ratio of the abscissas at any given ordinate is remarkably constant. I n the range of 30 t o 90% conversion, the ratios were 3.89 * 0.05 to 2.06 * 0.02 to 1 at 59.5" C., 50" C., and 40" C., respectively. These temperature coefficients correspond to an over-all activation energy of 14,500 calories per mole. ACKNO W LEDGMEKT
The author expresses thanks to George C. Harris for furnishing the pure resin acids used in this work; to Victoria Gage for aid in carrying out the experimental part of this work; and to John T. Hays and George E. Hulse for suggestions and criticisms helpful in thc preparation of this paper. LITERATURE CITED
(1) Amberg, L. O., IND. ENG.CHEM.,40,487 (1948). ( 2 ) Coe, W.S.,Brady, J. L., and Cuthbertson, G. R., Ibid ,38,975-6 (1946). (3) Corrin, M. L., Klevens, H. B., and Harkins, Wm. D., J . Chem, P h y s . , 14, 480 (1946).
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(4) Harris, G. C., Wood Resins in "Wood Components," TliPPI Monograph No. 6, pp. 167-77, New York, Tech. As~oc. Pulp and Paper Ind., 1948. (5) Harris, G. C., and Sanderson, T., J . Am. Chem. Soc., 70, 334, 339, 2079, 2081 (1948). (6) Hays, J. T., Drake, A . E., and Pratt, Y . T., IND.ENG.CHEM., 39, 1129 (1947). (7) Houston, B. J. (to €5. F'. Goodrich Co.), private cnmtnunicatioii (Jan. 11, 1945). (8) Kluchesky, E. F. (to Firestone Tire and Rubber Co.), private communication (June 15, 1945). (9) communica~, Kolthoff. I. M.. et al. (Univ. of Minnesota), , orivate tion (May 25, 1944). (10) Kolthoff, I. M.. and Harris, W. E., J . Polwmer Sci., 2, 41 (194i). (11) Littmann, E. R. (to Hercules Powder Co.), U. S. 2,154,629 (1939). (12) Starkweather, H. W., et al., IRD.ENG.CHEM.,39, 210 (1947). (13) Vinograd, J. R., and Sawyer, W. M., presented before the Division of Colloid Chemistry at the 108th Meeting of the AMERICAN
CHEMICAL SOCIETY, New York, N. Y.
RBCEIVED January 6 , 1949. Presented as a part of the High Polymer Forum before the Division of Cellulose Chemistry a t the 112th Meeting of t h e AMERICAN CHEMICAL SOCIETS,New York, S . Y.
Dilatometric Measurement of Molecular Regularity in Polymers V. E. LUCAS, P. H. JOHNSON, L. B. WAKEFIELD, AND B. L. JOHNSON The Firestone Tire & Rubber Company, Akron, Ohio T h e molecular regularity of various synthetic elastomers has been determined by measurement of the cry stallizability of the raw, unstretched polymers. The relative crystallizability of the polymers was measured dilatometrically in terms of the isothermal volume decrease characteristic of the ordering process of crystallization. The molecular regularity of polybutadiene polymerized in two different activated emulsion systems has been shown to be dependent on the polymerization temperature; the crystallizability of the polybutadiene in-
creases markedly with decreasing polymerization temperature. A similar relation between polymerization temperature and molecular regularity has been found for a series of polychloroprenes polymerized in an emulsion system employing sodium rainate, sulfur, and ammonium persulfate. The stress-strain properties of gum compound vulcaniistes of the polychloroprenes showed a striking improvement which coincided with increasing crystallizability of the polymers prepared at successively lower polymerization temperatures.
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method, to measure the amount of crystalline material in natural rubber. However, there is still some discrepancy as to the amount of rubber in the crystalline state under various conditions. These techniques have not yet been applied to synthetic polymers and their application may be difficult because of the less intense and less complete x-ray diffraction patterns obtained for many of these polymers. The measurement of volume change upon crystallization has been used successfully to compare relative amounts of crystallization in natural rubber under various conditions ( 1 , $1). .However, this method cannot be used to determine absolute amounts of crystallinity until a more definite value for the density of the crystallites has been established (6, 16). In the case of synthetic polymers, it was thought that determination of volume change might be of value as a measure of the relative degree of regularity resulting under differing conditions of polymerization. The method might be expected to be more sensitive to small differences in regularity of polymers than are x-ray techniques because volume change would be a measure of the total orientation in a polymer chain, even that portion of the 'chain which is not regular enough for x-ray diffractioni.e., imperfect crystallites.
ECEST improvements in the properties of the synthetic rubbers of the GR-S type, have increased the interest in the structure of these polymers; it was felt that the better properties "ere a result of greater molecular regularity of the polymers. An x-ray technique had been developed and appljed by Hanson and Halverson (8) to reveal a limited degree of molecular order in an elongated polybutadiene sample. More recently, Beu and his associates ( 3 )have used the x-ray method to show that the crystallizability of polybutadiene and butadienestyrene copolymers is greatly increased by a decrease in polymerization temperature. It is therefore desirable to investigate all methods which might be of value in measuring the relative degree of crystallizability of these polymers produced under diffei ing conditions of polymerization. A knowledge of the degree of crystallinity present in a polymer is also important on two other considerations. The crystalline regions have been considered to act as centers of reinforcement in gum stocks of crystallizable ,polymers. A more quantitative measure of their effect on tensile strength would, therefore, be desirable. On the debit side of the ledger, the polymers that crystallize readily become stiff in low temperature usage and the crystalline phase should be avoided. X-ray techniques have been used (4, 7 , 80) as an absolute
